Dilute Solutions of Diblock Copolymers in a Selective Solvent: I. Evidence for Spherical Star like Micelles

(Received 16 April 1996, received in final form 29 August 1996, accepted 2 September 1996)

Abstract
Diblock copolymer polystyrene-polyisoprene PS-PI is studied in dilute solution at room temperature in methylcyclohexane, a good solvent for polyisoprene and a theta solvent for polystyrene at C. The molecular mass of the copolymer is g/mol and the polystyrene weight fraction is 36%. The diblock copolymer aggregates into star like micelles which are studied by static and quasielastic light scattering. Both techniques lead to a full characterization of the micelles. Well below the overlap concentration, the data are strongly dependent on micelle interactions. The scattered intensity (the diffusion coefficient) presents a maximum (a minimum) at a scattering vector which is concentration dependent. From this dependence we infer that the micelles are in a liquid phase, the mean distance between first neighbor being 400 nm at a concentration C = 10^-3 . From these measurements we can deduce the mobility per monomer and demonstrate that the micelles move in an effective medium having the macroscopic viscosity of the solution.