Thermal Diffusion of Dilute Polymer Solutions: The Role of Chain Flexibility and the Effective Segment Size

We have investigated the influence of the chain length and the size of the Kuhn segment on the thermal diffusion coefficient D T of dilute solutions of polymers in organic solvents. For oligomers and short polymer chains, D T increases with molar mass M and reaches a molar mass independent constant plateau value. A similar increase and plateau is observed for high polymers with increasing chain stiffness. For chains with Kuhn segments above 1 kg/mol, the plateau value is independent of the polymer and inversely proportional to the solvent viscosity. The thermal diffusion coefficient of such a polymer can be estimated to be D T ≈ 0.6 × 10−14 Pa m2 K−1 × η−1. No simple relation holds for short chains and flexible high polymers.