On the radius of gyration of macromolecules in semi‐dilute solutions

Abstract

AbstractFrom the shape of the curves of scattered light intensity plotted against sin2θ/2 where θ is the scattering angle, one may estimate the concentration interval where one surpasses the upper bounds of the dilute solution and enters into the semi‐dilute solution region. This transition interval, approximating C*, is at a concentration where the large‐angle part of the curve flattens out and does not yet show a concavity in the small angle part of the curve. This concavity appears in the semi‐dilute region at C>C* and is shown to be strongly dependent on molecular aggregation at these concentrations. The aggregation effects were demonstrated by means of filtration through various pore sizes, and by mixing visible iodized polystyrene (PS) with invisible PS in bromoform.It is further shown that the apparent radius of gyration (RG) obtained from dissymmetry measurements change as a function of concentration, passing through a minimum at a concentration C = C*. It is proposed that C* may be experimentally determined from either the flatness of the scattered light intensity curves, or from the minimum in the curves of apparent RG as obtained from dissymmetry measurements.