“…Figure 7 shows a schema of the equilibrium phase diagram between the liquid and the crystalline solid of the PVDF-DMF binary system in the temperature range of our experiments, which is far below the equilibrium melting of PVDF (around 170ºC) [21] and far above the equilibrium melting of DMF (-61.2ºC) [22]. Assuming that no liquid-liquid phase separation takes place, an isothermal evaporation process starting with a 20 wt% solution of PVDF in DMF follows a horizontal line that crosses the equilibrium line separating the pure liquid from the solid-liquid biphasic region (solid line in Figure 7).…”
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.
“…Figure 7 shows a schema of the equilibrium phase diagram between the liquid and the crystalline solid of the PVDF-DMF binary system in the temperature range of our experiments, which is far below the equilibrium melting of PVDF (around 170ºC) [21] and far above the equilibrium melting of DMF (-61.2ºC) [22]. Assuming that no liquid-liquid phase separation takes place, an isothermal evaporation process starting with a 20 wt% solution of PVDF in DMF follows a horizontal line that crosses the equilibrium line separating the pure liquid from the solid-liquid biphasic region (solid line in Figure 7).…”
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.
“…When the cooling rate was − 10 K/min, a small difference was observed in the value of ΔH f (− 122 J/g), which is the enthalpy change in pure DMF molecules from an amorphous liquid state to a crystalline state, and ΔH m (128 J/g) is assumed due to the DSC measurement error. The literature values for the T m and ΔH m of DMF are 212.9 K (− 60.1 °C) and 122.4 J/g, respectively 31 . Figure 2 DSC graph obtained during the heating (red solid line) and quenching (blue dotted line) process for polymer solutions (PS/DMF) as a function of PS concentration and scan temperature.…”
The phase change temperature and enthalpy change as a function of polystyrene (PS) concentration in dimethylformamide through a dynamic heating and quenching process were investigated. Cold crystallization, freezing and melting phenomena in a 10 wt% PS solution were all observed. Cold crystallization and melting phenomena were still observed in a 20 wt% solution. In a 30 wt% solution, all three phenomena disappeared without any solvent enthalpy changes, e.g., enthalpy changes at the melting temperature. The disappearance of both the melting temperature and the melting enthalpy change indicated that all polymer and solvent molecules in the 30 wt% solution existed only in the amorphous phase without any phase changes despite repeated heating and quenching processes. Thus, our results can provide a new approach for gelation through enthalpy changes and can be applied in the fabrication of porous membranes with a narrow distribution.
“…The experimental density, speed of sound, refractive index and kinematic viscosity values, of the pure components at work temperatures and at p =0.1 MPa are collected in Table 2 along with isobaric expansibility values, calculated from our density measurements, and molar heat capacity values taken from literature [12][13]. For comparison, some values found in the literature [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] are also included in this Table.…”
Several thermophysical properties such as densities, ρ, speeds of sound, u, refractive indices, nD, and kinematic viscosities,, have been measured for the binary mixtures of N,N-Dimethylacetamide with 1-propanol and 1-butanol over the entire range of composition, at the temperatures (283.15, 298.15 and 313.15) K and at atmospheric pressure p = 0.1 MPa. From these experimental data, excess molar volumes, V E , excess isentropic compressibilities, E S , refractive index deviations, ΔnD, and viscosity deviations, Δη, were calculated. The calculated excess or deviation properties were correlated with the Redlich-Kister equation and the corresponding parameters were presented. The results obtained, were discussed in terms of structural effects and specific molecular interactions, and the influence of the alkanol chain length was also considered.
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