In-Situ Synchrotron SAXS and WAXS Investigation on the Deformation of Single and Coaxial Electrospun P(VDF-TrFE)-Based Nanofibers

Coaxial core/shell electrospun nanofibers consisting of ferroelectric P(VDF-TrFE) and relaxor ferroelectric P(VDF-TrFE-CTFE) are tailor-made with hierarchical structures to modulate their mechanical properties with respect to their constituents. Compared with two single and the other coaxial membranes prepared in the research, the core/shell-TrFE/CTFE membrane shows a more prominent mechanical anisotropy between revolving direction (RD) and cross direction (CD) associated with improved resistance to tensile stress for the crystallite phase stability and good strength-ductility balance. This is due to the better degree of core/shell-TrFE-CTFE nanofiber alignment and the crystalline/amorphous ratio. The coupling between terpolymer P(VDF-TrFE-CTFE) and copolymer P(VDF-TrFE) is responsible for phase stabilization, comparing the core/shell-TrFE/CTFE with the pristine terpolymer. Moreover, an impressive collective deformation mechanism of a two-length scale in the core/shell composite structure is found. We apply in-situ synchrotron X-ray to resolve the two-length scale simultaneously by using the small-angle X-ray scattering to characterize the nanofibers and the wide-angle X-ray diffraction to identify the phase transformations. Our findings may serve as guidelines for the fabrication of the electrospun nanofibers used as membranes-based electroactive polymers.

Gelation-Assisted Layer-by-Layer Deposition of High Performance Nanocomposites

Layer-by-layer (LBL) assembly produces nanocomposites with distinctively high volume fractions of nanomaterials and nanometer scale controlled uniformity. Although deposition of one nanometer scale layer at a time leads to high performance composites, this deposition mode is also associated with the slow multilayer build-up. Exponential LBL, spin coating, turbo-LBL and other methods tremendously accelerate the multilayer build-up but often yield lower, strength, toughness, conductivity, etc. Here, we introduce gelation assisted layer-by-layer (gaLBL) deposition taking advantage of a repeating cycle of hydrogel formation and subsequent polymer infiltration demonstrated using aramid nanofiber (ANF) and epoxy resin (EPX) as deposition partners. Utilization of ANF gels increases the thickness of each deposited layer from 1–10 nm to 30–300 nm while retaining fine control of thickness in each layer, high volume fraction, and uniformity. While increasing the speed of the deposition, the high density of interfaces associated with nanofiber gels helps retain high mechanical properties. The ANF/EPX multilayer composites revealed a rare combination of properties that was unavailable in traditional aramid-based and other composites, namely, high ultimate strength of 505±47 MPa, high toughness of 50.1±9.8 MJ/m3, and high transparency. Interestingly, the composite also displayed close-to-zero thermal expansion. The constellation of these materials properties is unique both for quasi-anisotropic composites and unidirectional materials with nanofiber alignment. gaLBL demonstrates the capability to resolve the fundamental challenge between high-performance and scalability. The gelation-assisted layered deposition can be extended to other functional components including nanoparticle gels.

Preparation of oriented bacterial cellulose nanofibers by flowing medium-assisted biosynthesis and influence of flowing velocity

Nanofiber alignment in tissue engineering scaffolds is a crucial factor controlling the cell behavior. In this work, we report a facile approach to obtain aligned nanofibers of bacterial cellulose (BC) by forcing the culture medium of bacteria to flow along a fixed direction. The emphasis of this work was placed on the effect of flowing velocity on the alignment of the as-prepared oriented BC (OBC). X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses indicated that the velocity affected the crystallinity and thermal stability of BC while the chemical structure did not change with the velocity. The controllable alignment of BC nanofibers makes them a promising material for the construction of biomimetic scaffolds for tissue engineering and regenerative medicine.