Poly[(vinylidene fluoride)‐co‐trifluoroethylene] Membranes Obtained by Isothermal Crystallization from Solution

Abstract

Electroactive macroporous poly[(vinylidene fluoride)‐co‐trifluoroethylene] membranes have been produced by solvent evaporation at room temperature, starting with a diluted solution of the copolymer in dimethylformamide. The pore architecture consists of interconnected spherical pores. This architecture is independent of the membrane thickness. The thickness of the membranes ranges from a few to several hundred µm, using spin coating and evaporation in static conditions, respectively. The pore structure is explained by a spinodal decomposition of the liquid/liquid phase separation and crystallization in the copolymer‐rich phase.magnified image

Tailoring porous structure of ferroelectric poly(vinylidene fluoride-trifluoroethylene) by controlling solvent/polymer ratio and solvent evaporation rate

“…The determination of the kinetic parameters over a series of weight losses has more accuracy than the method of the "general rate expression". Flynn developed a method to calculate the kinetic parameters at different conversion levels using isothermal techniques [10][11][12][13][14][15][16][17][18][19]:…”

“…As the spherulite grows, more polymer in the liquid state will be joined to the crystallization interface and, at the end, when no liquid are present in the interface between spherulites, a open space will be left giving origin to the small pores appearing among the spherulites. produced by TIPS from a solution in a solvent/nonsolvent mixture [7,10,12,13,22].…”

“…The shape of the phase diagram in the region of the liquid/liquid coexistence region can be predicted with the help of the Flory-Huggins (FH) lattice teory [13].…”

“…In the SD region, small variations in the composition destabilizes the system, separating it into two phases with lower free energy. In the metastable region a large flutuation in the composition is needed to create a domain larger than some crtical ratio, in order to enable the NG process [13,24].…”

“…Through it has been previously proven that the isothermal evaporation from a homogeneous P(VDF-TrFE) copolymer solution produce a well-organized porous structure in membranes from 1 to 250 m [13], the different experimetal conditions that can allow tayloring membrane characteristics have not been explored and the mechanism responsible for the pattern fomation has to be further explained.…”