3 research outputs found
Crystal Orientation Behavior and Shape-Memory Performance of Poly(vinylidene fluoride)/Acrylic Copolymer Blends
The crystal orientation behavior and shape-memory performance of miscible poly(vinylidene fluoride) (PVDF)/acrylic copolymer blends in various ratios have been investigated. With the incorporation of amorphous acrylic copolymer into the gallery of PVDF lamellae, the molecular connection (tie molecule concentration) between the neighboring PVDF crystals decreases gradually. For the blends with more than 80 wt % PVDF, most of the PVDF α-crystals are transformed into β-crystals upon deformation, and the molecular chains of the β-crystals are aligned along the stretching direction because tie molecules transfer the loading effectively. For the blends with less than 30 wt % PVDF, almost all of the PVDF crystals are isolated from each other with very few tie molecules. Mechanical deformation induces the perpendicular crystal molecular chain arrangement with no crystal form transitions. For the blends with 40 wt % to 70 wt % PVDF, the <i>c</i>-axis-oriented β-phase and the tilt-oriented α-phase coexist in the uniaxially stretched blends. The shape-memory properties of the blends were also evaluated over the same blend composition range. The maximum shape-memory recovery properties were observed for the blend sample containing 50 wt % PVDF, in which a small amount of tie molecules connect the PVDF crystallites to form a deformable elastic network. This network contributes to the good shape-memory properties of the blend. For the blends with very few tie molecules or high tie molecule concentrations, the deformation induces the slipping of the amorphous molecules or the large fibrillar crystal structure, respectively; thus, these samples exhibit relatively low shape-memory performance
Programmable Structure Control in Cigarlike TiO<sub>2</sub> Nanofibers and UV-Light Photocatalysis Performance of Resultant Fabrics
Novel
cigarlike nanofibers with an outer-shell and inner-continuous-pore
structure and resultant fabrics have been fabricated by coupling the
self-assembly of polystyrene-<i>block</i>-poly(ethylene
oxide) (PS-<i>b</i>-PEO) containing titanium precursors
with the electrospinning technique in our previous work [You et al. ACS Appl. Mater. Interfaces 2013, 5, 2278]. In the current work, the structure control in these nanofibers
has been investigated in detail using scanning electron microscopy,
focused ion beam, and small angle X-ray scattering. Our results indicate
that electrospinning conditions, the adopted solvent, the volume fraction
of PS-<i>b</i>-PEO block copolymer, and the amount of titanium
tetraisopropoxide in the mixture produce significant effects on both
outer-shell and inner-continuous structures in the nanofibers. The
parameters discussed above make it possible to achieve programmable
structure control in the aspect of the diameter, thickness of the
outer shell, and inner continuous pore. As a result, both micropores
among fibers and nanopores in certain fibers are under their control.
Furthermore, the photocatalytic activity of resultant TiO<sub>2</sub> fabrics was investigated by taking the photodegradation of Rhodamine
B as an example. The results suggest that the degradation efficiency
and rate constant exhibit sensitivity on the structure of nanofibers
Novel Cigarlike TiO<sub>2</sub> Nanofibers: Fabrication, Improved Mechanical, and Electrochemical Performances
By
coupling the self-assembly of polystyrene-block-poly(ethylene oxide)
(PS-b-PEO) containing titanium precursors with the electrospinning
technique, novel cigarlike nanofibers with an outer-shell and inner-continuous-pore
structure and resultant fabrics were fabricated. Different from typical
porous metal oxides, the prepared high-surface-area nonwoven fabrics
show excellent mechanical properties. Not only are these fabrics self-supporting
over a large area, but they can also be cut using scissors, which
is important for large-scale applications. Furthermore, as electrode
materials in Li-ion batteries, these fabrics exhibit much higher charge/discharge
capacity and cycle stability compared with the commercially available
nanosized TiO<sub>2</sub> (P25). The improved mechanical and electrochemical
performances are attributed to the presence of an outer-shell, inner-bicontinuous
structures (including continuous TiO<sub>2</sub> frame and continuous
nanopores) and hierarchical pores from the cigarlike nanofibers