Conductive textiles with exceptional electrical properties have been prepared by coating the conjugated polymer, poly(3,4‐ethylenedioxyphiophene)‐polystyrenesulfonate(PEDOT‐PSS), on polyethylene terephthalate (PET) nonwoven fabrics. Phase segregation from covalent bond formation to surface silica particles generates PEDOT‐PSS coated textiles that hold potential for wearable electronics due to the breathability of the fabric, low toxicity, easy processing and lightweight with high current carrying capacity. The conductive textiles were demonstrated for applications such as electrical connections and resistive heating.
Proton exchange membranes for fuel cell applications are synthesized by surface‐initiated (SI) atom transfer radical polymerization (ATRP). Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) is electrospun into 50 µm thick mat, which is then employed as multifunctional initiator for copper‐mediated SI ATRP of 4‐styrene sulfonic acid sodium salt. Fine‐tuning of the ATRP conditions allows adjustment of the membrane's ion exchange capacity by varying the loading of the grafted ionomer. Structure and composition of the membranes are investigated by spectroscopic means and thermogravimetric analysis, respectively. The membrane morphology is probed by scanning electron microscopy. A membrane with proton conductivity as high as 100 mS cm−1 is obtained. Long‐term durability study in direct methanol fuel cells is conducted for over 1500 h demonstrating the viability of this novel facile approach.
Visible light curing of photopolymers has gained increasing interest in recent years. Dental materials are one of the important areas of application, where the bimolecular camphorquinone/amine initiator system is currently state of the art initiator. In this study, the authors describe the synthesis and photochemistry of tetrakis(2,4,6‐trimethylbenzoyl)silane, as cleavable Type I visible light photoinitiator. Besides excellent photobleaching behavior, this photoinitiator can well compete with up to now used long wavelength initiators.
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.
Photo‐reversible polyurethane (PU) coatings based on coumarin diol (CD) are obtained. Initially, pre‐polymers based on different amounts of coumarin (5, 15, and 25 mol%) and 1,6‐hexamethylene diisocyanate are prepared to obtain PUs with a large incorporation of CD and high molecular weight. The pre‐polymer is posterior reacted with poly(ε‐caprolactone) diol (PCL‐diol), either with molecular weight = 530 or 2000 g mol–1. The thermal stabilities of the PUs are studied using thermogravimetric analysis. Polymers with a higher content of CD present higher stability. The thermal transitions and the mechanical response are analyzed using differential scanning calorimetry and strain‐stress tests, respectively. Moreover, the photo‐reversibility of CD‐based PUs is followed by UV absorption. In general, photo‐dimerization induces better mechanical properties of the final PUs. Materials obtained with short PCL‐diol ( = 530 g mol–1) and the highest amount of CD present higher reversibility processes. Therefore, these polymers are promising for application as coating systems.
The assembly of natural and synthetic polymers into fibrous nanomaterials has applications ranging from textiles, tissue engineering, photonics, and catalysis. However, rapid manufacturing of these materials is challenging, as the state of the art in nanofiber assembly remains limited by factors such as solution polarity, production rate, applied electric fields, or temperature. Here, the design and development of a rapid nanofiber manufacturing system termed pull spinning is described. Pull spinning is compact and portable, consisting of a high‐speed rotating bristle that dips into a polymer or protein reservoir and pulls a droplet from solution into a nanofiber. When multiple layers of nanofibers are collected, they form a nonwoven network whose composition, orientation, and function can be adapted to multiple applications. The capability of pull spinning to function as a rapid, point‐of‐use fiber manufacturing platform is demonstrated for both muscle tissue engineering and textile design.
Green synthesis is one of the hot topics in the chemistry of hybrid organic–inorganic materials. A alcohol‐free sol–gel process has been developed to prepare optically transparent hybrid films from an epoxy bearing alkoxide, [2‐(3,4‐epoxy‐cyclohexyl)‐ethyl]‐trimethoxysilane (ECTMS). The synthesis is simple and effective because only two components, ECTMS and an aqueous solution of NaOH, are employed. Infrared spectroscopy has been used to monitor the reactivity of the precursor sol as a function of the aging time. Organic–inorganic hybrid films have been then prepared with the different sols via spin‐coating. The presence of the cyclohexyl ring slows down dramatically both the epoxide opening and the capability of the resulting diols in forming a tricyclic dioxane derivative. The highly basic conditions employed in the synthesis favor the formation of the cyclohexyl rings and cage‐ and ladder‐like silica structures. The hybrid films have shown a high transmittance in the visible range and a thermal stability up to 200 °C.
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.
The role of mechanical constraint on the tearing behavior of perfluorosulfonic acid and polyethylene membranes is examined. A constrained tearing test is employed to measure the tearing energy when the formation of a plastic zone ahead of the tear tip is constrained. It is shown that the tearing energy decreases with increasing constraint associated with a smaller plastic zone and is much lower than the tearing energy with no constraint. Furthermore, it is demonstrated that the tearing rate has a strong effect on the tearing energy when the membrane is unconstrained, but a much smaller effect when the membrane is constrained as the viscoelastic relaxation processes related to the plastic zone are suppressed. The results highlight the significant role of mechanical constraint on the tearing behavior of membranes during both testing and in application.
Development of artificial soft materials that have good mechanical performances and autonomous healing ability is a longstanding pursuit but remains challenging. This work reports a kind of highly flexible, tough, and self‐healable poly(acrylic acid)/Fe(III) (PAA/Fe(III)) hydrogels. The hydrogels are dually cross‐linked by triblock copolymer micelles and ionic interaction between Fe(III) and carboxyl groups. Due to the coexistence of these two cross‐linking points, the resulting PAA/Fe(III) hydrogels are tough and can be flexibly stretched, bent, knotted, and twisted. The hydrogels can withstand a deformation of 600% and an ultimate stress as high as 250 kPa. Moreover, the dynamic ionic interaction also endows the hydrogels self‐healing properties. By varying the ratio of Fe(III)/AA, a compromised healing efficiency of 73% and an ultimate stress of 200 kPa are obtained.
The direct injection of a drug into a joint can relieve osteoarthritic pain for a short period of time. The problem is that the drug will not stay at the allocated location. Therefore, a proof‐of‐concept in situ is designed forming hydrogel containing liposomes that are covalently linked to the hydrogel network. When the liposomes are filled with a cargo, the formed hydrogel is thus loaded with this cargo, too. Due to the link between the hydrogel and the liposomes, a compression or other mechanical force applied to the hydrogel will rupture the liposomes and release a small percentage of the cargo. Overall, a long‐term intra‐articular drug release is feasible.
A fundamental study on the sterilization of thiol‐ene/acrylate polymers for biomedical applications is presented. These polymer networks belong to the emerging field of shape memory polymers and have the capability to undergo softening after insertion into the body. The impact of various sterilization methods, such as radiation, steam, and ethylene oxide on the thermomechanical properties of these stimuli responsive materials is investigated. Time and temperature dependent thermomechanical properties of sterilized and nonsterilized samples are determined by means of dynamic mechanical analysis in an aqueous environment to allow testing of polymers in phosphate buffered saline. The findings show that ethylene oxide sterilization is appropriate for thiol‐ene and thiol‐ene/acrylate based shape memory polymers. This method does not adversely affect thermomechanical and self‐softening properties and after sterilization, endotoxin levels remain below the thresholds recommended in the FDA Guidance.
For major advances in microfabricated drug delivery systems (DDS), fabrication methods with high throughput using biocompatible polymers are required. Once these DDS are fabricated, loading of drug poses a significant challenge. Here, hot punching is presented as an innovative method for drug loading in microfabricated DDS. The microfabricated DDS are microcontainers fabricated in photoresist SU‐8 and biopolymer poly‐l ‐lactic‐acid (PLLA). Furosemide (F) drug is embedded in poly‐ε‐caprolactone (PCL) polymer matrix. This F‐PCL drug polymer matrix is loaded in SU‐8 and PLLA microcontainers using hot punching with >99% yield. Thus, it is illustrated that hot punching allows high‐throughput, parallel loading of 3D polymer microcontainers with drug‐polymer matrices in a single process step.
Adsorption of a typical example of a new class of amino cellulose, namely 6‐deoxy‐6‐(2‐aminoethyl)amino cellulose at different pH‐values and in the presence of electrolytes, onto cellulose model substrates is studied with surface plasmon resonance and quartz crystal microbalance with dissipation monitoring. Unexpectedly, adsorption is consistently higher at a higher pH‐value of 10, indicating that solubility and interactions between amine moieties and cellulose are more important than electrostatic interactions. The findings are highly relevant for the process to modify material surfaces with amino cellulose in water‐based systems as a universal tool for changing the surface properties and chemistry. Potential applications for an antimicrobial all biobased material could be found, e.g., as medical textiles or in the biotechnology sector.
Curdlan (β‐1,3 glucan) (7 wt%) with polyvinyl alcohol (PVA) (10 wt%) is blended at 1:2 weight ratio and electrospun to get nanofibers and is crosslinked with glutaraldehyde vapor to make it insoluble in water. It has a fiber diameter of less than 100 nm and is hydrophilic (contact angle = 35°). It is biodegradable (10% in 14 d) and also has a good swelling behavior (≈170%). More than 100% of L6 cells are viable on this scaffold after 3 d. The scanning electron microscope images also reveal that cells are able to attach and spread in the nanofibrous scaffolds. In vitro scratch assay indicates that the wound closure rate of curdlan/PVA scaffold is better than PVA scaffold probably due to the immunomodulatory properties of the biopolymer. Thus our results indicate that curdlan/PVA scaffold can be an ideal material for wound healing applications.
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.
Supramolecular nanofibers have a great potential to be used as gelating agents, polymer additives, and fibrous material for filtration purposes. To meet the requirements for practical and industrial applications on a large scale, e.g., production of filter media, it is desirable to develop supramolecular systems processable from environmentally friendly water‐based solvent mixtures. Moreover, assessing processing parameters to control the micro‐ and nanofiber diameter is of vital importance. Therefore, an alkoxy‐substituted 1,3,5‐benzenetrisamide, N,N′,N″‐tris(1‐(methoxymethyl)propyl)benzene‐1,3,5‐tricarboxamide is designed that can be self‐assembled into supramolecular nanofibers upon cooling from a water/isopropanol solvent mixture. It is demonstrated that parameters such as stirring velocity and the temperature range during processing allow for a precise adjustment of the cooling profile which in turn enables the control of the supramolecular nanofiber diameters.
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.
The construction of high‐quality 3D polymeric photonic crystal (PC) films featuring fascinating tunable optical properties in a facile and time‐efficient way remains a major concern. Herein, the rapid assembly of highly crystallized brilliant flexible 3D polymeric PC films and their application for multiresponsive colorimetric sensing are demonstrated. Monochromatic PC films with remarkably distinct structural color, narrow half‐band width (27 nm), and broad tunability of band‐gaps (from blue to red) are generated within seconds from highly concentrated and charged colloids (51 vol%, ?57.6 mV) embedded in poly(N‐isopropylacrylamide) matrix. A repulsion‐induced precipitation assembly is found to be responsible for the ultrafast formation of close‐packed PC colloidal arrays. Besides, the resultant PC films exhibit ultrasensitive and fast response to external stimuli, revealed by interesting droplet diffusion experiments. Thus these PC films can serve as efficient colorimetric sensing materials to visually determine diverse species including trace ionic strength (2.9 ppm), minor surfactant (1 × 10?3m ), alcohol, and pH variation (1.0–13.9).
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.
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