(271h) Network Percolation of Self-Assembled Bidisperse Colloidal Gels

Self-assembled colloidal depletion gels are important model systems for many industrial processes and applications, such as inks and pharmaceuticals. These nonequilibrium gels persist due to a dynamical arrest resulting in percolated structures with cluster-level architectures associated with the load-bearing capabilities of these materials. Although the relationship between the microstructure and rheological properties of self-assembled gels is well studied in gels composed of monodisperse colloids, introducing size polydispersity changes the network microstructure in ways that are not well understood. Here, we investigate the microstructure of fluorescent bidisperse poly(methyl methacrylate) colloidal gels comprising sterically stabilized poly(methyl methacrylate) (PMMA) particles (diameters 2a = 1.00 µm ± 4% and 2a = 1.49 µm ± 3%) mixed with polystyrene (M_w = 900,000 g/mol) as a depleting agent. Colloidal gels are synthesized at a range of volume fractions (0.1 < Ï• < 0.4) by suspending mixtures of bidisperse PMMA particles in a refractive index and density matched solvent. The non-equilibrium microstructures of the bidisperse gels are compared against monodisperse systems (2a = 1.20 µm ± 3%) with equivalent effective volume fractions. Confocal light scanning microscopy is used to obtain 3D image volumes from which particle centroids are detected and embedded as nodes for network analysis. The nearest neighbor distributions are separated into categories involving small-small, small-large, and large-large particle pairings. These distributions are further examined as a function of Ï• and gelation time scale, where differences between isotropic and isostatic percolation are expected to arise.