A series of poly(vinylidene fluoride) (PVDF)/poly(vinyl alcohol) (PVA) composite films with different ratios were prepared by electrospinning. Because of the intermolecular interaction force, the highest thermal conductivity of the above film is 2.434 W m–1 K–1, which is about 60% higher than that of the pure PVDF film without a strong intermolecular interaction force. Infrared and wide-angle X-ray diffraction (WXAD) proved that PVDF as a thermal bridge enhances the internal interaction force and makes the internal structure more regular. The laser method shows that the film with strong intermolecular interaction has higher thermal diffusivity. Using molecular dynamics to explore the thermal expansion rate of the system, it is found that the intermolecular interaction force and the thermal bridge can effectively inhibit the activity of the molecular chain and reduce its free volume. After an in-depth study of the influence of the intermolecular interaction force and the thermal bridge on polymers, it is found that electrospinning can conveniently and effectively improve the ordering of the polymer structure. Integration of the electrospinning method and intermolecular interaction leads to the remarkable improvement of intrinsic thermal conductivity for polymer blends.
Ningen Hu,Tonghu Xiao,Xinhai Cai,Lining Ding,Yuhua Fu,Xing Yang
In this study, a nonsolvent thermally-induced phase separation (NTIPS) method was first proposed to fabricate hydrophilically-modified poly(vinylidene fluoride) (PVDF) membranes to overcome the drawbacks of conventional thermally-induced phase separation (TIPS) and nonsolvent-induced phase separation (NIPS) methods. Hydrophilically-modified PVDF membranes were successfully prepared by blending in hydrophilic polymer polyvinyl alcohol (PVA) at 140 °C. A series of PVDF/PVA blend membranes was prepared at different total polymer concentrations and blend ratios. The morphological analysis via SEM indicated that the formation mechanism of these hydrophilically-modified membranes was a combined NIPS and TIPS process. As the total polymer concentration increased, the tensile strength of the membranes increased; meanwhile, the membrane pore size, porosity and water flux decreased. With the PVDF/PVA blend ratio increased from 10:0 to 8:2, the membrane pore size and water flux increased. The dynamic water contact angle of these membranes showed that the hydrophilic properties of PVDF/PVA blend membranes were prominently improved. The higher hydrophilicity of the membranes resulted in reduced membrane resistance and, hence, higher permeability. The total resistanceRtof the modified PVDF membranes decreased significantly as the hydrophilicity increased. The irreversible fouling related to pore blocking and adsorption fouling onto the membrane surface was minimal, indicating good antifouling properties.Keywords:nonsolvent thermally-induced phase separation (NTIPS);PVDF/PVA blend membrane;hydrophilic modification;membrane resistance;antifouling property
Jiawei Cheng,Peizhi Wang,Xinyang Zhou,Zhilin Zhang,Jinxin Yao,Jiachen Xie,Yongchen Zong,Jun Ma,Wei Wang
The lack of robust distillation membranes to resist scaling/wetting remains a significant barrier to applying membrane distillation (MD) for hypersaline wastewater treatment. Constructing a functional surface layer was demonstrated to be a promising strategy against membrane scaling/wetting. However, conventional surface coating processes could increase water transport resistance and low compatibility between the surface layer and hydrophobic substrate, deteriorating membrane efficacies and stabilities. Herein, we successfully developed a surfactant-tailored PVDF/PVA composite membrane (SPCM) with a robust embedded interlocking structure. SPCM not only exhibited outstanding mechanical stabilities and anti-scaling/wetting capabilities during hypersaline wastewater treatment but also showed marvelous water permeability (exceeding the intrinsic permeability of hydrophobic substrate, ∼17%). We systematically investigated the effect of surfactant integration on the microstructural evolution and operational efficacies of functional surface layers. Detailed mechanisms of water transport enhancement were revealed by instrument characterization and experimental design. The embedded structure of surface layer, which decreased the water transfer distance and enhanced the evaporation area at the gel-layer/hydrophobic-substrate interface, was demonstrated to be the key to water flux enhancement. Besides, the post-treatment could further optimize the chemical structure of hydrogel networks and increase the proportion of intermediate water (IW) at the evaporation interface, facilitating water evaporation. SPCM also demonstrates outstanding efficiency and stability in the long-term cycle concentration of desulfurization wastewater. The high mechanical stability and exceptional operational efficiency of the SPCM, combined with the simplified membrane preparation process, endowed the SPCM with tremendous application potential for hypersaline water treatment.
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