The determination of chain statistical parameters by light scattering measurements

Abstract

The effects of volume exclusion on polymer chain conformations can be determined from the study of the angular dependence of radiation scattered by chain molecules. It is found that useful information can be obtained only when the variable x is large, where x is the product of the square of the magnitude of the scattering vector and of the mean square radius of gyration. Hence, solutions of macromolecules of very high molecular weight are needed for these investigations. The theoretical treatment of the scattering function is based on several assumptions. The validity of these assumptions is examined by computing, using a Monte-Carlo technique, various moments of intramolecular separations and comparing the results so obtained, in the limit of a chain of infinite length, with the analytical results. The computations seem to verify the validity of the theoretical model. The scattering behavior of solutions of recently synthesized polystyrene of Mw = 4.4 X 10(7) in cyclohexane at various temperatures and in benzene at 40 degrees was investigated. From the log-log plots of the scattering function vs. x, a statistical parameter was calculated, whose value depends on the magnitude of long-range correlations between any pair of chain elements. It is found that above the theta temperature this parameter is practically independent of temperature and that its numerical value was found to agree well with the value obtained from Monte-Carlo calculations. In the neighborhood of the theta temperature, this parameter decreases rapidly with decreasing temperature, indicating a first-order transition in chain conformation.