The effect of concentration on diffusion coefficient in polymer solutions

A microinterferometric method was used to measure the diffusion coefficient as a function of concentration in the system dimethylformamide‐polyacrylonitrile at 25°C. The diffusion coefficient increases with increasing polymer concentration up to the maximum employed, 17.72% by weight. The theoretical basis for this type of behavior is explained. The diffusion coefficient in the limit as the polymer concentration approaches zero was calculated from theory to be 0.30 × 10−6 sq.cm./sec. This value is consistent with the diffusion coefficients obtained experimentally.