Abstract
Translational diffusion coefficients of two narrow molecular weight distributions of polystyrene in cyclohexane under theta conditions have been studied using Rayleigh linewidth spectroscopy. Experimental evaluation of the time correlation function profiles according to the histogram approximation shows that the diffusion coefficient at zero concentration ( D 0) and the concentration dependence of the first-order friction coefficient ( k f ) can be determined by making only one measurement of the time correlation function of a polymer solution of known molecular weight (such as M ̄ z , M ̄ w or M ̄ n ) at one concentration and one scattering angle. By making photon correlation measurements at two different concentrations, we are able to make a definitive comparison of our experiments with the theoretical descriptions of Yamakawa, Imai, and Pyun and Fixman. In contrast to earlier findings of King, Knox, Lee and McAdam ( Polymer 1973, 14, 151), our results are in excellent agreement with the theoretical prediction of Pyun and Fixman at the theta temperature.
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