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.
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.
Nanofiber production platforms commonly rely on volatile carrier solvents or high voltages. Production of nanofibers comprised of charged polymers or polymers requiring nonvolatile solvents thus typically requires customization of spinning setup and polymer dope. In severe cases, these challenges can hinder fiber formation entirely. Here, a versatile system is presented which addresses these challenges by employing centrifugal force to extrude polymer dope jet through an air gap, into a flowing precipitation bath. This voltage‐free approach ensures that nanofiber solidification occurs in liquid, minimizing surface tension instability that results in jet breakup and fiber defects. In addition, nanofibers of controlled size and morphology can be fabricated by tuning spinning parameters including air gap length, spinning speed, polymer concentration, and bath composition. To demonstrate the versatility of our platform, para‐aramid (e.g., Kevlar) and biopolymer (e.g., DNA, alginate) nanofibers are produced that cannot be readily produced using standard nanofiber production methods.
Carbon nanofiber/polycaprolactone (CNF/PCL) composite fibers are fabricated using a microfluidic approach. The fibers are made with different content levels of CNFs and flow rate ratios between the core and sheath fluids. The electrical conductivity and tensile properties of these fibers are then investigated. It is found that at a CNF concentration of 3 wt%, the electrical conductivity of the composite fiber significantly increases to 1.11 S m−1. The yield strength, Young's modulus, and ultimate strength of the 3 wt% CNF increase relative to the pure PCL by factors of 1.72, 2.88, and 1.23, respectively. Additionally, the results show that a microfluidic approach can be considered as an effective method to align CNFs along the fibers in the longitudinal direction.
Poly(3‐hydroxybutyrate), P3HB is a thermoplastic polyester synthesized from bacterial fermentation with potential uses in packaging due to its biodegradability. Nevertheless, P3HB is a fragile material and its processing temperature window is very narrow which restricts its use. This study explores the potential of vegetable oil‐derived plasticizers, i.e., maleinized linseed oil (MLO) and an epoxidized fatty acid ester (EFAE) in the 5–20 phr range as environmentally friendly solutions for P3HB industrial formulations with improved toughness. The results show that optimum balance between ductile properties is achieved with low plasticizer content (5 phr) for both plasticizer types. Elongation at break and the impact resistance are increased by 28 and 71% respectively after addition of 5 phr MLO. With regard to EFAE, the elongation at break is improved by 40% and the impact resistance is increased to twice the value of P3HB. Another effect that both plasticizers provide is the thermal stabilization with a delay in the onset degradation temperature.
3D aligned electrospun fibers hold a promising potential in a wide range of biomedical areas, including biosensors, controlled drug release, tissue engineering, etc. Thus, a cost‐effective and easy way to scale‐up fabrication for 3D aligned nanofibers is highly desired. Herein, a novel yet facile preparation process of 3D aligned nanofibers (3D AFs) by an improved electrospinning technique is reported. The obtained 3D AFs show enhanced controllability on morphology and fiber density, and thus facilitate adhesion and growth of human mesenchymal stem cells within their 3D nanofiber microarchitectures, leading to an excellent in vitro biocompatibility. Moreover, the 3D AFs with aligned morphology can enhance the neuron activities and induce directional cell growth along the direction of nanofiber orientation, thereby providing an excellent cue for the anchorage and migration dependent neurons. Combined with controllable morphology and structure, it is anticipated that this finding can lead to great applications of electrospun fibers in nerve tissue engineering, diagnostics, and other biomedical fields.
Polymerization shrinkage of dental composites remains a major concern. Free‐radically polymerizable cyclic monomers can be a conceivable alternative to methacrylates for the development of low‐shrinkage composites. In this study, the one‐step synthesis of the novel low viscosity difunctional vinylcyclopropanes 1 – 4 is described. Photopolymerization kinetics of these monomers are investigated by photo‐differential scanning calorimeter, using bis(4‐methoxybenzoyl)diethylgermane as photoinitiator. Real‐time near‐infrared photorheology measurements are performed to evaluate rheological behavior (i.e., time of gelation, polymerization‐induced shrinkage force) and chemical conversion (i.e., double bond conversion at the gel point, final double bond conversion) of the vinylcyclopropanes in situ. The potential of these monomers as reactive diluents in dental restorative materials is evaluated. Composites based on vinycyclopropanes 1 – 4 show good mechanical properties and exhibit significantly lower volumetric shrinkage and shrinkage stress than corresponding dimethacrylate‐based materials. The results indicate that such monomers are promising candidates for the replacement of commonly used low viscosity dimethacrylates such as triethylene glycol dimethacrylate in dental composites.
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.
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.
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.
Assembly of anisotropic nanoparticles on polymeric templates has attracted much attention recently because of the potential useful applications. In this work, 3D electrospun nanofiber membrane is used as template for the assembly of ex situ synthesized palladium nanocubes. The assembly process is achieved by simple immersion step, in which the electrostatic assembly of the nanocubes occurs. The dense nanocubes on the nanofibers as well as the fibrous nanostructure render the nanocomposite membrane excellent catalytic activity. Moreover, the catalytic membrane can be recycled for at least six times, which makes it possible for practical usage.
Electrospinning (e‐spinning) has been extensively explored as a simple, versatile, and cost‐effective method in preparing ultrathin fibers from a wide variety of materials. Electrospun (e‐spun) ultrathin fibers are now widely used in tissue scaffold, wound dressing, energy harvesting and storage, environment engineering, catalyst, and textile. However, compared with conventional fiber industry, one major challenge associated with e‐spinning technology is its production rate. Over the last decade, compared with conventional needle e‐spinning, needleless e‐spinning has emerged as the most efficient strategy for large‐scale production of ultrathin fibers. For example, rolling cylinder and stationary wire as spinnerets have been commercialized successfully for significantly improving throughput of e‐spun fibers. The significant advancements in needleless e‐spinning approaches, including spinneret structures, productivity, and fiber quality are reviewed. In addition, some striking examples of innovative device designs toward higher throughput, as well as available industrial‐scale equipment and commercial applications in the market are highlighted.
In spite of great concern on the wide application of silicone rubber foams, few works have been reported about easy‐operating foaming method. In this study, the effects of silica content and foaming process on the porous structure of high‐temperature‐vulcanized silicon rubber foams are evaluated, which are prepared by supercritical CO2 at different conditions, with fumed silica used for reinforcement. Silicone rubber foams with cell size in 8–120 μm, cell density in 105–108 cm−3, and density between 0.45 and 0.9 g cm−3 are prepared under different saturation conditions. The results show that increasing silica content can decrease cell size. It is also found that cell density improves exponentially with increasing saturation pressure and decreasing saturation temperature. Besides, it demands less than 1 h for specimens to reach equilibrium on thickness around 3 mm. All the results indicate that the porous structures of silicone foams can be tailored by foaming process parameters facilely and are predictable with fitted equation.
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.
Segmental polyurethanes (PU) with hydrophilic segments form colloidal dispersions which are ultimately arrested into gel‐like structure in aqueous continuous phase owing to the differential interactions between polymer and solvent. These structural states of amphiphilic PUs evolve hierarchically, but the structure‐function correlation between PU colloidal dispersion and gels is not clear. Here, this correlation is defined from the mechanomorphology of hydrophilic polyethylene glycol based PU which forms dispersions and finally transforms into gel‐structure. Morphological and rheological analyses show that PU with comparable hydrophilic and hydrophobic content forms attractive colloids with self‐similar fractal microstructures whereas PU with increased hydrophilic character forms space‐filling colloids without any defined organization. Furthermore, colloidal dispersions are densified under shear or gravity to form gel where gel mechanics is defined by colloidal particle organization and the morphology is dependent on gelation mode. This stepwise organization of PU colloidal particles into microgel can independently control microgel mechanics and morphology.
Biodegradable polyphosphazenes are important class of biomaterials. Their preparation typically requires specialized setup, inert conditions, and cumbersome and multiple processes. This work focuses on the synthesis of both nonfunctional and novel functional poly[(amino acid ester)phosphazene]s using a simplified thermal ring opening polymerization in air, followed by one‐pot ( 1P ) room temperature substitution, also in air. While some hydrolysis was inevitable under such conditions, purified materials with lower polydispersity indices than previously reported and acceptable yields were successfully and reproducibly obtained. The poly[(amino acid ester)phosphazene]s developed in this work are based on l ‐alanine, l ‐phenylalanine, and l ‐methionine with l ‐glutamic acid to render them functionality. Characterization of these synthesized materials demonstrated that the 1P substitution was successful in developing mono‐ and co‐substituted poly[(amino acid ester)phosphazene]s. Cytotoxicity studies on 2D films showed the materials to be compatible with NIH‐3T3 fibroblasts while confocal imaging of cells showed a well‐spread morphology with abundant F‐actin within the cytoskeleton. The l ‐phenylalanine‐based poly[(amino acid ester)phosphazene]s also showed significantly enhanced cell viability over tissue culture polystyrene at days 1 and 3 of cultivation (p < 0.01). Overall, this study has shown that poly[(amino acid ester)phosphazene]s can be obtained with acceptable yields and straightforward reaction conditions, leading to materials suitable for broader biomedical applications.
Polyaniline (PANI) has served as one of the most promising conducting materials in a variety of fields including sensors, actuators, and electrodes. Fabrication of 1D PANI fibers using electrospinning methods has gained a significant amount of attention. Due to the extremely poor solubility of PANI in common organic solvents, fabrication of electrospun PANI fiber has been carried out either by using corrosive solvents such as H2SO4 or by electrospinning in the presence of other matrix polymers. Herein, a new approach to the fabrication of PANI fibers using tert‐butyloxycarbonyl‐protected PANI (t‐Boc PANI) as the conducting polymer precursor is reported. The t‐Boc PANI is soluble in common organic solvents (e.g., chloroform and tetrahydrofuran), and electrospinning of t‐Boc PANI in those solvents affords nano/micrometer‐sized t‐Boc PANI fibers. Treatment of the electrospun t‐Boc PANI fibers with HCl results in the removal of the acid labile t‐Boc group and the generation of conducting (≈20 S cm?1) PANI fibers. The HCl‐doped PANI fibers are successfully used in the detection of gaseous ammonia with a detection limit of 10 ppm.
A facile method to fabricate ionic polymer‐metal composite (IPMC) actuators is proposed. A blend of mesoporous graphene (MG) and Nafion is used as the ionic matrix, which is sandwiched by two layers of blend of reduced graphene oxide (rGO) and Nafion as the electrodes. When subjected to an electrical field of 3 V, the IPMC actuator exhibits a blocking force of 10 gf g?1 for 20 s, and the same behavior can be repeatedly played for hundreds of cycles. MG improves the mechanical properties of Nafion‐based IPMC, more importantly, the mesopores in graphene provide additional pathway for the diffusion of cationic clusters and thus enhance the actuation speed. In addition, the surface electrodes of rGO protect the interlamellar liquid from evaporation thus ensure the durability.
Polymer‐based electrospun fibers have been intensively studied as antimicrobial membranes, drug carriers, and energetic materials. Inorganic fillers or small molecules have been routinely added into polymer matrices in order to enhance product functions. However, the electrospinning process is kinetically controlled and solvent rapidly evaporates due to the large surface‐to‐volume ratio of spinning liquid jet. When electrospinning a multicomponent system, complex phase behavior may occur and give rise to interesting internal structures of resulting products. Such kinetically driven phenomena deserve more attention for optimizing product performance. Here, electrospun poly(ε‐caprolactone)(PCL)/aminopropyl‐heptaisobutyl‐polyhedral oligomeric silsesquioxane (AMPOSS) fibers with AMPOSS content up to 30 wt% are studied as a model system to understand the impact of kinetically controlled phase separation on the fibers' internal structure, properties, and thermal stability. With sufficient AMPOSS loading, the hybrid fibers are found to have an AMPOSS‐shell/PCL‐core structure. The thermal stability of the as‐spun PCL/AMPOSS fibers is therefore greatly enhanced.
