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) cm2(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).