Theory of static scattering from polymer mixtures. The case of polystyrene/polydimethylsiloxane/poly(methyl methacrylate)/toluene

The static scattering properties of four-component polymer mixtures are examined starting from the general equation extending the random phase approximation to multicomponent systems first proposed by Benoit. The results are compared with the light scattering data reported recently by Strazielle and coworkers for polystyrene/polydimethylsiloxane/poly(methyl methacrylate)/toluene mixtures. The present formalism provides a more rigorous treatment of these data, and a good agreement is obtained without adjustable parameters. This method provides a definition of the apparent interaction parameter used by Strazielle et al. and describes its correlation with various relevant quantities characterizing the mixture. It predicts in particular the variation of this parameter with the concentration of poly(methyl methacrylate), which was not possible in the earlier work. Various other important properties of the mixture are investigated such as the critical concentration for phase separation and the apparent radius of gyration.