Correlation between the Soret coefficient and the static structure factor in a polymer blend

Mutual mass diffusion and thermal diffusion has been investigated in poly(dimethylsiloxane)/poly(ethylmethylsiloxane) (PDMS/PEMS) polymer blends of equal weight fractions. Molar masses ranged from below 1 to over 20 kg/mol. Both the mutual mass (D) and the thermal diffusion (D-T) coefficient contain a thermally activated factor with an activation temperature of 1415 K. The molar mass dependence of D-T is due to an end-group effect of the local friction coefficient. The thermal diffusion coefficient in the limit of long chains and infinite temperature is D-T(0,infinity) = -1.69 x 10(-7) cm(2)(sK)(-1). The Soret coefficient S-T of blends far enough away from a critical point is proportional to the static structure factor S(q = 0).