SELF-DIFFUSION - AN EXPERIMENTAL DEMONSTRATION OF THE NON-APPLICABILITY OF THE REPTATION MODEL TO SEMIDILUTE POLYMER-SOLUTIONS

The translational diffusion of probe chains in ternary systems has been measured in the homopolymeric polyisobutylene (PIB) system: PIB1/PIB2/chloroform. In the crossover region, dilute/semidilute, a universal curve is found with logarithmic ( D D0)probe versus ( C C*)matrix plots. Data for Mprobe ≫ Mmatrix and Mmatrix ≫ Mprobe follow the same relationship as those for hard spheres in the same systems. In semidilute solutions, a universal curve is found with logarithmic plots of (DM)proble versus ( C C*)matrix. These data establish that the reptation/scaling model is inapplicable in semidilute solutions even though the scaling predictions are fulfilled over the concentration interval employed. Recent theories for cooperative chain motion are seen to be the most promising means of describing the dynamics in congested solutions. © 1990.