Supercritical Gel Drying: A Powerful Tool for Tailoring Symmetric Porous PVDF−HFP Membranes

Abstract

In this work, poly(vinylidene fluoride) copolymer with hexafluoropropylene (PVDF-HFP) membrane-like aerogels have been generated for the first time. PVDF-HFP gels have been prepared from polymer-acetone solutions by adding various amounts of ethanol. A series of supercritical drying experiments have been performed at different pressures (from 100 to 200 bar) and temperatures (from 35 to 45 degrees C) and at various polymer concentrations (from 5 to 12 wt %). The effects of the process conditions on the membrane morphology have been evaluated, and structure-property relationships have been found. In all cases, the membranes exhibit interconnected structures with nanosized pores and high porosity, leading to reduced resistance to the gas mass transfer and high hydrophobic character of the surfaces. These membrane-like aerogels promise to form a new class of highly hydrophobic porous interfaces, potentially suitable to be used in membrane operations based, for example, on the contactor technology.

Advanced materials based on polymer cocrystalline forms

“…Monolithic high porosity s‐PS aerogels exhibiting three‐dimensional networks of highly crystalline nanofibers can be easily obtained by supercritical CO 2 extraction of the solvent present in physical gels 144–146. Similar polymeric aerogels have been also obtained for polysaccarides,147–149 poly(vinylidenefluoride‐ co ‐hexafluoropropylene),150 polyvinylidenefluoride,151 and isotactic poly‐4‐methyl‐pentene‐1 64…”

A Review on Porous Polymeric Membrane Preparation. Part I: Production Techniques with Polysulfone and Poly (Vinylidene Fluoride)

“…PVDF can be easily dissolved in common organic solvents such as N,N-Dimethylacetamide (DMAc), N,N-Dimethylformamide (DMF), Dimethylsulfoxide (DMSO), Hexamethyl phosphoramide (HMPA), N-Methyl-2-pyrrolidone (NMP), Tetramethylurea (TMU), Triethyl phosphate (TEP), Trimethyl phosphate (TMP), Acetone (Ac), DMF/Ac, methyl ethyl ketone (MEK) and Tetrahydrofuran (THF) [46,83,84]. To date, an emerging technique is to use supercritical carbon dioxide (sc-CO 2 ) as the non-solvent in the preparation of PVDF (see Table 3) as well as PS membranes [60,85,86,87,88,89]. This method can be considered as an improvement of the traditional phase inversion process because it is more environmentally friendly and has lower cost (recovery).…”

Crystalline polymorphism in poly(vinylidenefluoride) membranes

“…During P(VDF-co-HFP) membrane preparation using acetone and DMAc, respectively, as solvent [100], dipolar intermolecular interaction between P(VDF-co-HFP) and DMAc induced polar γ phase, which is absent (only the α phase is present) [101,102] or limited (α is present with few β and γ phases) [103] in the P(VDF-co-HFP) interatomic C-F bond so that the bond carries a permanent strong electric moment. This is believed to promote the electroactive phase formation.…”