(383d) Structural Studies of Mixtures of Colloidal Semi-Flexible Rods (polyelectrolyte-surfactant aggregates) and Spheres

The interaction of a polyelectrolyte-surfactant aggregate with semi-flexible rod morphology and silica spheres of different sizes in aqueous environment had been studied using small angle neutron scattering (SANS). The rod-like aggregates have dimensions of 4nm by140nm while the negatively-charged silica spheres range from 2nm to 170nm. This range of relative sizes allows for three possible structures in mixed systems: 1) non-interacting spheres and rods, 2) aggregate covered by silica spheres ? taking on a core-shell cylinder morphology, and 3) silica covered by a layer of aggregates ? taking on core-shell sphere morphology. We report on a series of contrast matched neutron scattering studies that elucidate the different morphologies as a function of increasing silica size. Solution stability is verified and shown to increase as the size of the silica increases. Preliminary analysis indicates that there is association between aggregates and silica as predicted, and the rod wraps around the silica spheres, even for silica comparable to the radius of the rods. The strong attraction between the rod and the spheres, together with the intrinsic flexibility of the aggregate, is enough to overcome the bending energy required for this morphology to exist. The impact of the morphology on phase stability and macroscopic behaviors will be discussed in the context of the structural characterization.