Thermally induced phase separation of poly(vinylidene fluoride)/diluent systems: Optical microscope and infrared spectroscopy studies

Abstract

Thermally induced phase separation (TIPS) has been developed to prepare porous membranes. The porous structures are mainly dependent on diluents adopted in the TIPS process. We obtained two typical morphologies of poly(vinylidene fluoride) (PVDF) membranes using cyclohexanone (CO) and propylene carbonate (PC) as diluents, respectively. SEM observation displays that porous spherulites are formed from PVDF/CO system, whereas smooth particles result from PVDF/PC system. The TIPS processes of these two systems have been investigated in detail by optical microscope observation and temperature‐dependent FTIR combined with two‐dimensional infrared correlation analysis. Rapid crystallization of PVDF can be seen around 110 °C in the PVDF/CO system, which is consistent with the results of temperature‐dependent FTIR spectra. The spectral evolution indicates a transform of PVDF from amorphous to α‐phase after 110 °C. The νs(CO) band at 1712 cm−1 narrows and the νs(CF) band at 1188 cm−1 shifts to 1192 cm−1 before crystallization, which implies the destruction of interaction between PVDF and CO. In contrast, the PVDF/PC system shows slow crystallization with all‐trans conformation assigned to β‐phase and γ‐phase below 60 °C but no obvious change of polymer−diluent interaction. We propose two mechanisms for the different phase behaviors of PVDF/CO and PVDF/PC systems: a solid−liquid phase separation after destruction of polymer−diluent interaction in the former, and a liquid−liquid phase separation process coupled with rich‐phase crystallization in the later. This work may provide new insight into the relationship among morphologies, crystal forms, and phase separation processes, which will be helpful to adjust membrane structure. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1438–1447

Fabrication of Porous Materials from Natural/Synthetic Biopolymers and Their Composites

“…As diluent is closely related to phase separation, different diluent cause different pore structures [77]. The advantages of this method are simplicity of the process, high reproducibility, low defects rate, high porosity and narrow pore size distribution [78].…”

Suppressing loss tangent with significantly enhanced dielectric permittivity of poly(vinylidene fluoride) by filling with Au–Na1/2Y1/2Cu3Ti4O12 hybrid particles

“…22,23 At the same time appear bands at 841 and 1275 cm À1 , characteristic for b-phase. 22,23 Moreover, the bands at 613, 762, 874 and 1275 cm À1 were attributed to the CCC skeletal bending vibration. The characteristic bands at 874, 1071 and 1275 cm À1 were assigned to the CC skeletal symmetric stretching vibration, while the bands at 841, 874, 1177 and 1275 cm À1 were assigned to the CF 2 symmetric stretching vibration.…”

“…7,21 The characteristic bands of a-phase were observed at 613, 762, 797, 874, 976, 1071, 1177 and 1398 cm À1 . [22][23][24] The band at 841 cm À1 , assigned to the gphase. 22,23 At the same time appear bands at 841 and 1275 cm À1 , characteristic for b-phase.…”

“…[22][23][24] The band at 841 cm À1 , assigned to the gphase. 22,23 At the same time appear bands at 841 and 1275 cm À1 , characteristic for b-phase. 22,23 Moreover, the bands at 613, 762, 874 and 1275 cm À1 were attributed to the CCC skeletal bending vibration.…”

Structural and dielectric properties of hot-pressed poly(vinylidene fluoride)-based composites

“…Bands at 615, 766, 795, 874, 974, 1070, 1148, 1182, 1210, 1383, 1402, 1432 and 1455 cm −1 can be associated to α-phase, whereas bands at 840, 882 and 1275 cm −1 are fingerprints of β-phase. 14,16–18 Interestingly, a small signal at 1235 cm −1 corresponding to γ-phase is also detected. From these results, it can be concluded that both samples majorly have the α-crystal phase and β-phase in a less degree.…”