Effect of Dispersity on the Conformation of Spherical Polymer Brushes.

Abstract

We show that dispersity (D̵) markedly alters the conformation of spherical polymer brushes. The average lengths (lb) of poly(tert-butyl acrylate) (PtBA) brushes of varying D̵ grafted to nanoparticles were measured using dynamic light scattering. In the semidilute polymer brush (SDPB) regime, the lb of PtBA and polymers from earlier studies of various D̵ could be cleanly collapsed onto a master curve as a function of the scaling variable Nwσ1/3, where Nw is the weight-average degree of polymerization and σ is the grafting density. In the concentrated polymer brush (CPB) regime, however, lb collapsed onto a bifurcated curve as a function of the scaling variable Nwσ1/2, indicating D̵ more strongly affects the average length of brushes with low Nwσ1/2. We propose that the stretching of the stem near the particle surface due to interchain interactions in the CPB regime leads to greater lb in broad dispersity brushes of low but not high Nwσ1/2.