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Lecture on "Crystallization induced phase separation and structural relaxations in PVDF/PMMA (Polyvinylidene fluoride/ poly methyl methacrylate) blends in presence of multiwalled carbon nanotubes" - 28 October 2016

Date and Venue Information:
28 October 2016

Title of Lecture:
"Crystallization induced phase separation and structural relaxations in PVDF/PMMA (Polyvinylidene fluoride/ poly methyl methacrylate) blends in presence of multiwalled carbon nanotubes" by  Maya Sharma, Centre for Nano Science and Engineering (CeNSE), Indian Institute of Science, Bangalore

Abstract

PVDF/PMMA blend is a well-known UCST (upper critical solution temperature) system which forms a miscible phase at higher temperature but phase separates upon cooling, either by liquid-liquid phase separation (LLPS) or by solid-liquid separation through crystallization of PVDF. The blending of PVDF with PMMA (≤ 40% concentration) leads to phase separation mainly driven by fast crystallization of PVDF and formation of three distinct regions: PVDF crystallites, crystalline amorphous interphase and liquid-like amorphous regions. During crystallization, the PMMA phase occupies the interlamellar and interspherulitic regions of PVDF and there exists a clear boundary between ordered crystalline region and liquid-like amorphous region. In this work, the structural properties, the crystalline morphologies of various PVDF/PMMA blendwas studied by polarized optical microscopy (POM), rheology, FTIR and wide angle X-ray diffraction (WXRD) in presence and absence of MWNTs. The phase separated morphologies and the positioning of MWNTs in the blends was evaluated using SEM. The selective localization of MWNTs was investigated using selective dissolution technique.Further, different PVDF/PMMA (wt/wt) blends with and without MWNTs were chosen to investigate the segmental relaxations, fragility and the cooperativity near the Tg using differential scanning calorimetry (DSC) and broadband dielectric relaxation spectroscopy (DRS). The effect of MWNTs on the molecular mobility and structural relaxation is also discussed. MWNTs act as heteronucleating agent, and specifically interact with PVDF thereby influences the dynamics of PVDF chains. MWNTs can also restrict the amorphous segmental mobility and can influence the intermolecular cooperativity and coupling. Hence, the fragility, cooperativity and the intermolecular coupling can significantly alter in presence of high aspect ratio materials like MWNTs.The crystallization induced phase separation in various blends can result in various crystalline morphologies depending on the PVDF concentration. Hence, by selectively etching the amorphous phase (here PMMA), nanoporous morphology can be designed. As PMMA resides in the interlamellar and/or interspherulitic regions of PVDF, depending on its composition in the blends, porous structures of various length scales can be obtained. For instance, higher concentration of PMMA in the blend showed higher pore size as compared to lower concentrations. In view of this, the pure water flux can be tailored across different membranes.With suitable rendering of antibacterial surface, these membranes open new avenues in the existing membrane industry.