Structure and dynamics in dense suspensions of micellar nanocolloids

We present an experimental description of the dynamics of a dense colloidal suspension of model hairy nanoparticles using dynamic light scattering. These colloids were obtained by cross-linking the poly(2-cinnamoylethyl methacrylate) cores of polystyrene-block-poly(2-cinnamoylethyl methacrylate), copolymer micelles. Because of their small size and the small spacing of their liquidlike structure, as detected with small-angle neutron scattering, these particles enable the systematic investigation of the low-scattering wavevector (q) fraction of the dynamic structure factor (S(q,t)) away from the peak, which relates to the osmotic modulus of the suspension. The two relaxation processes contributing to S(q,t) are the fast cooperative diffusion of the concentration fluctuations (hair interactions) and the self-diffusion of the slightly polydisperse cores (incoherent contribution). The former speeds up and loses intensity with increasing concentration, analogous to linear and hyperstar polymer solutions, whereas the latter slows down and exhibits virtually increasing intensity with concentration as a consequence of the correlation hole at low q's, much like the hard sphere colloids. The study of these hairy particles contributes to the overall picture of the dynamic response of concentrated colloidal suspensions sterically stabilized by grafted macromolecules.