The surface-tethering of polymeric chains has emerged as an effective means to enhance the mechanical properties and workability of particle solids. The objective of this project was to elucidate the role of grafting density on the mechanical properties of particle solids that are subject to small and large strains. A library of silica particles tethered with polystyrene (PS) and poly(methyl methacrylate) (PMMA) and systematically controlled density and degree of polymerization of tethered chains was synthesized using surface-initiated atom transfer radical polymerization (SI-ATRP). The elastic modulus and fracture toughness were evaluated using nanoindentation in thick particle arrays. Particle brush materials with dense and intermediate grafting density show similar structures and trends in mechanical property. Polymer tethers in the limit of intermediate grafting density were found to be more effective in ‘stiffening’ the particle solid. This effect was attributed to the higher entanglement density of intermediate brush systems. Interestingly, particles in the sparse analog form string-like connected structures which are attributed to the prevalence of particle surface-surface interactions. As a result, the surface graft density is an important parameter governing particle brush architecture and mechanical property. The intermediate density materials suggest possible applications for colloidal materials that enable highly efficient and mechanically robust nanocomposite materials with high inorganic content.<br/>

Enhancement of mechanical property with self-assembled particle brush materials

256th National Meeting (2018)

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