Translational diffusion of 12-arm star polystyrenes in dilute and concentrated poly(vinyl methyl ether) solutions

The technique of dynamic light scattering from isorefractive ternary solutions has been used to study the translational diffusion behaviour of 12-arm star polystyrenes (PS) in dilute and concentrated solutions of poly(vinyl methyl ether) (PVME). PS molecular weights ranged from 5.5 × 10⁴ to 1.69 × 10⁶. The PVME molecular weight was 1.4 × 10⁵, and the PVME concentration was varied from 0.001 to 0.30 g ml^-1. The concentration dependence of diffusion is well described by the functional form D D₀ = exp(-ac^u), although there is some evidence that the star dimensions decrease with increasing PVME concentration. Comparison with the diffusion behaviour of linear PS in PVME solutions suggests that, for these molecular weights of PS and PVME, the diffusant topology is not important, and thus reptation is not a significant mechanism under these conditions. At the same time, neither the Stokes-Einstein relation nor a simple scaling function, f( R ξ), can describe the observed behaviour. These results are interpreted as reflecting substantial PVME mobility, relative to the PS stars.