α to β Phase Transformation and Microestructural Changes of PVDF Films Induced by Uniaxial Stretch

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

“…Characteristic absorption bands from the -phase have been identified at 840, 745, 510, and 445 cm −1 . One can also clearly observe the absence of -phase (408, 532, 614, 764, 796, 855 and 976 cm -1 ) or -PVDF (431, 776, 812 and 833 cm -1 ) characteristic bands [3,6]. These results were observed for all samples, showing that if the crystallization temperature is lower than 70 ºC, the polymer crystallizes only in the electroactive -phase [3,5,6].…”

“…Phase separation of the polymer solution for the preparation of porous membranes can be induced by several methods, such as immersion precipitation, air-casting of the polymer solution, precipitation from the vapour phase, and thermally induced phase separation (TIPS) [3,11]. A few works have been reported on preparation of PVDF microporous membrane via TIPS [3,11,14,16,17].…”

“…The one with the best piezo-, pyro-, and ferroelectric properties is the -phase [1,2]. Until recently, this phase was exclusively obtained by mechanical stretching of films originally in the non-polar -phase, which is the most stable one from a thermodynamic point of view when the material is directly obtained from the melt [1,3]. The stretching process results in films mostly in the -phase, but with a small amount of the material in the -phase [3].…”

“…A few works have been reported on preparation of PVDF microporous membrane via TIPS [3,11,14,16,17]. TIPS has proven to be a valuable method for making commercial membranes.…”

“…Until recently, this phase was exclusively obtained by mechanical stretching of films originally in the non-polar -phase, which is the most stable one from a thermodynamic point of view when the material is directly obtained from the melt [1,3]. The stretching process results in films mostly in the -phase, but with a small amount of the material in the -phase [3]. Un-oriented films exclusively in the  phase can also be obtained from the crystallization of PVDF from solution with N,N-dimethylformamide (DMF) or dimethylacetamide (DMA) at temperatures below 70 ºC [4,5].…”