Surface anti-biofouling control of PEGylated poly(vinylidene fluoride) membranes via vapor-induced phase separation processing

Influence of solvent composition and non-solvent activity on the crystalline morphology of PVDF membranes prepared by VIPS process and on their arising mechanical properties

“…However, totally different sizes of micro-domains were obtained. As far as the type of morphology is concerned, it has already been reported in at least four studies dealing with the preparation of PVDF membranes by VIPS process [8,9,21,22]. The formation of nodular structure is usually associated with a gelling initialized by crystallization: the crystalline domains grow freely before the onset on phase separation.…”

“…The consequence is a better control of membrane structuring with VIPS than by using LIPS, for which phase separation is quasi-instantaneous owing to the liquid/ liquid nature of the interface. Therefore, VIPS allows preparing a whole set of PVDF membrane structures from nodular morphologies [8] to bi-continuous matrices [9]. This can be achieved by carefully choosing and controlling the formulation parameters as well as the VIPS testing conditions.…”

“…By surveying literature, one will find that the essential parameters influencing the morphology of membranes prepared by VIPS are the casting solution composition and polymer concentration [10,11], the temperature of dissolution of polymer [9], the nonsolvent activity [12][13][14] and the exposure time to nonsolvent vapors [15][16][17]. Concerning more specifically the preparation of PVDF membranes by VIPS processing (and not combined to another process), less than ten studies have already been performed, most of them over the past three years, so that the knowledge of their formation remains incomplete [4,[7][8][9][18][19][20][21][22]. Because this is a semi-crystalline polymer, phase separation of PVDF solution involves a competition between crystallization and liquid-liquid demixing, and this is not clear up to now which one is favored when testing conditions -including solvent composition and nonsolvent activity -are varied.…”

“…Because this is a semi-crystalline polymer, phase separation of PVDF solution involves a competition between crystallization and liquid-liquid demixing, and this is not clear up to now which one is favored when testing conditions -including solvent composition and nonsolvent activity -are varied. In addition, a literature survey on these membranes reveals that only three solvents have been tested -dimethylformamide (DMF) [4,7,9,18], N-methylpyrrolidone (NMP) [8,9,19] and dimethylacetamide (DMAc) [9,20,21] and that the use of a co-solvent has not been reported yet in the preparation of PVDF membranes by VIPS process. Still, a change of solvent composition is a key formulation factor to control the structuring, by either delaying or promoting the onset of phase separation.…”

“…In this respect, the use of different solvents to cast PVDF membranes may lead to drastic changes as far as their essential properties such as mechanical properties are concerned. It was therefore surprising to notice that only LiCl [20], polyvinylpyrrolidone (PVP) [20] and triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene-oxide) (PEO-PPO-PEO) [8] solvent additives had been mentioned so far in the preparation of PVDF membranes by VIPS process. LiCl was used to enhance the protein adsorption, while amphiphilic copolymers PVP and PEO-PPO-PEO aimed at improving the hydrophilicity of PVDF membranes and decreasing biofouling owed to protein or bacterial attachment.…”