Scale-dependent diffusion of spheres in solutions of flexible and rigid polymers: mean square displacement and autocorrelation function for FCS and DLS measurements

Abstract

We present a theoretical description of diffusion of a sphere in polymer solution. The depletion layer around the sphere affects its motion and leads to scale-dependent diffusion. We propose the model of walking confined diffusion. Although it is different from anomalous diffusion, we show that the experimental data generated by this process may have features characteristic of anomalous diffusion. We give analytical formulas for the autocorrelation functions describing this type of motion in: i) dynamic light scattering experiments and ii) fluorescence correlation spectroscopy experiments. We compare our results to existing experimental data for polyethylene oxide, fd-virus, and F-actin solutions.