Diffusion of hairy polymeric micelles in a homopolymer solution

Polystyrene-block-poly(4-vinylpyridine) (PS-b-PVP) forms hairy micelles with PVP and long PS block as the core and corona in toluene, respectively. Diffusion of the micelles in solution in the presence of poly(methyl methacrylate) (PMMA) or polystyrene homopolymer (h-PS), from dilute to semidilute, has been investigated by laser light scattering (LLS). Our results indicate the micelles only exhibit translational diffusion with characteristic Γ = Dq² in PMMA dilute and semidilute solutions, where Γ, D and q are characteristic line width, translational diffusion coefficient and scattering vector, respectively. PMMA concentration dependence of D reveals that the micelle diffusion follows a “stretched exponential” scaling law, similar to that of a hard sphere in the presence of matrix polymer. This is because the PS corona is incompatible with PMMA and no entanglement between them occurs. In contrast, in h-PS solution, due to the overlap and entanglement between the PS corona and h-PS matrix, the micelles exhibit diffusion with characteristic of Γ ∝ q^α, where α = 2-2.6. For the same matrix polymer concentration, the micelles exhibit a faster diffusion in PMMA solution than that in h-PS solution, especially in semidilute solutions. The fact further indicates that the overlap and entanglement between the corona and h-PS matrix restrict the micelle motion.