Reinforcement and Polymer Mobility in Silica–Latex Nanocomposites with Controlled Aggregation

Abstract

The tunable structure of silica–latex nanocomposites made of silica nanoparticles (radius ≈ 80 A) and a copolymer of methyl methacrylate and butyl acrylate–latex beads (radius ≈ 210 A) has been studied by small-angle neutron scattering and transmission electron microscopy. An aggregation diagram as a function of the control parameters—silica volume fraction and precursor solution pH—has been established. In this aggregation diagram, isoaggregation lines have been identified. It was used to express the small-strain reinforcement factor measured with stress–strain isotherms as a function of volume fraction at fixed aggregation number in the range from 50 to 100. The large-strain properties have been rationalized using the energy needed to rupture samples, and this quantity has been found to present an optimum at intermediate volume fractions (15%). In order to understand the striking rheology of the system, a neutron contrast-matching study has been undertaken by adding deuterated polymer beads. The bead de...