Transport of probe particles in semidilute polymer solutions

Dynamic light scattering and sedimentation measurements are carried out to study the motion of probe particles in neutral and adsorbing polymer solutions. By varying the microscopic interaction between the colloidal particle and the polymer molecule, we observe three different behaviors to the Stokes-Einstein (SE) equation in the same colloid-polymer system. The measurements clearly delineate the sample conditions under which the three different behaviors are observed, respectively. It is shown that the three different behaviors can be explained consistently in terms of the microstructures formed in the colloid-polymer mixture. The experiment demonstrates the importance of restraining the particle-medium interaction in the measurement of the microrheological properties of complex fluids.