Effect of Dispersity on the Conformation of Spherical Polymer Brushes.

We show that dispersity ( D̵ ) markedly alters the conformation of spherical polymer brushes. The average lengths ( l b ) of poly( tert -butyl acrylate) (P t BA) brushes of varying D̵ grafted to nanoparticles were measured using dynamic light scattering. In the semidilute polymer brush (SDPB) regime, the l b of P t BA and polymers from earlier studies of various D̵ could be cleanly collapsed onto a master curve as a function of the scaling variable N w σ 1/3 , where N w is the weight-average degree of polymerization and σ is the grafting density. In the concentrated polymer brush (CPB) regime, however, l b collapsed onto a bifurcated curve as a function of the scaling variable N w σ 1/2 , indicating D̵ more strongly affects the average length of brushes with low N w σ 1/2 . We propose that the stretching of the stem near the particle surface due to interchain interactions in the CPB regime leads to greater l b in broad dispersity brushes of low but not high N w σ 1/2 .