J. Phys. II France
Volume 6, Numéro 12, December 1996
Page(s) 1781 - 1795
DOI: 10.1051/jp2:1996160
J. Phys. II France 6 (1996) 1781-1795

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

M. Adam1, J.-P. Carton2, S. Corona-Vallet1 and D. Lairez1

1  Laboratoire Léon Brillouin, CEA-CNRS, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
2  Service de Physique de l'État Condensé, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France

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

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 $T_\theta = 70~^\circ$C. The molecular mass of the copolymer is $1.1 \times 10^6$ 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 ${\rm g/cm}^3$. 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.

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