Abstract

We present measurements of aqueous low molecular weight mixtures and aqueous macromolecular solutions. The Soret coefficient S _T for ethanol, acetone, and DMSO in water was measured by an optical grating technique, and all systems showed a sign change around a molar fraction of water x _water = 0.85 ± 0.05. S _T for poly(ethylene oxide), poly(N-isopropylacrylamide), and boehmite rods in ethanol/water mixtures showed also a sign change close to the same concentration. The occurring sign change concentration in the systems will be related to structural reorganizations in the solvent mixture and the Hildebrandt solubility parameter. We will also compare the experimental data within lattice calculations and simulations, which indicate that strong cross-interactions are important for a sign change of the Soret coefficient.