By coupling the self-assembly of polystyrene-block-poly(ethylene oxide)-containing titanium-tetraisopropoxide and tungsten hexaphenoxide (the precursors of TiO2 and WO3, respectively) with electrospinning technique, the hierarchically porous TiO2/WO3 composite nanofibers with inner-bicontinuous and outer-shell structures have been synthesized. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were employed to characterize the structure of the fibers. In these nanofibers, the TiO2 acts as the frames, and WO3 fills the gaps. The UV–vis spectroscopy suggests that the spectral response range has been successfully extended into the visible regime. Furthermore, the resulting fabrics show enhanced performance in the photocatalytic degradation of acetaldehyde relative to neat TiO2 and neat WO3. Our results indicate that electrospinning the blend solution of block copolymer and two kinds of precursor of inorganic material is an effective strategy to fabricate composite nanofibers that can improve the photocatalytic activity of TiO2, especially for visible light.

An effective strategy to tailor the microporous structures has been developed based on the shape memory effect in porous poly(l-lactic acid) membranes in which tiny crystals and amorphous matrix play the roles of shape-fixed phase and reversible-phase, respectively. Our results indicate that not only PLLA membranes but micropores exhibit shape memory properties. The proportional deformations on two scales have been achieved by uniaxial or biaxial tension, providing a facile way to manipulate continuously the size and the orientation degree of pores on microscale. The enhanced separation performance has been validated by taking polystyrene colloids with varying diameters as an example.Keywords: deformation; pore size; porous membranes; separation; shape memory effect;

The stability of bilayer polymer films upon solvent annealing has been investigated with the help of atomic force microscopy (AFM) by taking PMMA [poly(methyl methacrylate), the upper layer] and SAN [poly(styrene-ran-acrylonitrile), the bottom layer] system as an example. Our results indicate that the stability and structure evolution depend crucially on the selectivity of the adopted annealing solvents. In the vapor of acetic acid (HAc, the selective solvent for PMMA), the upper PMMA layer dewets on the stable bottom SAN layer; upon annealing in 1, 2-dichlorobenzene (OBD, the selective solvent for SAN) vapor, the bilayer film remains stable because it is very hard for OBD molecules to penetrate and cross the upper PMMA layer. When dimethylformamide (exhibiting much higher solubility for SAN than PMMA) is used to anneal the specimen, the solvent molecules swell and cross the upper PMMA layer and enrich in the bottom SAN layer. As a result, SAN layer dewets the substrate, producing some SAN droplets while the upper PMMA is “carried” by the movement of SAN. This is the reason for the rupture of the upper film and the formation of “SAN droplets covered by PMMA islands.”

•The parallel-stripe structures were fabricated in polymer blend by precise control of film thickness and resultant stability.•It is the lamellae twisting model that dominates the formation of parallel-stripe structures in PLLA/POM blend films.•The composition and isothermal crystallization temperature dependences were clarified based on the parallel stripes.Poly(l-lactic acid)/poly(oxymethylene) bulky blend is a typical system exhibiting ring-banded spherulites. In this work, however, the parallel ridges and valleys were fabricated for the first time in the blend film by the precise control of film thickness. They are named as “parallel-stripe structures” to distinguish from general “ring-banded structures”. Our results indicate that the cracks on thinner films prevent the development of ridge/valley rings along the film, accounting for the formation of these parallel structures. Consequently, they can reduce the influence of the fractal and resultant branching lamellae which makes the investigation of ring-banded structures more complicated. On the other hand, a novel in-situ etching method has been established to investigate the composition distribution of PLLA and POM in film thickness direction. As a result, the tri-layer structures including top-PLLA layer, blend layer and bottom-POM layer were reconstructed and validated by melting contact angles. Based on the atomic force microscope and transmission electron microscope results, it is concluded that the twisting model dominates the formation of parallel banded structures in PLLA/POM blend film. Furthermore, the crystallization temperature and composition dependence of lamellae twisting has been investigated in detail. On one hand, the increase of crystallization temperature leads to the well-developed POM crystal lamellae, which is the reason for the slower twisting. On the other hand, blend films with higher PLLA weight fraction produce bigger period and smaller radius during POM lamellae twisting because of the depression of the top PLLA wetting layer.Download high-res image (304KB)Download full-size image

The critical fluctuation intensity for the occurrence of dewetting, the basic and key problem in dewetting by means of composition fluctuation, remains obscure. In this work, therefore, the stability and fluctuation intensity of polymer films upon blending a tiny amount of a miscible component was investigated by taking poly(methyl methacrylate)/poly(styrene-ran-acrylonitrile) (i.e. PMMA/SAN) as an example. Our results indicate that both neat PMMA and neat SAN films wet the substrate of silicon oxide thermodynamically. SAN (with 1% or 2% PMMA) films dewet this substrate completely, while PMMA (with tiny amount of SAN) films are stable upon annealing at 145 °C. The fit and extrapolation of the RMSroughness suggest that the composition fluctuation and consequent surface undulation intensity accounts for the difference in film stability. The higher magnitude of fluctuation intensity results in the dewetting of the SAN film. On the other hand, the stronger interaction between PMMA and silicon oxide depresses the fluctuation and surface undulation along the film, which is the reason for the stable PMMA film.