One-dimensional diffusion of colloids in polymer solutions

For colloid-polymer systems confined in one-dimensional channels, the diffusion of the colloidal particles is obtained by tracking individual particles using enhanced video microscopy and digital image analysis. For short times, the diffusion is normal, of the Fickian type, with mean-squared displacement varying linearly with time. For long times, however, the mean-squared displacement is found to increase more slowly with time, being proportional to the square root of time, in agreement with the theoretical prediction for diffusion of hard rods in one dimension in which mutual crossing of the particles cannot take place. The crossover from short-time to long-time diffusion is observed and is found to depend on the colloid and polymer concentrations. Unexpectedly, for small polymer-to-colloid size ratios, it is the polymer rather than the colloid concentration which has a leading effect on the colloid diffusion.