Tunable Nanoparticulate Scaffolds from Self assembly in Surfactant Mesophase

We examine the organization of silica nanoparticles in non-ionic surfactant, C$_{12}$E$_{9}$/water, H$_{1}$ phase. We show, using SAXS, TEM , Freeze Fracture and Microscopy, that particles with sizes smaller than the mesophase characteristic size, $a$, template the mesophase; particles with size $\sim \quad a$, partition into a dispersed phase and into strand-like aggregates. Particles of size $> \quad a$ phase separate to form particulate strands organized into a scaffold. The particulate network forms by expulsion of particles from growing H$_{1}$ phase domains; particles are concentrated in the isotropic phase and jam at domain boundaries. Changing the cooling rate into the H$_{1}$ phase changes the nucleation of domains -- hence providing a route to tune the network mesh size. When the surfactant is heated to the micellar phase, the particles redisperse readily. SANS confirms that C$_{12}$E$_{9}$ forms a bilayer on the silica particles, preventing their irreversible aggregation. PEI coated particles (with size $>a)$ also phase separate to form networks. The network of such coated particles can be crosslinked to obtain a free standing nanoparticulate scaffold.