Wongi Jang

PVdF/graphene oxide hybrid membranes via electrospinning for water treatment applications

Membrane materials based on poly (vinylidene fluoride) (PVdF) have received great attention recently due to their outstanding mechanical property and chemical resistance. However, this material can easily cause a membrane fouling problem due to its hydrophobic nature. This paper describes how to overcome this problematic issue by incorporating hydrophilic graphene oxide (GO) into PVdF-based membranes. Herein, PVdF nanofiber membranes loaded with GO were prepared via an electrospinning method and the hybrid membranes were characterized for water treatment applications. Graphene oxide sheets were initially prepared by the Hummers method. The pore property of the PVdF/GO hybrid nanofiber membrane for microfiltration (MF) applications was controlled by systematically increasing the number of nanofiber layers and thermal treatment. These resulting materials were characterized by SEM, FT-IR, UV-Vis, Raman spectroscopy, and tensometer. The overall results showed the reliable formation of the hybrid membranes which possessed controlled pore-diameters (∼0.2 micron) and narrow distribution. Based on contact angle tests, these PVdF/GO nanofiber hybrid membranes exhibited very hydrophilic characteristics. In addition, the hybrid membrane showed high pure water flux results up to 3 times and outstanding flux decline with 0.1 g L−1 Kaolin solutions compared to a neat PVdF nanofiber membrane. Based on all these results, it can be speculated that the incorporation of GO into PVdF could also improve the antifouling ability of the membrane system and will allow for their use as a water-treatment membrane.

A strategy to design biocompatible polymer particles possessing increased loading efficiency and controlled-release properties

Temperature-responsive poly(N-isopropylacrylamide), or poly(NIPAM), layers were reliably prepared around guest molecule (i.e., rhodamine B)-loaded mesoporous silica (SiO2) particles via thermally- and light-induced radical polymerizations. Subsequent removal of the sacrificial SiO2 particles with dilute hydrofluoric acid led to the formation of biocompatible polymer particles possessing a high dose of rhodamine B. The use of SiO2 core templates not only led to the formation of a uniform coating of the poly(NIPAM) layers, but also increased the stability of the guest molecule, rhodamine B, throughout polymerization. Interestingly, the light-induced radical polymerization method resulted in much less inevitable leaching and decomposition of azo-based guest molecules. The structural information and overall dye-loading efficiency of the mesoporous particles and the final polymer particles were then thoroughly examined by electron microscopes, dynamic light scattering, and fluorescence spectroscopy. As poly(NIPAM)-based particles exhibited significant swelling and deswelling properties above and below the lower critical solution temperature, the controlled-release properties of the poly(NIPAM) particles prepared by both methods were also evaluated. Generally, the dye-loaded poly(NIPAM) particles prepared by the light-induced approach resulted in a thinner coating of the polymer layers and exhibited much higher loading and tunable release profiles of the loaded guest molecules than those prepared by the thermally-induced polymerization. Given these features, the generalization of our strategy to design chemotherapeutically interesting drug-loaded polymer particles that are biocompatible and sensitive to external stimuli will allow for the further development of novel biomedical delivery and treatment systems.

Synthesis and Evaluation of PVA-CN Additive for High Thermal Stability of Lithium Secondary Battery Electrolyte

Currently liquid electrolyte having good ion-conductivity and high electrochemical stability has been used for the lithium secondary battery. But it has been reported there was a serious problem in the high temperature stability. In this study, the development of PVA-CN cyanoethyl polyvinyl alcohol additive which is used in lithium secondary battery electrolyte was carried out with two steps; the first step was the dissolution of PVA raw materials, and the second step was the synthesis of PVA-CN. The thermal property of the prepared PVA-CN was quantitatively analyzed using TGA. The significantly improved thermal stability of the electrolytes containing PVA-CN additives was also confirmed by monitoring swelling behavior of the membranes at high temperature, i.e. 29% less swelling effect, although they exhibited slightly lower ion conductivity, about 6% lower than commercially available electrolytes. This finding clearly suggests the possibility of preventing the swelling issue at high temperature which is the main cause of dangerous accidents from secondary battery systems.