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

In this work we study the molar mass dependence of the thermodiffusion of polyethylene oxide at different temperatures in ethanol, water/ethanol mixture (c_water=0.7) and water in a molar mass range up to M_w=180000 g/mol. Due to the low solubility of polyethylene oxide oligomers in ethanol the measurements are limited up to M_w=2200 g/mol. The specific water/ethanol concentration 0.7 has been chosen, because at this weight fraction the thermal diffusion coefficient, D_T, of water/ethanol vanishes so that the system can be treated as a pseudo binary mixture. The addition of ethanol will degrade the solvent quality, so that we expect a change of the interaction energies between polymer and solvent. The analysis of the experimental data within a theoretical model shows the need of a refined model, which takes specific interactions into account