Characterization of Polymer Solutions Containing a Small Amount of Aggregates by Static and Dynamic Light Scattering

Aggregate-containing solutions of poly( n -hexyl isocyanate) (PHIC) and atactic polystyrene of finite concentrations were studied by static and dynamic light scattering. Their static structure factors Ŝ ( k ) and the intensity autocorrelation functions g (2) ( t ) exhibited the enhanced low-angle scattering and bimodal relaxation, respectively. From Ŝ ( k ) and g (2) ( t ) obtained, the fast- and slow-mode components of the static structure factor ( Ŝ fast ( k ) and Ŝ slow ( k )) and of the first cumulant (Γ fast and Γ slow ) were estimated as functions of the magnitude of the scattering vector k . As verified by a theory based on the dynamic mean-field theory, if the solution contains only a small amount of aggregates with diffusion coefficients much smaller than that of the nonaggregating component, Ŝ fast ( k ) and Γ fast give us the osmotic compressibility ∂ c /∂Π and mutual diffusion coefficient D m of aggregate-free solutions, respectively, and Ŝ slow ( k ) and Γ slow provide us the radius of gyration 〈 S 2 〉 z, A 1/2 and hydrodynamic radius R H,A of aggregates, respectively, even at a finite polymer concentration, in a good approximation. In fact, the results of ∂ c /∂Π and D m obtained were favorably compared with theories for binary polymer solutions without aggregates. For PHIC solutions, aggregates of lower molecular weight samples had larger 〈 S 2 〉 z, A 1/2 and R H,A, indicating that the aggregates of lower molecular weight PHIC consist of a larger number of polymer chains. Furthermore, the ratio of 〈 S 2 〉 z, A 1/2 to R H,A indicated that aggregates of higher-molecular-weight PHIC are rigid-chain-like but those of lower-molecular-weight PHIC are spherelike.