Mechanochemical transduction enables an extraordinary range of physiological processes such as the sense of touch, hearing, balance, muscle contraction, and the growth and remodelling of tissue and bone. Although biology is replete with materials systems that actively and functionally respond to mechanical stimuli, the default mechanochemical reaction of bulk polymers to large external stress is the unselective scission of covalent bonds, resulting in damage or failure. An alternative to this degradation process is the rational molecular design of synthetic materials such that mechanical stress favourably alters material properties. A few mechanosensitive polymers with this property have been developed; but their active response is mediated through non-covalent processes, which may limit the extent to which properties can be modified and the long-term stability in structural materials. Previously, we have shown with dissolved polymer strands incorporating mechanically sensitive chemical groups-so-called mechanophores-that the directional nature of mechanical forces can selectively break and re-form covalent bonds. We now demonstrate that such force-induced covalent-bond activation can also be realized with mechanophore-linked elastomeric and glassy polymers, by using a mechanophore that changes colour as it undergoes a reversible electrocyclic ring-opening reaction under tensile stress and thus allows us to directly and locally visualize the mechanochemical reaction. We find that pronounced changes in colour and fluorescence emerge with the accumulation of plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the ring-opening reaction is an activated process. We anticipate that force activation of covalent bonds can serve as a general strategy for the development of new mechanophore building blocks that impart polymeric materials with desirable functionalities ranging from damage sensing to fully regenerative self-healing.

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II. METHODS The continuum activation model developed herein relies on two smaller scale simulation methods (molecular a)

Composites made of silicon nanostructures in carbon matrixes are promising materials for anodes in Li ion batteries given the synergistic storage capacity of silicon combined with the chemical stability and electrical conductivity of carbonaceous materials. This work presents the development of Si/C composite fine fiber mats produced by carbonization of poly(vinyl alcohol) (PVA)/Si composites. PVA has a high carbon content (ca. 54.5%) and, being water-soluble, it promotes the development of environmentally friendly materials. Si nanoparticles were dispersed in PVA solutions and transformed into fine fibers using a centrifugal spinning technique given its potential for large scale production. The Si/PVA fibers mats were then subjected to dehydration by exposing them to sulfuric acid vapor. The dehydration improved the thermal and chemical stability of the PVA matrix, allowing further carbonization at 800 °C. The resulting Si/C composite fibers produced binder-free anodes for lithium ion batteries that delivered specific discharge and charge capacities of 952 mA h g and 862 mA g, respectively, with a Columbic efficiency of 99% after 50 cycles.

This study presents the thermo-physical, electrical, and mechanical characterization of fine carbon fibers produced from water-soluble polymer precursors and low temperature processes. These fibers were developed utilizing the Forcespinning® technology which utilizes centrifugal force to spin fibers. Polyvinyl alcohol was used as the precursor material, and fibers were developed and deposited in a non-woven configuration. The resultant nonwoven fiber mats were subjected to a dehydration process through exposure to sulfuric acid vapors. The partially carbonized mats were heat treated at 850 °C. The produced porous nonwoven carbon fiber based mats have micro-and mesoporosity with a final fiber average diameter of 191 nm. The electrical volume resistivity of the polymeric nanofibers was 8×10 14 Ω•cm and it dropped to 165 Ω•cm for the chemically treated carbon fiber mat and to 0.407 Ω•cm for the subsequently heat treated fibers. The electromagnetic (EMI) shielding effectiveness (SE) was observed to be 20 and 40 dB for the chemically treated fibers and heat treated fibers respectively. The tensile stress for the chemically treated fibers was 43 MPa with a strain of 18% while the subsequently heat-treated fibers exhibited a stress of 124 MPa and strain of 21%.

In the usual forcespinning (FS) process, a meso-scale fluid jet is forced through an orifice of a rotating spinneret, where the ambient fluid is air. This leads to the formation of a jet with a curved centerline. In this study we make use of a phenomenological viscosity model, which, in particular, takes into account both extension thinning and thickening of the polymeric jet, to investigate the properties of polymeric fiber jets during FS process. We consider the governing modeling systems for such rotating jets and calculate numerically the expressions for the nonlinear steady solutions for the jet quantities such as radius, speed, stretching rate, strain rate and trajectory versus arc length. We determine these quantities for different values of the parameters that represent effects due to rotation, viscosity and relaxation times for shear and extension. We also carry out experimental investigation for several types of polymeric fluid jets during FS process that provide general agreement with the present theoretical results.

Fine polyacrylonitrile (PAN) fibers were produced through a scalable centrifugal spinning process. Sodium chloride (NaCl) was added to the PAN‐dimethylformamide solution to decrease the surface tension and consequently promote a decrease in fiber diameter while increasing the fiber output. The fiber preparation process involved the centrifugal spinning of the PAN‐based solution; developed fibers were stabilized in air at 240°C followed by carbonization at 800°C under a Nitrogen atmosphere. The addition of sodium chloride to the PAN solution led to a 37% decrease in the carbon fiber diameter. The carbon fibers were analyzed by scanning electron microcopy, transmission electron microscopy (TEM), X‐ray diffraction, X‐ray photoelectron spectroscopy (XPS) and electrochemical experiments. The TEM results revealed improved graphitization with the addition of sodium chloride. The XPS analysis showed increased functionality (e.g. O2) on the surface of carbon fibers obtained from PAN/NaCl precursor fibers. A significant improvement was achieved in the electrochemical performance of carbon fibers made from PAN/NaCl precursor fibers compared to those made from pure PAN precursor fibers. POLYM. ENG. SCI., 58:2047–2054, 2018. © 2018 Society of Plastics Engineers

We report a scalable method to obtain a new material where large graphene sheets form webs linking carbon fibers. Film-fiber hybrid nonwoven mats are formed during fiber processing and converted to carbon structures after a simple thermal treatment. This contrasts with multistep methods that attempt to mix previously prepared graphene and fibers, or require complicated and costly processes for deposition of graphene over carbon fibers. The developed graphene-fiber hybrid structures have seamless connections between graphene and fibers, and in fact the graphene "veils" extend directly from one fiber into another forming a continuous surface. The graphene-fiber hybrid structures are produced in situ from aqueous poly(vinyl alcohol) solutions. The solutions were subjected to centrifugal spinning to produce fine nanofiber mats. The addition of salt to the polymer solution stimulated a capillarity effect that promoted the formation of thin veils, which become graphene sheets upon dehydration by sulfuric acid vapor followed by carbonization (at relatively low temperatures, below 800 °C). These veils extend over several micrometers within the pores of the fiber network, and consist of crystalline graphene layers that cross-link the fibers to form a highly interconnected hybrid network. The surface area and pore diameter of the hybrid structures were measured to be 521 mg and 10 nm, respectively. The resulting structure shows high electrical conductivity, 550 S/m, and promising shielding of electromagnetic interference, making it an attractive system for a broad range of electronic applications.