Molar mass and temperature dependence of the thermodifusion of polyethylene oxide in water/ethanol mixtures

In this work we study the molar mass dependence of the thermodiffusion of polyethylene oxide atdifferent temperatures in water, ethanol and in a water/ethanol mixture (C_water = 0.7) in a molar massrange up to Mw=180000 g/mol. Due to the low solubility of polyethylene oxide oligomers in ethanol themeasurements are limited up to Mw=2200 g/mol. The specific water/ethanol concentration 0.7 is chosen,because at this weight fraction the thermal diffusion coefficient, D_T, of water/ethanol vanishes so thatthe system can be treated as a pseudo binary mixtures. The addition of ethanol will degrade the solventquality, so that we expect a change in the interaction energies, which can be calculated using a modelderived by Würger [1]. We also found that with adding ethanol to water, the thermodiffusion behavior ofPEO changes from thermophobic to thermophilic