The Role of Solvent Evaporation in the Microstructure of Electroactive β-Poly(Vinylidene Fluoride) Membranes Obtained by Isothermal Crystallization

Abstract

Electroactive -poly(vinylidene fluoride) membranes were obtained by isothermal crystallization from the solution. Different morphologies and microstructures were obtained by crystallizing at different temperatures. The mechanism and kinetics of solvent evaporation from the polymeric solution were investigated using isothermal thermogravimetric analysis. The kinetic parameters and the activation energy were also 2 calculated. The solvent evaporation is ruled by two steps, related with a metastableunstable -metastable transition in the solution phase diagram. Scanning electron microscopy revealed the porous structure and the variations of the morphology with the variation of the isothermal evaporation temperature. Finally, the infrared spectroscopy measurements confirm that the polymer crystallizes in the electroactive -phase of PVDF.

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

“…Furthermore, the derivative of the weight loss curves is larger for higher temperatures, showing the increase of the evaporation rate with increasing temperature, while it decreases with time due to the progressive increase of solvent concentration during the evaporation process. This behaviour was already observed in the homopolymer PVDF [15]. in this approach, evaporation appears as a zero order thermally activated process, a feature that is coincident with our finding for the solvent evaporation.…”

“…On the other hand, as temperature increases, this phenomenon is more pronounced, and in fact at 60 ºC nearly no presence of the macropores originated in liquid-liquid phase separation are observed in the dry material. The structure is then nearly the same than that produced in PVDF by liquidsolid phase transition [15].…”

“…In the TGA experiments the weight-loss, α, is given by [15,16] (t) and w ∞ are the weights of the sample before solvent evaporation, at a given time t and after complete drying, respectively. An analysis of the kinetics of solvent evaporation can be performed in terms of the general equation [16]:…”

“…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]:…”

Fiber average size and distribution dependence on the electrospinning parameters of poly(vinylidene fluoride–trifluoroethylene) membranes for biomedical applications

“…These defects are typically related to the slow evaporation rate of the solvent during the travelling from the tip to the collector, due to the high DMF boiling point (153 ºC, table 1) [13]. In order to obtain well-formed fibers and samples without beads, a mixture of DMF and MEK solvents was used to dissolve the P(VDF-TrFE) polymer.…”