Effect of polydispersity on the depletion interaction in nonadsorbing polymer solutions

The effect of polymer polydispersity on the depletion interaction between two plates immersed in a nonadsorbing polymer solution is studied by self-consistent-field theory. The depletion potential is calculated numerically for the Schulz molecular weight distribution. The results show that as the two plates approach the polymers with different chain lengths are excluded from the gap gradually for conformational entropy penalty, and the range of the depletion potential increases and the depth of the potential decreases with increasing polydispersity. For the case of two large spheres the Derjaguin approximation is used to study the effect of polydispersity. The result shows that the polydispersity has little effect on the contact potential. However, it induces more broad interaction than the monodisperse polymers.