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Preview: Die Angewandte Makromolekulare Chemie

Macromolecular Materials and Engineering



Wiley Online Library : Macromolecular Materials and Engineering



Published: 2017-09-01T00:00:00-05:00

 



A Novel NIR Laser Switched Nanocomposite Hydrogel as Remote Stimuli Smart Valve

2017-09-22T01:08:06.975761-05:00

Thermosensitive nanocomposite (NC) hydrogels are considered as a significant kind of intelligent material to be utilized as sensor, biomaterial, drug carrier, etc. Recently, preparation of remotely controlled NC hydrogel with high-performance attracts more and more concern. To produce facile remote-stimuli thermosensitive NC hydrogel, a novel near-infrared (NIR) laser switched CuS/clay/poly(OEGMA-co-MEO2MA) hydrogel is demonstrated, which can be precisely remote-stimulated by NIR irradiation based on the excellent NIR photothermal conversion property of CuS nanoparticle. The temperature change of hydrogel is related to the NIR intensity, CuS content, and crosslinking density. Moreover, the influences on dimensional variation of hydrogel on macroscale are systematically studied, and the hydrogel as smart liquid valve is further utilized which can be remotely controlled by NIR switch on/off successfully. Cyclic test illustrates that this novel CuS/clay/poly(OEGMA-co-MEO2MA) hydrogel exhibits stable cyclic volume transition property which has promising applications in the areas of sensors, valves, and intelligent switches. To produce facile remote-stimuli thermosensitive nanocomposite hydrogel, a novel near-infrared (NIR) laser switched CuS/clay/poly(OEGMA-co-MEO2MA) hydrogel is fabricated. The temperature change and dimensional variation of hydrogel are related to the NIR intensity, CuS content, and crosslinking density. The hydrogel can be utilized as smart liquid valve, which can be remotely controlled by NIR switch on/off successfully.



Epoxy-Based Azopolymers with Enhanced Photoresponsive Properties Obtained by Cationic Homopolymerization

2017-09-22T01:00:29.251378-05:00

Azopolymers are highly versatile materials due to their unique photoresponsive properties. In this contribution, a novel azo-modified epoxy network is synthesized by cationic homopolymerization with boron trifluoride monoethylamine (BF3.MEA) complex as initiator. The effect of the addition of a fixed content of amino-functionalized azo chromophore, Disperse Orange 3, into the polymer matrix is studied in detail. First of all, the thermal curing cycle is optimized by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) measurements. Then, the resulting bulk azo-modified epoxy networks are characterized by means of thermogravimetric analysis (TGA), FTIR, DSC, UV–vis spectroscopy, and rheological measurements. Finally, the optical response of thin films of these materials is determined. The results evidence that azo-modified epoxy networks obtained by cationic polymerization with optimized curing cycle display high Tg values, high maximum photoinduced birefringence, fast writing speed, and exceptionally high remnant anisotropy. Therefore, this material is a promising candidate to be used for optical storage applications. A new type of azo-modified epoxy network has been prepared by the way of cationic homopolymerization with boron trifluoride monoethylamine (BF3·MEA) complex as initiator. The resulting networks are promising materials for optical storage applications.



Amorphous Electrically Actuating Submicron Fiber Waveguides

2017-09-21T01:31:21.802114-05:00

Amorphous electrically actuating submicron fiber waveguides are promising building blocks for creating novel opto-electromechanical devices. In this study, waveguiding and electrically actuating properties of the waveguides composed of racemic poly(lactic acid) and a dye are investigated. The fibers have mean diameters of <0.4 µm, and each fiber demonstrates subwavelength waveguiding with a loss coefficient of 1.5 × 10−4–8.3 × 10−4 µm−1 at 0.63 µm wavelength. Light propagates with a near-light speed group velocity between wavelengths of 0.59 and 0.63 µm, where the fraction of power inside the core is 0.13–0.28. The fiber mat thicknesses change in response to both the polarity and the magnitude of an applied voltage, similar to the inverse-piezoelectric effect. The estimated values for both the apparent piezoelectric constant (29 000 × 10−12 m V−1) and Young's modulus (1.5 kPa) indicate a high degree of electricity actuation and a soft mat. Extremely small, soft, and electrically actuating waveguides can produce novel opto-electromechanical devices. The properties of novel electrically actuating and waveguiding amorphous polymer submicron fibers are investigated in detail. These fibers guide light at subwavelength diameters with a group velocity greater than 0.71c0. The fiber mat also demonstrates electrical actuation with a high apparent piezoelectric constant of ≈29 000 × 10−12 m V−1. Extremely small and functional waveguides can be used to produce novel opto-electromechanical devices.



Ionically Crosslinked Thermoresponsive Chitosan Hydrogels formed In Situ: A Conceptual Basis for Deeper Understanding

2017-09-20T03:17:46.24949-05:00

In situ formation and the performance of ionically crosslinked thermosensitive chitosan-based hydrogels are presented. Experimental analyses, together with mechanistic descriptions of the events during hydrolysis, are employed to uncover the role of urea and isobutanol as chemical modifiers by comparing three classes of hydrogels formed in chitosan/β-glycerolphosphate (β-GP) solutions. Rheological measurements demonstrate that urea caused an increase in gelation time and temperature of chitosan/β-GP systems, while isobutanol has an inverse effect. Interpretations based on increase in pH and chemical bonding of components in chitosan solutions provide further insight into hydrogel network formation. Urea can hinder the hydrophobic characteristics of chitosan-based hydrogels, whereas isobutanol has the opposite effect. The shape retaining strategy applied here helps in simulation and interpretation of performance of thermosensitive hydrogels for biomedical purposes. This study uncovers the role of urea and isobutanol as chemical modifiers by comparing three classes of hydrogels. An increased or a decreased pH affects gelation, where the best conditions for gelation would be achievable in the case of neutral medium. Either a rise or a fall in pH value upsets the balance between electrostatic interactions and crosslinking, the driving forces behind gelation.



Biodegradable Inorganic–Organic POSS–PEG Hybrid Hydrogels as Scaffolds for Tissue Engineering

2017-09-20T03:16:09.516814-05:00

Biodegradable hydrogels have attracted much attention in tissue engineering due to their good biocompatibility and elastomeric behavior. In this work, a series of inorganic–organic polyhedral oligomeric silsequioxanes–poly(ethylene glycol) (POSS–PEG) hybrid hydrogels are prepared by covalently grafting POSS into PEG and further cross-linked by matrix metalloproteinase (MMP) degradable peptide via Michael-type addition polymerization. All the POSS–PEG hybrid hydrogels have a porous structure and high hydrophilic ability, and the grafted hydrophobic POSS macromers result in a higher mechanical properties and lower equilibrium swelling ratio. Additionally, the hydrogels can be biodegraded by MMP-2 solution and the POSS loading level can influence the degradation rate. It is worth mentioning that POSS-containing hybrid hydrogels can be prepared in water and be used for 3D cell culture. In vitro cell viability study on human umbilical vein endothelial cells for 3D cell culture indicates POSS–PEG hydrogels have good compatibility. All of these results suggest that these POSS–PEG hybrid hydrogels exhibit the potential for tissue engineering scaffolds. A series of inorganic–organic polyhedral oligomeric silsequioxanes–poly(ethylene glycol) (POSS–PEG) hybrid hydrogels are prepared in water by covalently grafting POSS into PEG and further cross-linked by matrix metalloproteinase degradable peptide via Michael-type addition. All POSS–PEG hybrid hydrogels have a porous structure, high mechanical properties and hydrophilic ability, good biodegradability and biocompatibility.



Enhanced Piezoelectric Performance of Electrospun Polyvinylidene Fluoride Doped with Inorganic Salts

2017-09-13T13:30:53.02638-05:00

A novel approach to preparing electrospun polyvinylidene fluoride (PVDF) nanofibers is proposed, with high piezoelectric performance. PVDF nanofibers are doped with inorganic salts without the use of any postpolarization treatment. Twenty-six salts are doped into the nanofibers and their piezoelectric properties are studied. The salts are classified into three groups based on their differing piezoelectric enhancement effects. A piezoelectric nanogenerator fabricated with an optimized electrospun PVDF nanofiber mat shows a piezovoltage seven times greater than that of a device based on undoped nanofibers. The simple and low-cost approach to fabricate these piezoelectric nanofiber mats may broaden the range of industrial applications of these materials in energy-harvesting devices and portable sensors. The piezoelectric performance of electrospun polyvinylidene fluoride nanofiber piezoelectric nanogenerators is increased obviously by doping inorganic salts. This simple and low-cost approach may open the way for new applications of miniature energy-harvesting devices.



Surface Modification of Electrospun TPU Nanofiber Scaffold with CNF Particles by Ultrasound-Assisted Technique for Tissue Engineering

2017-09-13T13:29:41.210776-05:00

A straightforward, fast, and versatile technique is developed to fabricate nanofibrous scaffold with excellent hydrophilicity, mechanical properties, and biocompatibility for tissue engineering. The thermoplastic polyurethane (TPU) nanofiber is fabricated by utilizing electrospinning, and then its surface is modified through simply immersing it into cellulose nanofibrils (CNF) dispersion and subjecting to ultrasonication. The results show that the CNF particles are successfully absorbed on the surface of TPU nanofiber. By introducing CNF particles on the surface of TPU nanofiber, the hydrophilicity, mechanical properties of fabricated CNF-absorbed TPU scaffold are significantly increased. Additionally, the adhesion and proliferation of human umbilical vein endothelial cells cultured on CNF-absorbed TPU scaffold are prominently enhanced in comparison with those of cultured on TPU scaffold. These findings suggest that the ultrasound-assisted technique opens up a new way to simply and effectively modify the surface of various scaffolds and the modified scaffold could be shown a great potential in tissue engineering. A novel method is developed to modify the surface of thermoplastic polyurethane (TPU) nanofiber with cellulose nanofibril (CNF) particles. CNF particles are successfully used as a modifier to improve the hydrophilicity, water retention ratio, mechanical property and biocompatibility of TPU scaffold. These finding suggest that the ultrasound-assisted technique opens up a new way to simply modify the scaffold surface.



Pore Size Distribution and Blend Composition Affect In Vitro Prevascularized Bone Matrix Formation on Poly(Vinyl Alcohol)/Gelatin Sponges

2017-09-12T00:46:52.74263-05:00

This study aims at identifying compositional and architectural (pore size and distribution) parameters of biocompatible scaffolds, which can be best suitable for both osteoblasts and endothelial cells to produce optimized 3D cocultured constructs. Spongy scaffolds are prepared using poly(vinyl alcohol) (PVA) and gelatin (G) at different weight compositions (PVA/G range: 100/0–50/50, w/w) via emulsion and freeze-drying. The higher the gelatin content, the larger is the volume occupied by higher size pores. Human umbilical vein endothelial cells and human mesenchymal stromal cells are independently differentiated on the scaffolds to select the best candidate for the coculture. The results of metabolic activity and histology on single platforms show both cell- and material-type dependent outcomes. PVA/G 80/20 scaffolds are finally selected and allow the formation of mineralized matrix containing organized endothelial-like structures. This study highlights the need for systematic investigations on multifactorial parameters of scaffolds to improve vascularized bone substitutes. Poly(vinyl alcohol) (PVA)/gelatin scaffolds are produced via emulsion and freeze-drying from 100/0 to 50/50 (w/w) compositions. Changing composition affects pore size distribution and biological response of endothelial cells and mesenchymal stromal cells, including metabolic activity and differentiation. PVA/gelatin 80/20 scaffolds allow the formation of mineralized matrix containing organized endothelial-like structures. Systematic investigations on physicochemical and architectural features can improve vascularized bone substitutes.



Highly Luminescent CB[7]-Based Conjugated Polyrotaxanes Embedded into Crystalline Matrices

2017-09-12T00:46:31.138535-05:00

π-Conjugated polymers suffer from low quantum yields (QYs) due to chain–chain interactions. Furthermore, their emission in solid films is significantly quenched due to aggregation leading further decrease in QY. These are the two main issues of these materials hampering their widespread use in optoelectronic devices. To address these issues, here the backbone of poly(9,9′-bis(6″-(N,N,N-trimethylammonium)hexyl)fluorene-alt-co-thiophenelene) is isolated by threading with cucurbit[7]uril (CB7). Subsequently, the conjugated polyrotaxanes are incorporated into organic crystalline matrices to obtain highly efficient color-converting solids suitable for solid-state lighting. Upon threading the polymer backbone with CB7s, although the QY of the resulting polyrotaxane in solution state increases, the quenching problem in their solid state is not completely tackled. To solve this problem, these conjugated polyrotaxanes are embedded into various crystalline matrices and their remarkably high QYs (>50%) in the solution are successfully maintained in the solid state. To demonstrate the suitability of these aforementioned materials for solid-state lighting, a proof-of-concept light-emitting diode is constructed by employing their powders as color converters. Conjugated polyrotaxanes are incorporated into organic crystalline matrices to obtain highly efficient color converting solids suitable for solid-state lighting.



Balancing Block Copolymer Thickness over Template Density in Graphoepitaxy Approach

2017-09-12T00:46:16.588964-05:00

Directed self-assembly (DSA) of block copolymers (BCP) is one of the most promising patterning solutions for sub-10 nm nodes. While significant achievements are demonstrated in pattern fidelity for various applications (contact shrink, line patterning), some challenges are still needed to be overcome especially regarding the defect density reduction, in order to ensure DSA insertion in high-volume manufacturing. In particular, in the case of the graphoepitaxy approach, a remaining challenge is to solve the pattern-densities-related defect issue due to BCP film thickness variation inside the guiding template. In order to address this issue, a new DSA process flow called “DSA planarization” is employed for contact-hole patterning, and consists in overfilling the guiding pattern cavities with a thick BCP film, followed by a plasma etch-back step. This new approach ensures a uniform control of the final thickness of the BCP inside guiding cavities of different densities, as demonstrated herein by AFM measurement. Thus, defect-free isolated and dense patterns for both contact shrink and multiplication are simultaneously resolved. Furthermore, the simulation results of BCP self-assembly overfilling the templates demonstrate that BCP domains are well-directed in vertical cylinders ordering inside guiding cavities, which confirms the experimental results and the viability of this approach. Uniform block copolymer (BCP) thickness over template density is achieved using a new and simple graphoepitaxy process flow called “directed self-assembly (DSA) planarization.” Simulations and SEM characterizations of BCP self-assembly overfilling the guiding patterns confirm the viability of this approach. Experimental results demonstrate the enhancement of DSA performances when using the DSA planarization flow.



Ionic Liquid Approach Toward Manufacture and Full Recycling of All-Cellulose Composites

2017-09-06T11:15:23.803735-05:00

All-cellulose composites (ACCs) are prepared from high-strength rayon fibers and cellulose pulp. The procedure comprises the use of a pulp cellulose solution in the ionic liquid (IL) 1-ethyl-3-methyl imidazolium acetate ([EMIM][OAc]) as a precursor for the matrix component. High-strength rayon fibers/fabrics are embedded in this solution of cellulose in the IL followed by removal of the IL. Different concentrations of cellulose in the IL are investigated and the mechanical properties of the final ACCs are determined via tensile, bending, and impact testing. ACCs prepared in this study show mechanical properties comparable to thermoplastic glass fiber-reinforced plastics. Apart from being bio-based, they possess several advantages such as biodegradability and full recyclability. The recycling of ACCs is successfully demonstrated in several cycles by using the recycled cellulose for subsequent matrix preparation. The manufacture of all-cellulose composites (ACCs) reinforced with high-strength rayon fibers is reported. Solutions of cellulose in the ionic liquid 1-ethyl-3-methyl imidazolium acetate are used as matrix precursors. Full recycling of these ACCs is successfully demonstrated in several cycles by using the recycled material for subsequent matrix preparation without any significant loss in mechanic performance.



Influence of Annealing on Mechanical αc-Relaxation of Isotactic Polypropylene: A Study from the Intermediate Phase Perspective

2017-09-05T12:00:49.478877-05:00

The influence of annealing on mechanical αc-relaxation of isotactic polypropylene (iPP) is investigated. In the sample without annealing, polymer chains in the intermediate phase are constrained by crystallites with a broad size distribution, leading to one αc-relaxation peak with activation energy (Ea) of 53.39 kJ mol−1. With an annealing temperature between 60 and 105 °C imperfect lamellae melting releases a part of the constraining force. Consequently, two αc-relaxation peaks can be observed (αc1- and αc2-relaxation in the order of increasing temperature). Both relaxation peaks shift to higher temperatures as annealing temperature increases. Ea of αc1-relaxation decreases from 38.43 to 35.55 kJ mol−1 as the intermediate phase thickness increases from 2.0 to 2.2 nm. With an annealing temperature higher than 105 °C, a new crystalline phase is formed, which enhances the constraining force on the polymer chains. So the αc1-relaxation peak is broadened and its position shifts to a higher temperature. Moreover, the polymer chains between the initial and the newly formed crystalline phase are strongly confined. Therefore, the αc2-relaxation is undetectable. Ea of αc1-relaxation decreases from 23.58 to 13.68 kJ mol−1 as the intermediate phase thickness increases from 2.3 to 3.0 nm. Mechanical αc-relaxation of isotactic polypropylene can be greatly influenced by the constraint force on polymer chains in the intermediate phase. Imperfect lamellae melting caused by annealing leads to a nonhomogeneous intermediate phase, giving rise to two mechanical αc-relaxation. Lamellae thickening enhance the constraint force on polymer chains in the intermediate phase, resulting in an increase of the mechanical αc-relaxation temperature.



Novel Macromolecular Emulsifiers as Coatings with Water-Tolerant Antifogging Properties Based on Coumarin-Containing Copolymeric Micelles

2017-08-28T05:30:51.05224-05:00

An efficient macromolecular emulsifier as water-tolerant antifogging coating based on coumarin-containing copolymeric micelles is reported. Compared to the previous work using poly(methyl methacrylate-co-2-(dimethylamino)ethyl methacrylate), coumarin unit in copolymer-based coating can be photo-crosslinked under UV light to form an interchain network, successfully avoiding the use of chemical crosslinking agents. Coumarin unit in the amphiphilic copolymer can be photo-crosslinked under UV light irradiation to form an interchain network, effectively avoiding the use of chemical crosslinking agents. A possible antifogging mechanism is that the water molecules are absorbed into the hydrophilic chains of the coatings and droplets are not attached to the surface.



High-Impact Polyamide Composites with Linear Ethylene–Norbornene Anhydride Copolymers from Insertion Polymerization

2017-08-23T12:18:11.558467-05:00

Toughening of polyamide 66 with novel linear norbornene anhydride functionalized polyethylenes leads to an impact performance in the Charpy-notch impact testing at 23 °C and −30 °C as high as aCN = 18.0 ± 1.0 and 13.7 ± 0.8 kJ m−2, respectively, which compares favorably to a state of the art functional low density polyethylene (LDPE) from high-pressure copolymerization with a Charpy-notch impact strength of aCN = 16.8 ± 0.0 and 13.8 ± 2.1 kJ m−2 at 23 and −30 °C, respectively. The linear copolymers are obtained by insertion polymerization at mild ethylene pressures of 5 to 15 bars with phosphinesulfonato Pd (II) catalysts, to yield linear copolymers with norbornene anhydride incorporations as high as 4.8 mol% along with a polymer molecular weight of >105 g mol−1. Furthermore, the norbornene anhydride functionality serves as a reaction site for postpolymerization functionalization with alcohols to obtain the respective half- and diesters of the anhydride functionality. Notably, the impact performance is improved with the increase of the alkyl chain length and degree of branching of the ester functionality in the order methanol < n-butanol < 2-ethyl hexanol from 10.0 to 13.8 kJ m−2. Norbornene-anhydride-functionalized linear polyethylenes from catalytic insertion copolymerization under mild conditions provide a high impact resistance to nylon-6,6 that compares favorably to existing impact modifiers, at ambient and low temperatures. Morphologies of the blends underline a strong binding between the microphases.



3D Printing of BaTiO3/PVDF Composites with Electric In Situ Poling for Pressure Sensor Applications

2017-08-23T12:17:33.664791-05:00

This paper presents 3D printing of piezoelectric sensors using BaTiO3 (BTO) filler in a poly(vinylidene) fluoride (PVDF) matrix through electric in situ poling during the 3D printing process. Several conventional methods require complicated and time-consuming procedures. Recently developed electric poling-assisted additive manufacturing (EPAM) process paves the way for printing of piezoelectric filaments by incorporating polarizing processes that include mechanical stretching, heat press, and electric field poling simultaneously. However, this process is limited to fabrication of a single PVDF layer and quantitative material characterizations such as piezoelectric coefficient and β-phase percentage are not investigated. In this paper, an enhanced EPAM process is proposed that applies a higher electric field during 3D printing. To further increase piezoelectric response, BTO ceramic filler is used in the PVDF matrix. It is found that a 55.91% PVDF β-phase content is nucleated at 15 wt% of BTO. The output current and β-phase content gradually increase as the BTO weight percentage increases. Scanning electron microscopy analysis demonstrates that larger agglomerates are formulated as the increase of BTO filler contents and results in increase of toughness and decrease of tensile strength. The highest fatigue strength is observed at 3 wt% BTO and the fatigue strength gradually decreases as the BTO filler contents increases. The fabrication of piezoelectric pressure sensors with BaTiO3 (BTO) nanoparticles in a poly(vinylidene) fluoride (PVDF) matrix through electric in situ poling during the FDM 3D printing process is presented. The enhanced electric poling-assisted additive manufacturing process enables to polarize dipoles of PVDF and BTO to longitudinal direction.



Surface Modification of Polyhydroxyalkanoates toward Enhancing Cell Compatibility and Antibacterial Activity

2017-08-18T01:56:23.454313-05:00

Biomaterials for in vivo application should induce positive interaction with various histocytes and inhibit bacteria inflection as well. Cells and/or bacteria response to the extracellular environment is therefore the basic principle to design the biomaterials surface in order to induce the specific biomaterial–biological interaction. Polyhydroxyalkanoate (PHAs) are of growing interests because of their natural origin, biodegradability, biocompatibility, and thermoplasticity; however, quite inert and intrinsic hydrophobic characteristics have hindered their extensive usage in medical applications. Surface modification of PHAs tailors the chemistry, wettability, and topography without altering the bulk properties, and introduces specific proteins/peptides and/or antibacterial agents to mediate cell–matrix interactions. This review describes the recent developments on the surface modification of PHAs to construct cell compatible and antibacterial surfaces. Inert and hydrophobic characteristics of polyhydroxyalkanoates (PHAs) have limited in vivo biomedical applications. Surface modifications to introduce reactive functional groups add valuable attributes to PHAs, which can further immobilize specific proteins/peptides and/or antibacterial agents to mediate cell–matrix interactions. This review describes the recent developments on the surface modification of PHAs to tailor the interactions with cells or bacteria in vivo.



Novel Core–Shell PS-co-PBA@SiO2 Nanoparticles Coated on PP Separator as “Thermal Shutdown Switch” for High Safety Lithium-Ion Batteries

2017-08-18T01:51:38.182667-05:00

Thermal runaway is a hazardous behavior of lithium-ion batteries under extreme conditions and is mainly cause for restraint of its commercial applications in development of high-power and high-rate lithium-ion batteries. In this paper, a new dual-functions coating layer fabricated from polystyrene-poly(butyl acrylate) copolymer encapsulated silica nanoparticles as “thermal shutdown switch” with a reasonable shutdown temperature of ≈80 °C is designed and coated on polypropylene separator. The shell polymer owing to its self-adhesion upon glass transition temperature (Tg) can retard off the Li+ conduction between the electrodes, thus prevents cell from thermal runaway, the core nanoparticles protect the separator from significantly thermal shrinkage when the cell temperature keeps going up. Moreover, the coated separator has no negative affection on the normal electrochemical performance of the batteries, thereby implying that this coating layer provides a simple and effective approach to control the safety of commercial lithium-ion batteries by internal self-protecting. Polystyrene-poly(butyl acrylate) copolymer (PS-co-PBA) encapsulating (3-(methacryloxy)propyl) trimethoxysilane-treated SiO2 is prepared by free radical polymerization and coated on polypropylene separator. The coating layer through glass transition can retard off ion transport to protect Li-ion batteries at risk temperature.



Microfluidic Fabrication of Physically Assembled Nanogels and Micrometric Fibers by Using a Hyaluronic Acid Derivative

2017-08-18T01:51:15.863017-05:00

The employ of a hyaluronic acid (HA) derivative, bearing octadecyl (C18) and ethylenediamine (EDA) groups, for microfluidic fabrication of nanogels and microfibers is reported in this study. Two HA-EDA-C18 derivatives (125 and 320 kDa) having ionic strength sensitive properties are synthesized and characterized. The control of the rheological properties of HA-EDA-C18 aqueous dispersions by formation of inclusion complexes with hydroxypropyl-β-cyclodextrins (HPCD) is described. Reversibility of C18/HPCD complexation and physical crosslinking is detected in media with different ionic strength through oscillation frequency tests. HA-EDA-C18 125 kDa is employed for nanogel fabrication. Control over nanogel dimension by flow ratio regulation is demonstrated. HA-EDA-C18 320 kDa with HPCD is employed for fabrication of both microfibers and microchannels. Dimension of fibers is controlled by modulating flow ratios. Suitability for biological functionalization is assayed introducing cell adhesive peptides. Adhesion and encapsulation of human umbilical vein endothelial cells is evaluated. Microfluidic fabrication of biomaterials by using ionic strength sensitive hyaluronic acid derivatives is described. Rheological characterization demonstrates the salt sensitive coacervation of hyaluronic acid derivatives depending of media ionic strength. Hydroxypropyl-β-cyclodextrins are employed to control fluidity of polymer dispersion without affecting crosslinking properties. Biomaterials fabrication is performed by using very mild conditions suitable for a safe cell encapsulation.



Cocoa Shell Waste Biofilaments for 3D Printing Applications

2017-08-17T07:46:59.27212-05:00

In this study, biofilaments based on cocoa shell waste, a by-product of the chocolate industry, and biodegradable poly(ε-caprolactone), PCL, have been prepared using a single-screw extruder. Micronized cocoa shell waste is compounded in the polymer up to 50% by weight without significant alteration of its crystalline structure. Resultant elastic (Young's) modulus of biofilaments remains close to that of pure PCL. Scanning electron microscopy results indicate that micronized cocoa shell waste is homogeneously dispersed in the polymer during the extrusion process. Detailed thermal characterization measurements on the extruded filaments allow tuning of the fused deposition modeling 3D printing parameters. 3D printed items display a well-defined structure with good adhesion between deposition layers and fine resolution. Hence, with this simple and solvent-free fabrication technique, uniformly structured cocoa shell waste biofilaments can be produced in a very reproducible manner and can be used in 3D printing of diverse objects with potential household and biomedical applications. Direct valorization of cocoa shell waste, a by-product of the chocolate industry, for the fabrication of low-cost biofilaments for 3D printing application at lower 3D printing temperatures compared to standard filaments and highly reproducible process is reported.



Oil–Water Separation Using Superhydrophobic PET Membranes Fabricated Via Simple Dip-Coating Of PDMS–SiO2 Nanoparticles

2017-08-17T07:37:11.110984-05:00

The surfaces of commercially available polyester (PET) and polypropylene (PP) are superhydrophobically modified via the deposition of polydimethylsiloxane (PDMS)-coated SiO2 nanoparticles (P-SiO2) and PDMS binder. The adhesion of P-SiO2 is stronger on PET than on PP due to a stronger chemical interaction between PET and PDMS, which is attributed to the higher surface energy of PET than PP. The waterproof ability and oil separation rate of the P-SiO2-coated PET (dip-PET) membranes are studied as a function of membrane thickness, and the influence of oil viscosity on the oil separation efficiency is investigated. Optimal membrane thickness should be selected in a given environment for the facile oil–water separation and the dip-PET membrane is chemically stable and can be used repetitively for oil–water separation. Finally, an automated prototype instrument is introduced for the dip-coating process. It is suggested that our dip-PET is a promising solution for oil–water separation in real-world oil-spill applications. Superhydrophobically modified polyester (dip-PET) via the deposition of polydimethylsiloxane (PDMS)-coated SiO2 nanoparticles (P-SiO2) using a simple dip-coating method is reported. The equipment consisting of the dip-PET membrane for selective oil-capturing from the water–oil mixture is displayed and an automated prototype instrument for the hydrophobic dip-coating of the fabric samples is demonstrated.



Selective Laser Sintering 3D Printing: A Way to Construct 3D Electrically Conductive Segregated Network in Polymer Matrix

2017-08-01T01:03:00.077311-05:00

Selective laser sintering (SLS), which can directly turn 3D models into real objects, is employed to prepare the flexible thermoplastic polyurethane (TPU) conductor using self-made carbon nanotubes (CNTs) wrapped TPU powders. The SLS printing, as a shear-free and free-flowing processing without compacting, provides a unique approach to construct conductive segregated networks of CNTs in the polymer matrix. The electrical conductivity for the SLS processed TPU/CNTs composite has a lower percolation threshold of 0.2 wt% and reaches ≈10−1 S m−1 at 1 wt% CNTs content, which is seven orders of magnitude higher than that of conventional injection-molded TPU/CNTs composites at the same CNTs content. The 3D printed TPU/CNTs specimen can maintain good flexibility and durability, even after repeated bending for 1000 cycles, the electrical resistance can keep at a nearly constant value. The flexible conductive TPU/CNTs composite with complicated structures and shapes like porous piezoresistors can be easily obtained by this approach. A stretchable and bendable, and electrically conductive polymer nanocomposite with segregated network and designed geometric structure, which is prepared by selective laser sintering, may have potential application in 3D printing of flexible circuit, wearable devices, implantable devices, electronic skin, and dielectric elastomer actuators, etc.



Flexible Polysaccharide Hydrogel with pH-Regulated Recovery of Self-Healing and Mechanical Properties

2017-08-01T01:01:59.290697-05:00

A self-healable hydrogel with recoverable self-healing and mechanical properties is reported. The hydrogel (coded as ACSH) crosslinked by Schiff base linkage contains two polysaccharides of acrylamide-modified chitosan (AMCS) and oxidized alginate (ADA). Self-healing and mechanical properties are heavily influenced by the crosslinking time. The hydrogel crosslinked for 2 h possesses better mechanical and self-healing properties than hydrogel crosslinked for 24 h. Macroscopic test shows that hydrogel without self-healing ability can recover the self-repair and mechanical properties by adjusting the pHs. The recovery of self-healing and mechanical properties relies on the pH sensitivity of the Schiff base linkage. Adjusting the pH to acid, the Schiff base linkage becomes unstable and breaks. Regulating the pH to neutral, reconstruction of Schiff base linkage leads to recovery of the self-repair and mechanical properties. The recoverable self-healing property can be cycled once breakage and reconstruction of the Schiff base linkage can be conducted. In addition, this study demonstrates that the hydrogel can be remodeled into different shapes based on self-healing property of the hydrogel. It is anticipated that this self-healable hydrogel with recoverable self-healing and mechanical properties may open a new way to investigate self-healing hydrogel and find potential applications in different biomedical fields. A flexible biopolymeric hydrogel with recoverable self-healing and mechanical properties is developed. The hydrogel crosslinked by Schiff base linkage contains two polysaccharides of acrylamide-modified chitosan and oxidized alginate. Circular recovery of self-healing and mechanical properties can be realized by adjusting the pHs.



Hydroquinone Based Sulfonated Copolytriazoles with Enhanced Proton Conductivity

2017-08-01T01:01:05.718956-05:00

A series of new fluorinated sulfonated copolytriazoles (PTHQSH-XX) with ion exchange capacity (IECw) values ranging from 1.66 to 2.82 meq g−1 are prepared via cuprous ion catalyzed azide-alkyne click polymerization reaction between 1,4-bis(prop-2-ynyloxy)benzene, 4,4′-diazido-2,2′-stilbene disulfonic acid disodium salt (SA), and 4,4-bis[3′-trifluoromethyl-4′(4-azidobenzoxy) benzyl] biphenyl (QAZ). The degree of sulfonation of the copolytriazoles is adjusted between 60% and 90% by varying the molar ratio of sulfonated monomer (SA) to the nonsulfonated monomer (QAZ). The structure of the copolytriazoles is characterized by Fourier transform infrared and NMR spectroscopy. The solution-cast membranes of these copolymers exhibit high thermal, mechanical, oxidative and hydrolytic stability, and high proton conductivity (19–142 mS cm−1 at 80 °C and 22–157 mS cm−1 at 90 °C). Transmission electron microscopy confirms the formation of good phase separated morphology with ionic clusters in the range of 15–145 nm. A series of fluorinated sulfonated copolytriazoles with high ion exchange capacity are prepared by Cu (I) catalyzed azide-alkyne click polymerization. The membranes prepared from these copolymers exhibit high thermal, mechanical, oxidative and hydrolytic stability, and proton conductivity as high as 142 mS cm−1 at 80 °C.



Tailoring the Morphology of Responsive Bioinspired Bicomponent Fibers

2017-07-25T01:37:09.38309-05:00

Nature is an intriguing inspiration for designing a myriad of functional materials. However, artificial mimicking of bioinspired structures usually requires different specialized procedures and setups. In this study, a new upscalable concept is presented that allows to produce two bioinspired, bicomponent fiber morphologies (side-by-side and coaxial bead-on-string) using the same electrospinning setup, just by changing the employed spinning solvent. The generated fiber morphologies are highly attractive for thermoresponsive actuation and water harvesting. Another challenge solved in this work is the compositional characterization of complex fiber morphologies. Raman imaging and atomic force microscopy is introduced as a powerful method for the unambiguous characterization of complex bicomponent fiber morphologies. The work opens the way for the construction of heterostructured fiber morphologies based on different polymers combinations, offering high potential for applications as actuators, smart textiles, water management, drug release, and catalysis. Tailoring of bioinspired bicomponent fiber structures in a simple way and unambiguous characterization of complex fiber structures by combination of Raman imaging with atomic force microscopy, giving access to promising applications as actuators or for water harvesting, is highlighted.



Tough and Enzyme-Degradable Hydrogels

2017-07-24T07:45:33.356192-05:00

Mechanically robust hydrogels that degrade only via cell action have potential as scaffolds for the generation of load-bearing soft connective tissue. This study demonstrates that terminally acrylated 4-arm-poly(ethylene glycol)-block-oligo(trimethylene carbonate) (4a-PEG-(TMC)n) can be readily reacted with a collagenase-degradable bis-cysteine peptide to form hydrogels. The inclusion of the TMC blocks renders the hydrogels mechanically tough when tested under compression, with modulus and toughness values within the range of those of articular cartilage. Moreover, the hydrogels formed are resistant to degradation by hydrolysis in the absence of collagenase but degrade via surface erosion in the presence of collagenase. The strategy employed to form these hydrogels is readily tailored to create a variety of tough, enzyme-degradable hydrogels of varying mechanical and degradation properties. This paper describes a means of creating an enzyme-degradable hydrogel with mechanical properties approximating those of soft connective tissues such as the articular cartilage and meniscus. These properties are achieved through Michael-type addition crosslinking of a bis-cysteine peptide with a terminally acrylated 4-arm-poly(ethylene glycol) (4a-PEG)-block-oligo(trimethylene carbonate).



Recent Progress of Graphene-Containing Polymer Hydrogels: Preparations, Properties, and Applications

2017-07-20T08:11:37.782177-05:00

Polymer hydrogels have attracted much attention due to their mechanical, biological, and physicochemical properties. Incorporation of functional material enlarges their applications. Graphene, as a promising additive, has received great attention due to its large specific surface area, ultrahigh conductivity, strong antioxidant, thermal stability, high thermal conductivity, and good mechanical properties. In this brief review, graphene-containing polymer hydrogels with special properties are summarized including their preparations, properties, and applications. In addition, future perspectives of polymer hydrogels containing graphene are briefly discussed. Polymer–graphene hydrogels have attracted much attention and introduction of graphene could enable the composite hydrogel with excellent properties in various respects. In this brief review, graphene-containing polymer hydrogels with special properties are summarized including their preparations, properties, and applications. In addition, future perspectives of polymer hydrogels containing graphene are briefly discussed.



Thin Film Nanocomposites Based on SBM Triblock Copolymer and Silver Nanoparticles: Morphological and Dielectric Analysis

2017-07-20T08:01:23.548691-05:00

Hybrid organic/inorganic thin film nanocomposites based on poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate) triblock copolymer and silver nanoparticles are prepared and characterized. In order to improve the compatibility of nanoparticles with the polymeric matrix, their surface is modified with dodecanethiol surfactant, which enables a good dispersion of nanoparticles through the triblock copolymer, without the formation of aggregates. By atomic force microscopy (AFM), the dispersion level of nanoparticles is analyzed, together with their effect on the thin film surface morphology, for nanocomposites up to 15 wt% of nanoparticles. Dielectric properties of nanocomposites are studied by dielectric relaxation spectroscopy (DRS), analyzing the effect of nanoparticles on dielectric properties. Even if conductivity and permittivity of composites increase with nanoparticle content, percolation threshold is found to be at around 15% in volume. Morphologically analyzed nanocomposites are, in this way, below the threshold. Hybrid nanocomposites based on poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate) (SBM) copolymer and surface-modified Ag nanoparticles are prepared and characterized. The dispersion level and effect on SBM film morphology are analyzed, showing that it changes from lamellar to cylinders and spheres by increasing nanoparticle content. The analysis of dielectric properties shows that nanocomposites are below the percolation threshold.



Atmospheric Photopolymerization of Acrylamide Enabled by Aqueous Glycerol Mixtures: Characterization and Application for Surface-Based Microfluidics

2017-07-20T08:00:38.696249-05:00

Polyacrylamide usually is the material of choice for electrophoretic separation in slab gels, capillaries, and microfluidic devices. So far its polymerization requires anaerobic environments because oxygen impurities inhibit or even terminate the polymerization reaction of acrylamide. Here, it is demonstrated that gel precursor solutions with glycerol contents above 20 vol% enable direct atmospheric photopolymerization of acrylamide with no need for sealing or degassing the solution in advance. The positive effect of glycerol on the polymerization reaction is proven by simulation-validated electron paramagnetic resonance measurements. Nuclear magnetic resonance reveals that glycerol does not interfere with the reaction indicating that the observed enhancement in polymerization is owed to the low oxygen solubility of aqueous glycerol mixtures. Glycerol concentrations of >60 vol% in the gel precursor solution enable complete polymerization of volumes down to 5 nL within less than 5 s. This enables using liquid handling robots to fabricate channel-free open microfluidic structures of solid polyacrylamide hydrogel in a low-cost automated manner in a standard lab environment. Nanoliter volumes of aqueous acrylamide–bisacrylamide gel precursor solution including Irgacure 2959 are photopolymerized in presence of atmospheric oxygen using glycerol as an additive. Polymerization times—reduced down to 5 s—and completeness are proportional to the glycerol concentration. The findings allow for the fabrication of microfluidic hydrogel structures by printing the solution followed by selective UV exposure.



Nanocomposites of Polymeric Biomaterials Containing Carbonate Groups: An Overview

2017-07-17T04:02:24.71806-05:00

The modification of biomaterials using nanoadditives can lead to the development of novel materials for a wide variety of biomedical applications such as drug administration systems, tissue engineering, bioresistance coatings, and biomedical instruments. Moreover, a further improvement of mechanical and thermal properties of aforementioned biomaterials while maintaining their dimensional stability is a goal of major scientific researches. Aliphatic polycarbonates (APCs) containing carbonate groups such as poly(trimethylene carbonate), poly(propylene carbonate), poly(ethylene carbonate), poly(dimethyl trimethylene carbonate), etc., have become much more interesting compared to other biodegradable materials due to their unique physical and chemical properties. This review presents the effect of applying different kinds of nanoparticles (NPs) on the mechanical, thermal, and viscoelastic properties as well as dimensional stability and biocompatibility of APCs. The dispersion process of nanofillers within polymer matrices has been divided into two groups, solution and melt mixing techniques. Moreover, synthesis procedures of APC loaded NPs for drug delivery systems and electrospinning of nanofiber mats have also been reviewed. In order to clarify the effect of NPs on the overall characteristics of the APC biomaterials, the detailed mechanism of improving process have been extensively discussed. Aliphatic polycarbonates based on nanocomposites are widely used in drug delivery, tissue engineering, electrolytes and biomedical instruments. One can synthesize these biopolymers by different methods. The nanoparticles can improve the physical and chemical properties of the biopolymers.



In Situ Crosslinking of Highly Porous Chitosan Scaffolds for Bone Regeneration: Production Parameters and In Vitro Characterization

2017-07-10T13:12:11.958028-05:00

Various methods of chitosan scaffold production are reported in the literature so far. Here, in situ crosslinking with glutaraldehyde is reported for the first time. It combines pore formation and chitosan crosslinking in a single step. This combination allows incorporation of fragile molecules into 3D porous chitosan scaffolds produced by simple and gentle lyophilization. In this study, parameters of in situ crosslinking of porous chitosan scaffold formation as well as their effect on degradation and bioactivity of the scaffolds are examined. The scaffolds are characterized in the context of their prospective application as bone substitute material. The addition of calcium phosphate phases (hydroxyapatite, brushite) to the macroporous chitosan scaffolds allows manipulation of the bioactivity that is investigated by incubation in simulated body fluid (SBF). The bioactivity is significantly influenced by the modus of changing the fluid (static, daily-, and twice-a-week change). Scaffolds are morphologically characterized by means of scanning electron microscopy, and the mechanical stability is tested after incubation in SBF and phosphate-buffered saline. Porous chitosan scaffold is produced by in situ crosslinking with glutaraldehyde, combining pore formation and crosslinking in one step. Pore formation and mechanical strength are influenced by chitosan molecular weight and degree of deacetylation, glutaraldehyde concentration, and cooling speed. The addition of calcium phosphate phases to the scaffolds allows manipulation of bioactivity, as well as the liquid change regime.



The Development of Fibers That Mimic the Core–Sheath and Spindle-Knot Morphology of Artificial Silk Using Microfluidic Devices

2017-07-05T12:31:25.37771-05:00

Spider and silkworm produce diverse silk fibers from spinning dopes through smart spinnerets. Spider's capture silk is composed of core thread and periodic spindle-knots, while silkworm silk consists of fibroin core and sericin outer layer. To mimic the morphologies of natural heterostructured silks, artificial fibers are dry-spun using a multichannel microfluidic chip, served with a highly viscous core solution of regenerated silk fibroin and low viscosity sheath solution of sericin. Silk fibers with core–sheath, groove, and spindle-knot structures are obtained by controlling the flow rates and viscosities of the two microfluids depending on the laminar flow, Kelvin–Helmholtz instability, or Plateau–Rayleigh instability. Artificial fibers are dry-spun using a multichannel microfluidic chip, serving with highly viscous core solution of regenerated silk fibroin and lowly viscous sheath solution of sericin. The core–sheath, groove, and spindle-knots structures of the fibers can be manipulated by controlling the flow rates and viscosities of the two microfluids.



Immersion Electrospinning as a New Method to Direct Fiber Deposition

2017-07-05T07:42:42.515096-05:00

This paper describes a new method for directed steering of fibers via a combination of electro- and wet-spinning: Immersion Electrospinning. In this process, a polymeric dope is extruded directly into a coagulation bath (e.g., a blend of chloroform/mineral oil). Through increased drag force and reduced charge build-up on the fiber surface, the speed of the fiber jet, driven by an electric field, is greatly reduced in comparison to traditional electrospinning. This speed reduction coincides with suppression of the whipping motion, offering better control of jetting behavior. Immersion Electrospinning of poly(acrylonitrile), PAN, at five different electric fields ranging from 12.5 to 375 kV m−1 shows continuous fiber formation until a critical electric field strength, Ecrit = 125 kV m−1. At Ecrit, an increased whipping motion is observed and above Ecrit, fiber disruption and fragmentation occur. Selectively applying ≈50 kV m−1 to an array of electrodes produces a continuous PAN fiber in a square path. Immersion Electrospinning, a new method, combines electro- and wet-spinning. A stationary needle submerged in a coagulation bath reduces fiber speed and mitigates bending instabilities found in traditional electrospinning. With selective application of voltage to electrodes, fibers are steered through the bath. By altering the configuration and quantity of electrodes, fibers have the potential to be directed into endless designs.



Dual-Crosslinked Human Serum Albumin-Polymer Hydrogels for Affinity-Based Drug Delivery

2017-07-05T07:37:22.1839-05:00

A dual-crosslinked in situ gelling drug delivery scaffold based on dextran (DEX), thiolated serum albumin, and poly(ethylene glycol) (PEG) is presented. Dextran–vinyl sulfone conjugates with varied molecular weight and degrees of substitution are synthesized by controlling the reaction time and temperature with divinyl sulfone. Dextran–human serum albumin (sHSA) hydrogels are prepared using a thiol-vinyl sulfone Michael addition reaction with thiolated albumin as the crosslinker. Poly(ethylene glycol) dithiol is added as a third component to the crosslinked dextran–human serum albumin hydrogel to facilitate additional crosslinking, and reduce gelation time, while modulating the physicochemical properties of the Dex–sHSA–PEG network. The onset of gelation of the modular three-component dual-crosslinked hydrogel network ranges from 45 min to 1.5 h depending on gel constituent concentrations and the gelation temperature (25 or 37 °C). All gels remain stable for over a 25 d period under physiological conditions. In vitro drug release assays show that dual-crosslinked Dex–sHSA–PEG hydrogels can deliver doxorubicin in a sustained manner over 7 d. Finally, a Tetrazolium-based assay shows the biocompatible nature of the Dex–sHSA–PEG hydrogels and capacity to deliver doxorubicin successfully to MCF-7 breast cancer cells. A novel and stable dual-crosslinked affinity-based drug delivery system based on dextran, human serum albumin, and poly(ethylene glycol) is reported. This hydrogel drug delivery system can be flexibly prepared using thiol-vinyl sulfone Michael addition. By utilizing human serum albumin as an affinity-based drug carrier in this material, a chemotherapeutic can be delivered to MCF-7 human breast cancer cells.



UV-Printable and Flexible Humidity Sensors Based on Conducting/Insulating Semi-Interpenetrated Polymer Networks

2017-07-05T07:23:21.696082-05:00

Humidity sensors are of great interest in many fields because humidity plays a crucial role in several processes. Nevertheless, their application is often limited by the expensive fabrication and the stiffness of the substrates usually employed. In this work, novel UV-curable and flexible humidity sensors based on semi-interpenetrated polymer networks are fabricated. They can be prepared either as self-standing sensors or applied on different bendable substrates. The fabrication consists of a simultaneous UV-curing of an insulating network (acrylic or epoxy) and photopolymerization of conducting polypyrrole (PPy). The detection mechanism involves proton transfer on the PPy chains that can be macroscopically observed by electrical impedance variations. These devices show promising humidity-sensing properties from 20 to 97% of relative humidity with a maximum response of about 180%. The dynamic sensing investigation proves that the recovery process can be tailored playing on the glass transition temperature and wettability of the films. The remarkable sensing capabilities of these sensors make them a valid alternative in many applications where printability and flexibility are required along with simple fabrication method consisting of one-step synthesis. Novel UV-curable and flexible humidity sensors based on semi-interpenetrated polymer networks are fabricated. These devices show promising humidity-sensing properties from 20 to 97% of relative humidity with a maximum response of about 180%.



Silver Nanoparticles Loaded Thermoresponsive Hybrid Nanofibrous Hydrogel as a Recyclable Dip-Catalyst with Temperature-Tunable Catalytic Activity

2017-07-05T07:22:56.140697-05:00

Silver nanoparticles (AgNPs) loaded thermoresponsive nanofibrous hydrogel is fabricated by electrospinning the aqueous solution containing the metal nanoparticles and poly((N-isopropylacrylamide)-co-(N-hydroxymethylacrylamide)) copolymer, followed by heat treatment. To avoid negative effect of the stabilizer or the residual reductant on their performances, the AgNPs of less than 5 nm size are synthesized through reducing Ag+ ions in the spinning solution by UV irradiation. The prepared nanofibrous hydrogel with desirable stability in aqueous medium has significant thermoresponsive property, and can reach its swelling or deswelling equilibrium state within 15 s with the medium temperature changing between 25 and 50 °C alternately. The smart nanofibrous hydrogel as a dip-catalyst has the catalysis for the reduction of 4-nitrothiophenol to 4-aminothiophenol by NaBH4, and its catalytic activity can be rapidly tuned by temperature. Moreover, it can be facilely recycled from the reaction system at least four times, without any loss of its catalytic activity. Silver nanoparticles synthesized by in situ reducing Ag+ ions in the spinning solution upon exposure of ultraviolet irradiation are loaded into thermoresponsive nanofibers by electrospinning technique, followed by heat treatment. The formed smart hybrid nanofibrous hydrogel with high stability in aqueous medium is able to be used as a recyclable dip-catalyst with temperature-tunable catalytic activity.



Cellulose-Derived Carbon Fibers with Improved Carbon Yield and Mechanical Properties

2017-07-05T07:22:22.586945-05:00

The manufacture of high mechanical strength cellulose-based carbon fibers (CFs) is accomplished in a continuous process at comparably low temperatures and with high carbon yields. Applying a sulfur-based carbonization agent, i.e., ammonium tosylate (ATS), carbon yields of 37% (83% of theory), and maximum tensile strengths and Young's moduli up to 2.0 and 84 GPa are obtained already at 1400 °C. For comparison, the use of the well-known carbonization aid ammonium dihydrogenphosphate ((NH4)H2PO4), ADHP, is also investigated. Both the precursor and the CFs are characterized via elemental analysis, wide-angle X-ray scattering, Raman spectroscopy, scanning electron microscopy, and tensile testing. Thermogravimetric analysis coupled with mass spectrometry/infrared spectroscopy discloses differences in structure formation between ATS and ADHP-derived CFs during pyrolysis. High mechanical strength cellulose-based carbon fibers (CFs) are prepared in a continuous process at comparably low temperatures and with high carbon yields. With a sulfur-based carbonization agent, carbon yields of 37 wt% (83% of theory) and maximum tensile strengths and Young's moduli up to 2.0 and 84 GPa, respectively, are obtained at 1400 °C.



Microstructural Evolution of Isotactic-Polypropylene during Creep: An In Situ Study by Synchrotron Small-Angle X-Ray Scattering

2017-07-04T07:42:43.307793-05:00

The structure evolution of isotactic-polypropylene during creep is investigated by in situ synchrotron small-angle X-ray scattering. During primary creep, strain grows nonlinearly to a value less than 15%. The long period in loading direction (L∥) increases with time, whereas the long period perpendicular to the loading direction (L⊥) decreases slightly. During the secondary creep, strain increases linearly with time. L∥ and L⊥ show the same tendency with strain. The increase of the long period is caused by lamellae thickening, which is a kind of cooperative motion of polymer chains with their neighbors at the lamellae surface. Moreover, the growth rate of L∥ is larger than that of L⊥, indicating that the orientation of molecular chains along the loading direction decreases the energy barrier of the cooperative motion. During tertiary creep, strain grows dramatically in a short time. In this step, the lamellae are tilted, rotated, and then disaggregated. In addition, a fibrillar structure is formed during lamellae breaking. The length of the fibrillar structure increases from 364 to 497 nm while its width stays at 102 nm with increasing creeping time. The microstructural evolution during creep can be well distinguished into four stages. During secondary creep, lamellae thickening can be found. The lamellae thickening rate along the loading direction is higher than that perpendicular to the loading direction. After yielding, the fibrillary structure can be induced by lamellae breaking and reorganization. The length of the fibrillary structure increases from 364 to 497 nm, whereas its width stays at 102 nm as creep time increases.



Shrinkage and Warpage Optimization of Expanded-Perlite-Filled Polypropylene Composites in Extrusion-Based Additive Manufacturing

2017-07-04T07:41:55.89006-05:00

A major challenge in extrusion-based additive manufacturing is the lack of commercially available materials compared to those in well-established processes like injection molding or extrusion. This study aims at expanding the material database by evaluating the feasibility of polypropylene, which is one of the most common and technologically relevant semicrystalline polymers. Expanded-perlite-filled polypropylene and ternary blends with amorphous polyolefins are evaluated to establish an understanding of their processability and their printability. A detailed study on the shrinkage behavior, as well as on the thermal, mechanical, morphological, and warpage properties is performed. It is found that smaller sized fillers result in a tremendous warpage and shrinkage reduction and concurrently improved mechanical properties than compounds filled with bigger sized fillers. Based on the optimal properties profile, a ternary blend that can overcome the shrinkage and warpage of printed parts is suggested. The semicrystalline nature of polypropylene usually results in undesirable shrinkage and warpage, especially when parts are produced by extrusion-based additive manufacturing. The present work aims at addressing this issue by offering a simple strategy for producing dimensionally stable 3D-printed polypropylene. Therefore, ternary blends containing amorphous polyolefins and spherical perlite fillers are compounded, characterized, and successfully printed.



Hierarchical Self-Assembly of Poly(Urethane)/Poly(Vinylidene Fluoride-co-Hexafluoropropylene) Blends into Highly Hydrophobic Electrospun Fibers with Reduced Protein Adsorption Profiles

2017-07-03T01:45:39.466598-05:00

Electrospinning of blend systems, combining two or more polymers, has gained increasing interest for the fabrication of fibers that combine properties of the individual polymers. Here, a versatile method to produce hydrophobic fibers composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDFhfp) and polyurethane (PUR) is presented. PVDFhfp containing fibers are expected to reduce protein adsorption. In a one-step process, blend solutions are electrospun into homogeneous nonwoven membranes with fiber diameters in the range of 0.6 ± 0.2 to 1.4 ± 0.7 µm. Surface fluorine concentrations measured by X-ray photospectroscopy show an asymptotic dependency in function of the PVDFhfp to PUR ratio, reaching values close to pure PVDFhfp at a weight per weight ratio of 10% PVDFhfp to 90% PUR. This fluorine enrichment on the surface suggests a gradient structure along the fiber cross-section. At increased surface fluorine concentration, the contact angle changes from 121 ± 3° (PUR) to 141 ± 4° (PUR/PVDFhfp). Furthermore, these highly hydrophobic fibers present significantly reduced fibrinogen or albumin adsorption compared to PUR membranes. The formation of fibrous membranes with fluorine enriched surfaces for biomedical applications is reported. Polymer blends of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDFhfp) and polyurethane (PUR) are processed into bi-component fibers by electrospinning. At a 20 wt% ratio of PVDFhfp to PUR, fibers display chemical surface properties comparable to pure PVDFhfp fibers, along with reduced protein adsorption compared to PUR fiber.



A Sponge-Like 3D-PPy Monolithic Material for Reversible Adsorption of Radioactive Iodine

2017-06-30T07:39:26.609676-05:00

3D polypyrrole (3D-PPy) monolith is prepared by a simple chemical oxidation of pyrrole monomer using FeCl3 as an oxidant. The as-prepared PPy monolith exhibits an abundant porosity and with a mesopore size of about 9.1 nm in diameter. Taking advantage of its mesoprous feature as well as the unique chemical composition, the 3D-PPy is employed as the porous medium for adsorption and removal of radioactive iodine from environment. A high iodine adsorption capacity of 1.6 g g−1 for 3D-PPy is obtained which is competing with that of those reported porous organic polymers. Besides, the adsorption kinetics and adsorption thermodynamic experiments show that the adsorption is dominated by the pseudosecond-order kinetics and Langmuir models. Considering its simple and low cost-effective preparing method, unique monolithic porous as well as π–π conjugated chemical structure, the resulted 3D-PPy may be found useful applications for removal of radioactive iodine to address environmental issues. A sponge-like 3D-polypyrrole (PPy) monolithic material is prepared by chemical oxidation of pyrrole monomer using FeCl3 as an oxidant. The as-prepared PPy exhibits a relative high specific surface area of 16 m2 g−1. Moreover, the low cost-effective preparing method and its abundant pore structure as well as the unique chemical compositions making it an ideal candiate for adsorption of radioactive iodine.



Direct Printing of Thermal Management Device Using Low-Cost Composite Ink

2017-06-30T07:21:38.256233-05:00

This work presents a new method for fabricating thermal devices, such as heat sinks, using a 3D printing technique and lightweight composite ink. The method focuses on formulating composite inks with desired properties and direct ink writing for manufacturing. The ink undergoes two phases: phase one uses low viscosity epoxy to provide viscoelastic properties and phase two provides the fillers consisting of carbon fiber and graphite nanoplatelets to provide high thermal conductivity and structural properties. By combining these functional materials, 3D structures with a high thermal conductivity (≈2 W m−1 K−1) are printed for thermal management applications with the storage modulus of 3000 MPa and a density only 1.24 g cm−3. The results show that by carefully tailoring functional properties of the ink, net-shape multifunctional structures can be directly printed for thermal management device applications, such as heat sinks. Light weight and low-cost thermal devices such as heat sink are fabricated using direct ink printing of epoxy with hybrid filler including carbon fiber and graphite nanoplatelets. Printed structure shows good thermal conductivity of 2 W m−1 K−1. This work can open new methods to fabricate low cost and high performance thermal devices.



Dual-Crosslinking of Hyaluronic Acid–Calcium Phosphate Nanocomposite Hydrogels for Enhanced Mechanical Properties and Biological Performance

2017-06-30T07:21:13.877874-05:00

Herein, a facile approach for synthesizing mechanically enhanced nanocomposite hydrogels via a dual-crosslinking process is described. Additional ionic crosslinking using various cations is introduced after an in situ precipitation process for hydroxyapatite immobilization in hyaluronic acid hydrogels (HAc–CaP). Ca2+, Ba2+, and Sr2+ ions exhibit the highest efficiencies in reinforcing the mechanical properties of HAc–CaP hydrogels. In addition, the dual-crosslinked HAc–CaP hydrogels promote the biological responses of preosteoblast cells, which exhibit highly stretched shapes and greatly enhanced proliferation. Furthermore, the nanocomposite hydrogels achieve enhanced bioactivity by supporting osteogenic differentiation. Thus, enhancement on both the mechanical and biological properties of hyaluronic-acid-based nanocomposite hydrogels is achieved through this dual-crosslinking process, extending the potential application of these materials to hard tissue engineering. Additional ionic crosslinking using various cations (especially Ca2+, Ba2+, and Sr2+ ions) after an in situ precipitation process for hydroxyapatite immobilization in hyaluronic acid hydrogels greatly enhances not only the mechanical properties but also biological performance.



Photocatalytic Activity of Titania/Polydicyclopentadiene PolyHIPE Composites

2017-06-30T07:20:38.523095-05:00

Macroporous polymer composites with photocatalytic activity are prepared by the polymerization of surface modified TiO2 nanoparticle stabilized high internal phase emulsions. Poly(ethylene glycol-b-propylene glycol-b-ethylene glycol) triblock copolymer is used to synthesize surface modified TiO2 anatase via a sol–gel method. Macroporous composites are obtained by the ring opening metathesis polymerization of dicyclopentadiene within the particle-stabilized high internal phase emulsion templates. Photocatalytic activity of the resulting macroporous polymer composites is described by the kinetic data of the heterogeneous photocatalytic degradation reaction of 4-nitrophenol. Titania anatase particles and polydicyclopentadiene polymer combined within high internal phase emulsion form highly porous composite material of which a photocatalytic activity is demonstrated by the oxidation of 4-nitrophenol.



Transparent Conducting Electrodes from Conducting Polymer Nanofibers and Their Application as Thin-Film Heaters

2017-06-30T07:17:36.659563-05:00

Transparent conducting electrodes attract attention in relation to solar cells, touch panels, displays, e-readers, and transparent heaters. In many cases, rarefied metal nets with optical transmittance of ≈90% and with minimal sheet resistance are sought after. Here, a mesh of conducting polymer nanofibers is developed as a transparent conducting electrode. A sheet resistance of 8.4 kΩ sq−1 with 84% optical transmittance is achieved with polyethylene oxide/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEO/PEDOT:PSS) blended polymer nanofibers. This study also demonstrates that such nanofiber being deposited on a glass substrate can be used as a transparent film heater in relevant applications such as window heating or displays at harsh environments. Such a transparent heater is rated at 0.41 W in.−2 for 120 V. It is also capable of heating a substrate up to ≈70 °C in 4 min at 60 V from room temperature without any degeneration of nanofiber network, rendering itself as a practically useful transparent heater. The performance of the PEO/PEDOT:PSS nanofiber-coated transparent glass heater is comparable to that of the relatively expensive indium tin oxide thin-film heaters. Transparent conducting electrode based on conducting polymer nanofibers is developed with a sheet resistance of 8.4 kΩ sq−1 and the 84% optical transmittance. Being deposited on a glass substrate, such electrodes can be used as transparent film heaters for window heating, and are capable of heating a substrate up to ≈70 °C in 4 min at 60 V from room temperature.



Stabilization Mechanism of Micropore in High-Density Polyethylene: A Comparison between Thermal and Mechanical Pathways

2017-06-30T07:15:37.787934-05:00

Aiming to reveal the stabilization mechanism of micropore embryos formed during cold stretching in high-density polyethylene films, samples are subsequently subjected to temperature elevation and strain holding at 25 °C, respectively. The corresponding structure evolution is tracked. It is found that after strain holding at 25 °C and subsequent strain recovery, inhomogeneously distributed cavities are produced, most of which can be healed as temperature is elevated to 110 °C. Consequently, only a small number of nonevenly distributed micropores are formed during the subsequent hot stretching. While for thermal pathway, micropores and fibrils can be formed as temperature is elevated. The hot stretching membrane exhibits uniformly distributed micropores and the micropores are well interconnected, indicating that micropores stabilized via temperature elevation are permanent and homogeneous. The results reveal different stabilization mechanisms of micropores via the thermal and mechanical pathways with regard to the distribution as well as the amount of permanent micropores. Stabilization mechanisms of micropore embryos formed during cold stretching in high-density polyethylene films are investigated via temperature elevation and strain holding at 25 °C, respectively. The thermal and mechanical pathways take different effects not only on the uniformity of micropore evolution, but also on the amount of stable micropores at elevated temperature.



Macromol. Mater. Eng. 9/2017

2017-09-13T13:38:55.072409-05:00

Front Cover: Mechanically robust, tough and self-recoverable hydrogels are fabricated by molecularly engineering fully flexible crosslinking points of triblock copolymer micelles, ionic interactions, hydrogen bonds, etc. This is reported by Hongwei Zhou, Xilang Jin, Bo Yan, Xingjian Li, Wen Yang, Aijie Ma, Xiaohui Zhang, Ping Li, Xiaobin Ding and Weixing Chen, in article number 1700085.



Masthead: Macromol. Mater. Eng. 9/2017

2017-09-13T13:38:58.33154-05:00




Contents: Macromol. Mater. Eng. 9/2017

2017-09-13T13:38:59.852426-05:00




Thermal Properties of Graphene Filled Polymer Composite Thermal Interface Materials

2017-05-18T02:51:33.290482-05:00

Recent years have witnessed a staggering escalation in the power density of modern electronic devices. Because increasingly high power density accumulates heat, efficient heat removal has become a critical limitation for the performance, reliability, and further development of modern electronic devices. Thermal interface materials (TIMs) are widely employed between the two solid contact surfaces of heat sources and heat sinks to increase heat removal for electric devices. Composites of graphene and matrix materials are expected to be the most promising TIMs because of the remarkable thermal conductivity of graphene. Here, the recent research on the thermal properties of graphene filled polymer composite TIMs is reviewed. First, the composition of graphene filled polymer composite TIMs is introduced. Then, the synthetic methods for graphene filled polymer composite TIMs are primarily described. This study focuses on introducing the methods for improving and characterizing the thermal properties of graphene filled polymer composite TIMs. Furthermore, the challenges facing graphene filled poly­mer composite TIMs for thermal management applications in the modern electronic industry and the further progress required in this field are discussed. This review introduces the composition, the synthetic methods, the methods for improving, and characterizing the thermal properties of graphene filled poly­mer composite thermal interface materials (TIMs). And discusses the challenges facing graphene filled polymer composite TIMs for thermal management applications in the modern electronic industry and the further progress required in this field.



3D Printing of Polymer Nanocomposites via Stereolithography

2017-05-22T08:00:29.311412-05:00

Additive manufacturing (AM) is still underutilized as an industrial process, but is quickly gaining momentum with the development of innovative techniques and materials for various applications. In particular, stereolithography (SLA) is now shifting from rapid prototyping to rapid manufacturing, but is facing challenges in parts performance and printing speed, among others. This review discusses the application of SLA for polymer nanocomposites fabrication to show the technology's potential in increasing the applicability of current SLA-printed parts. Photopolymerization chemistry, nanocomposite preparation, and applications in various industries are also explained to provide a comprehensive picture of the current and future capabilities of the technique and materials involved. Stereolithography as a 3D printing technique for fabricating polymer nanocomposites is reviewed. Focus is given on variations of the technique, material preparation prior to printing, chemistry during printing, and current and potential applications of the technology.



Intelligent Nanofiber Composites: Dynamic Communication between Materials and Their Environment

2017-05-26T12:12:40.572854-05:00

Intelligence of living and nonliving systems is often characterized by the ability to communicate through signal and response. In the polymer science community, this intelligence is realized through the reaction of a material construct to environmental triggers. These smart materials are modeled after natural materials, which utilize matrix–fiber architectures to detect stimuli, release small molecules, or alter their macroscopic morphology in response to stimuli. As such, researchers have designed matrix–fiber composites, which function as release vehicles, sensors or switches, and actuators. Through the examination of the architecture and environmental triggering of these natural muses, the fundamental design parameters necessary for functional response in matrix–fiber composites and the ability to utilize these composites in targeted applications are highlighted. Opportunities for innovation in composite design are also discussed. Intelligent matrix–fiber composites take advantage of hierarchical structures to interact with their environment. In nature, stimuli-responsive behavior is demonstrated by living systems like the human extracellular matrix, the Dynastes Hercules beetle, and Pinus seed pods. Utilizing these examples as inspiration, scientists are able to design a variety of composite platforms that act as release vehicles, sensors or switches, and actuators.



Enhanced Optical Transmittance by Reduced Reflectance of Curved Polymer Surfaces

2017-05-26T01:10:52.561778-05:00

Subwavelength nanostructure arrays on surfaces improve their optical transmittance by reducing the reflection of light over a wide range of wavelengths and angles of incidence. A method to imprint a sub-100 nm nanostructure array on a large surface (Ø 20 mm) made from thermoplastic materials is reported. Transmittance through the flat polymer is improved by ≈6.5%, reaching values of up to 97.5%, after imprinting. The optical properties of the nanostructured samples are highly reproducible. After eight repeated imprinting operations with the same stamp, the transmittance of the nanostructured surface is decreased by less than 0.2%. Moreover, the nanostructures can also be imprinted on curved polymethylmethacrylate surfaces, achieving a maximum transmittance of 97%. This method to prepare large-scale antireflective nanostructures on flat and flexible curved polymer surfaces is of interest for the production of antireflective screens, optical devices, and biomedical devices such as contact lenses and intraocular lenses. A subwavelength nanostructure array is imprinted on a large thermoplastic material surface. Excellent antireflective properties over a wide range of wavelengths and angles of incidence are measured. The nanostructures can also be imprinted onto a flexible, curved surface. The fidelity of the nanostructured pattern is kept intact during the transfer and the resulting surfaces achieve high optical transmittance.



Mechanically Robust, Tough, and Self-Recoverable Hydrogels with Molecularly Engineered Fully Flexible Crosslinking Structure

2017-05-16T07:25:34.652146-05:00

How to reasonably fabricate polymer network for high performance hydrogels is a critical issue but remains a challenge. This work reports an approach to high performance hydrogels by molecularly engineering fully flexible crosslinking (ffC) network. A model network cross-linked by fully flexible crosslinking points of triblock copolymer micelles and ionic interactions is fabricated. Due to the unique structure, the resulting ffC hydrogels are mechanically robust, tough, and self-recoverable. For as-prepared ffC hydrogels, a tensile stress more than 3.5 MPa can be achieved and the energy dissipation can reach up to 6.61 MJ m−3 at the tensile strain of 125%. Moreover, ffC hydrogels fabricated under constant strain can achieve an energy dissipation ability up to 11.63 MJ m−3 at the tensile strain of 100% and a tensile stress of 17.57 MPa. Based on these results, a dynamic molecular mechanism in the ffC hydrogel network under tensile deformation is proposed. The high performances of the ffC hydrogels can be possibly attributed to the sequential breakage and energy dissipation of the flexible crosslinking points and the easily accessible polymer chain orientation during tensile deformation. Mechanically robust, tough, and self-recoverable hydrogels are fabricated by molecularly engineering fully flexible crosslinking network. This strategy provides not only an alternative clue to fabricate soft but robust artificial materials, but also a platform to integrate extraordinary mechanical properties into one hydrogel network.



The Complexation between Amide Groups of Polyamide-6 and Polysulfides in the Lithium–Sulfur Battery

2017-05-19T06:20:44.595759-05:00

Lithium–sulfur batteries have attracted considerable attention due to its high theoretical specific capacity, low cost, environmental friendliness, etc. However, the dissolution of polysulfide intermediate in the electrolyte leads to rapid capacity decay in the charge–discharge process. A sulfur-based cathode with the specific discharge capacity of 630 mAh g−1 and ultrahigh capacity retention ratio of 0.11% per cycle after 400 cycles at 0.5 C that simply blend the sublimed sulfur and acetylene black in the mortar with the polyamide-6 (PA6) as binder is reported. The intense complexation between the lithium polysulfide and amide groups (CONH) in PA6 can effectively inhibit the “shuttling effect” and reduce the loss of active materials during the charge–discharge process. The discovery provides a handy and practicable strategy for developing the excellent cycling stability lithium–sulfur batteries. During the charge–discharge process of lithium–sulfur batteries, S or Li2S2/Li2S cathodes go through a series of intermediate polysulfides and become Li2S2/Li2S or S. The complexation between the lithium polysulfides and the amide groups inhibits the “shuttle” of lithium polysulfides when S or Li2S2/Li2S transform to the soluble lithium polysulfides during the discharge process, preventing the loss of active materials.



Composite Membrane Formation by Combination of Reaction-Induced and Nonsolvent-Induced Phase Separation

2017-05-24T08:55:36.333632-05:00

A novel method of preparing skinned asymmetric membranes with two distinctive layers is described: a top layer composed of chemically cross-linked polymer chains (dense layer) and a bottom layer of non-cross-linked polymer chains (porous substructure). The method consists of two simple steps that are compatible with industrial membrane fabrication facilities. Unlike conventional processes to prepare asymmetric membranes, with this approach it is possible to finely control the structure and functionalities of the final membrane. The thickness of the dense layer can be easily controlled over several orders of magnitude and targeted functional groups can be readily incorporated in it. Novel method of preparing skinned asymmetric membranes with two distinctive layers is described: a top layer composed of chemically cross-linked polymer chains (dense layer) and a bottom layer of non-cross-linked polymer chains (porous substructure). With this approach it is possible to tune the structure and functionalities of the final membrane as well as control the thickness of the dense layer.



Ultralight and Flexible MWNTs/Polyimide Hybrid Aerogels for Elastic Conductors

2017-06-30T07:37:37.389676-05:00

Aerogels have showed tremendous potential applications because of its unique and outstanding properties. Herein, a novel two-step approach to form self-assembly nanocomposite aerogels driven by the strong interactions between water-soluble polyimide (PI) precursor polyamic acid salt (PAAs) and hydroxyl multiwalled carbon nanotubes (MWNTs-OH) is reported. The PI therein constitutes the framework of the nanocomposite and raises the strength of the cell walls, which endows aerogels with superelasticity and robustness. The MWNTs-OH is distributed uniformly into water via physical ultrasonic method followed by blending with PAA molecular. During the imidization process, electrically insulating polyamic acid (PAA)/MWNTs-OH aerogels are converted to conductive PI/MWNTs-OH nanocomposite aerogels owning to the removal of their oxygenic functional groups of OH functionalized MWNTs. Moreover, adding multi-walled carbon nanotube (MWNTs) contributes to the reduction of shrinkage notably, which can be evidenced by scanning electron microscopy measurement and density data. The nanocomposite aerogels display a high elastic modulus, high compressive stress, superior robustness, and high stress-sensitive electrical conductivity. Interestingly, the variation trend of the electric resistance with compressive strain (R/R0–ε) plots is consistent with the compressive stress–strain (σ–ε) curves, which can be explained by the “interface contact spots” theory. And this finding could facilitate the development of polymer-based nanocomposite aerogels as elastic conductors for various applications. The introduction of hydroxyl multi-walled carbon nanotubes (MWNTs-OH) reduces the shrinkage and cost notably, endows the nanocompoiste with stress-sensitvity. The three characteristic regions can be identified in loading-unloading curve of PI-80 nanocomposite clearly. Interestingly, the variation trend of the electric resistance with compressive strain plots is consistent with the loading-unloading curve, which shows great potential for various applications.



Extreme Toughness Exhibited in Electrospun Polystyrene Fibers

2017-06-26T07:12:57.986811-05:00

Polystyrene (PS) commonly exhibits brittle behavior and poor mechanical properties due to the presence of structural heterogeneities promoting localized failure. The removal of this localized failure is shown here by processing PS into fibers with a range of diameters using electrospinning. Mechanical properties of individual electrospun fibers were quantified with atomic force microscopy based nanomechanical tensile testing. The resultant stress–strain behavior of PS fibers highlights considerable enhancement of mechanical properties when fiber diameter decreases below 600 nm such that polystyrene toughness increases significantly by over two orders of magnitude compared to the bulk. Consideration of the network properties of polystyrene is used to demonstrate the increase of draw ratio toward a theoretical limit and is potentially applicable to a range of glassy polymeric materials. Polystyrene (PS) is a potentially robust and high toughness plastic. PS commonly exhibits brittle behavior and poor mechanical properties due to the presence of structural heterogeneities promoting localized failure. Mechanical tensile testing of individual electrospun PS fibers demonstrates considerable enhancement of mechanical properties, including toughness increases of over two orders of magnitude compared to the bulk.



Quarternized Short Polyethylenimine Shows Good Activity against Drug-Resistant Bacteria

2017-06-30T07:16:33.470478-05:00

The rise in resistant bacteria strains worldwide is proving to be a challenge to the healthcare industry. These “superbugs” are emerging faster than the rate of new antibiotic discovery. This has a heavy impact on medical devices as they are susceptible to biofilm production. Antimicrobial resistance (AMR) causes infections to be difficult to treat, especially postimplantation of a medical device. To prevent bacterial adhesion on devices, various types are coatings are introduced. By binding antibiotics to polymers, an effective adhesive coating on the surface can be created. However, with AMR on the rise, these polymers are losing their efficacy in the application. Another class of antimicrobial polymers with a different mode of mechanism will be explored in this project. Biocidal polymers are effective antimicrobial agents as they rely on the electrostatic interactions between the polymeric charged groups and the charged microbial membrane. Polyethylenimine (PEI) can be modified to achieve a macromolecule containing various charged cationic groups. Quaternizing low-molecular-weight PEI with different alkyl groups of short, long, and aromatic groups will give rise to various structural differences. The structure of the quaternized PEI is characterized, and its antimicrobial activity and compatibility are shown to be remarkably improved. Quaternizing low molecular weight polyethylenimine (PEI) with different alkyl groups of short, long, and aromatic groups will give rise to various structural differences. The structure of the quaternized PEI is characterized and its antimicrobial activity and compatibility are shown to be remarkably improved.



pH-Responsive Polymer Coatings for Reporting Early Stages of Metal Corrosion

2017-05-22T01:45:56.075346-05:00

Many systems benefit from the ability to autonomously signal the occurrence of damage. The development of smart polymer coatings on metals can address scientific challenges such as nondestructive detection of early corrosion to avoid further destruction of materials. Here, pH-responsive polymer coatings on metals such as steel, aluminum, magnesium, and copper alloys are reported. The defect areas of coatings can gradually exhibit strong fluorescence as the corrosion starts. Based on the fundamental understanding of electrochemical mechanisms in metal corrosion, the designed pH-responsive polymer coating is dormant before crack occurrence. However, the on-demand release of fluorescent molecules from nanocontainers in coatings occurs as corrosion proceeds with increasing pH value by transformation into highly active fluorescence indication from the dormant state at the stage of corrosion commencement. The developed smart polymer coatings can report the corrosion caused by a coating failure which provides a new strategy for nondestructive corrosion detection. Smart polymer coatings on metals can address scientific challenges such as nondestructive detection of early corrosion to avoid further destruction of materials. Here, pH-responsive polymer coatings on metal surfaces such as steel, aluminum, magnesium, and copper alloy which are capable of self-reporting of early corrosion are reported.



Self-Healing Epoxy Coatings via Focused Sunlight Based on Photothermal Effect

2017-05-22T08:00:43.554052-05:00

Epoxy coatings which can be healed via photothermal effect from focused sunlight are reported. The diamine of m-xylylenediamine (MXDA) and monoamine of 4-(heptadecafluorooctyl)aniline (HFOA) are reacted into the diglycidylether of bisphenol A (DGEBA) network. Via gradual replacement of MXDA with HFOA, the glass transition temperature and crosslinking density of the epoxy network are tuned to achieve the thermally induced healing based on chain diffusion and reentanglement. Aniline black (AB) with well absorptivity for sunlight is used subsequently as the organic photothermal compound, transferring the thermally induced healing into a sunlight responsive one. A common handheld magnifier, which can focus natural sunlight to the required power density (0.6–0.9 W cm−1), is used to successfully heal one cracked coating in outdoor circumstance. This study provides a potential approach to achieve the convenient, precise, and timely healing for outdoor epoxy coatings. Focused sunlight responsive epoxy self-healing coatings are prepared. The ratio of diamine and monoamine is tuned to achieve the well thermally induced self-healing, while aniline black is used to offer the photothermal effect and sunlight trigged self-repairing. A potential approach to achieve the convenient, precise, and timely healing for outdoor epoxy coatings is provided.



PDMS Deposition for Optical Devices by Dip-Pen Nanolithography

2017-05-26T01:10:46.373856-05:00

Dip-pen nanolithography (DPN) is a low-cost, versatile bench-top method for directly patterning materials on surfaces with sub-50 nm resolution; it involves the use of a cantilever tip to transfer a selected ink onto various surfaces to create predefined patterns. Many parameters may influence DPN quality, due to the variety of deposited and surface materials and the chemical interactions between them. DPN tip deposition of liquid inks is not yet well understood, due to the lack of thorough study of the various parameters that need to be controlled in order to achieve uniform patterning. In this research, the printing of polydimethylsiloxane (PDMS) lines and the control of their physical dimensions are investigated; the applied parameters are different humidity levels, n-hexane dilution proportions and different tip velocities. Numerous experiments accompanied by atomic force microscope measurements are conducted in order to derive a recommended recipe for the required dimensions of the printable lines. A practical aspect of the research is to assess the potential of the application of DPN for the fabrication of various optical devices, such as gratings and waveguides. In order to validate the theoretical results, PDMS printing over silicon is used to successfully produce an optical diffraction grating. The performance of dip-pen nanolithography is studied. The dependence of the line width of the deposited polydimethylsiloxane ink on cantilever tip velocity, ambient relative humidity, and percentage of hexane diluting the ink is demonstrated. Extensive experimental results are displayed. The technology is discussed in the context of optical components fabrication.



Engineering Porous Water-Responsive Poly(PEG/PCL/PDMS Urethane) Shape Memory Polymers

2017-07-03T01:51:43.205419-05:00

Porous and bulk water-responsive urethane-based shape memory polymers (SMPs) containing poly(ethylene glycol) (PEG), poly(caprolactone), and poly(dimethylsiloxane) are fabricated. The copolymers are processed by electrospinning to achieve porous structures. Shape fixation and recovery are achieved via the solvation and recrystallization of the hydrophilic PEG switching segment. Mechanical testing is performed to determine the SMP functionality. Water uptake rate for porous SMP is found to be higher than bulk SMP partly due to higher surface area for water contact. This enables porous structure water-responsive SMPs to recover faster compared to bulk SMPs. The water-responsive SMP exhibits good extents of shape fixity and shape recovery when immersed in water (≈35 °C). Different actuation times can be achieved based on the total surface area and efficiency of water-entry into the polymer. A porous and bulk water-responsive urethane-based shape memory polymer (SMP) is fabricated. Shape fixation and recovery are achieved via the solvation and recrystallization of hydrophilic poly(ethylene glycol) switching segment. Water-responsive SMP exhibits good extent of shape fixity and recovery immersed in water (≈35 °C). Different actuation times can be achieved based on the total surface area and efficiency of water-entry.



Cellulose Sponge with Superhydrophilicity and High Oleophobicity Both in Air and under Water for Efficient Oil–Water Emulsion Separation

2017-06-26T07:13:27.020214-05:00

Oil–water emulsions stabilized by surfactants are fine dispersions of oil in water or of water in oil and difficult to separate which will lead to serious water pollution. A more recent development is the ability to fabricate oleophobic–hydrophilic surfaces in air, which are not easy to construct due to the difference surface tension between water and oil. Herein, a cellulose sponge with multipore structure is fabricated to increase the removal efficiency. Amphiphilic molecular brushes of polyethylene glycol with short perfluorinated end caps (F-PEG) are grafted on cellulose sponges to solve the contradictory relation of hydrophilicity and oleophobicity and improve oil/water selective wettability and fouling resistance. Besides, stable superhydrophilicity and superoleophobicity under water, corrosive liquids, and high oleophobicity in air conditions are exhibited in the F-PEG grafted porous cellulose sponges with textured surfaces (F-g-CS). And the separation efficiency and rate of F-g-CS with surface of nanopores are 99.92% and 180 L m−2 h−1, while that of micropores are 99.83% and 297 L m−2 h−1 only under gravity. It is demonstrated that the grafting F-PEG molecules imparted F-g-CS of micropores surface with high flux and separation efficiency simultaneously. Furthermore, antifouling property and collection of water in oil–water mixture without fouling are possessed in F-g-CS. Amphiphilic molecular brushes are grafted on cellulose sponges to solve the contradictory relation of hydrophilicity and oleophobicity and improve oil/water selective wettability and fouling resistance. Besides, stable superhydrophilicity and high oleophobicity in air are exhibited in the modified porous cellulose sponges with textured surfaces.



Nanostructured Semiconducting Polymer Films with Enhanced Crystallinity and Reorientation of Crystalline Domains by Electrospray Deposition

2017-05-22T01:45:51.933859-05:00

Self-organization of conjugated polymer such as poly(3-hexylthiophene) (P3HT) causes directional anisotropy in the charge carrier mobility. In contrast to an edge-on orientation formed in thin films of P3HT made by spin coating, in this study electrospray deposition rotates the orientation while producing nanopillar structures as a result of Coulombic fission and significant evaporation of solvent from the droplets. The nanostructured films are investigated by scanning electron microscopy. Due to substantial polymer–air interfaces oriented perpendicular to the substrate, P3HT molecules adopt a face-on orientation with respect to the substrate plane that is confirmed by grazing incidence X-ray diffraction. Additionally, enhanced crystallinity (29% increase) is confirmed by a redshift in the UV–vis absorption spectra. Because deposition by electrospray is a scalable nanomanufacturing method, these results inform the design of low-cost device layers for large-surface-area applications such as light emitting diodes and photovoltaics. Electrospray deposition is used to rotate the orientation of polymer chain stacking in poly(3-hexylthiophene) (P3HT) and produce nanopillar structures. These nanostructured films are investigated by scanning electron microscopy and grazing incidence X-ray diffraction to reveal that the P3HT molecules adopt a face-on orientation with respect to the substrate plane. Furthermore, enhanced crystallinity (29% increase) is confirmed by UV–vis absorption.