COMPARISON OF VARIOUS MEASUREMENTS OF MICROSCOPIC FRICTION IN POLYMER-SOLUTIONS

Six measurements of microscopic friction in polystyrene/tetrahydrofuran (THF) solutions are compared. Microscopic friction is inferred from the degree to which rigid probe molecules rotate or translate more slowly as the polymer concentration is increased. The fluorescence anisotropy decay method is used to measure rotational dynamics of anthracene and 9,10-bis(phenylethynyl)anthracene. NMR techniques (T1 and PGSE) are employed to monitor rotational and translational diffusion of the solvent. These four measurements are supplemented by rotational diffusion data for 9,10-diphenylanthracene and translational diffusion coefficients of methyl red, available in the literature. All measurements span similar concentration (0-70 % polymer) and temperature (5-45-degrees-C) ranges. Dynamics of the four largest probes follow a common polymer concentration dependence. At each concentration they have a common temperature dependence, shared also by the temperature dependence of the viscosity of a closely related system. Dynamics of THF have weaker concentration and temperature dependences. In addition, THF rotational diffusion follows a different concentration dependence than THF translational diffusion. These trends are discussed in terms of probe size. Comparisons are made to dynamics in polystyrene solutions with other solvents.