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Differential scanning calorimetric study of phase changes in poly(ethylene glycol) dodecyl ether-water systems
Authors:B Andersson  G Olofsson
Institution:(1) Present address: Division of Thermochemistry, Chemical Center, University of Lund, Lund, Sweden
Abstract:Phase changes in binary systems of poly(ethylene glycol) dodecyl ethers, C12H25(OC2H4)xOH (x=5, 6 and 8) with water have been studied between –40 to 100 DaggerC by differential scanning calorimetry. A number of transitions, including the liquidliquid phase separation, were seen and the transition temperatures and enthalpy changes were determined. The observed temperatures were generally in good agreement with reported phase diagrams. In the C12E5 system, three of the four three-phase lines were seen and a more complete phase diagram is suggested for the water-rich part of the system. Most of the phase changes seen above 0 DaggerC are accompanied by small endothermic enthalpy changes of 0.7 to 0.9 kJ (mol C12Ex)–1, independent of system studied, type of transition and transition temperature. Water-rich solutions and liquid crystalline phases separate upon freezing into ice and crystals of hydrated amphiphile. Eutectics are developed at the following temperatures and compositions: C12E5 –3.0 DaggerC and 54 wt % C12E5; Q2E6 –4.5 DaggerC and 54 wt % C12E6, C12E8 –3.8 DaggerC and 49 wt % C12E8.
Keywords:Phase changes  transition enthalpies
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