COLLOIDAL NATURE OF STAR POLYMER DILUTE AND SEMIDILUTE SOLUTIONS

The structure of dilute and semidilute solutions of 8-, 12-, and 18-arm star-branched polyisoprenes and 12-arm polystyrenes in good solvent conditions was studied by small-angle neutron scattering (SANS). Interparticle interactions influence the low-angle scattering at concentrations well below the overlap concentration, c*. We have found in the semidilute solutions evidence for interparticle repulsion and a corresponding depression in the structure factor S(q) at low q. A function for fitting the scattering data from stars is introduced which allows a precise determination of the radius of gyration even at concentrations that are a finite fraction of c*. The method was also used to fit results from computer simulations and its usefulness compared to the commonly used Kratky plot method.