Modes of deformation in a soft hard nanocomposite: A SANS study

Nanocomposites have been made by mixing soft particles (polymer latex) with hard particles (silica) in aqueous dispersions and extracting water to pro duce a dense film. Segregation between the two kinds of particles can be co ntrolled, and even suppressed. The elongational modulus is strongly increas ed by such fillers at low deformations, and remains important at large defo rmations, which the samples can stand without breaking. Since the silica pa rticles are small (200 Angstrom), we can follow their relative displacement s under stretching, by Small-Angle Neutron Scattering, through analysis and simulation of the anisotropic patterns. The latter show a crossover from a ffine displacements to a set of shear displacements that let the particles avoid each other at large deformations. The shear could release the localis ed stresses (due do polymer confinement) and dissipate more energy. In this way it may contribute to the toughness of the composite against crack prop agation.