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 produce a dense film. Segregation between the two kinds of particles can be controlled, and even suppressed. The elongational modulus is strongly increased by such fillers at low deformations, and remains important at large deformations, which the samples can stand without breaking. Since the silica particles are small (200 Å), we can follow their relative displacements under stretching, by Small-Angle Neutron Scattering, through analysis and simulation of the anisotropic patterns. The latter show a crossover from affine displacements to a set of shear displacements that let the particles avoid each other at large deformations. The shear could release the localized stresses (due to polymer confinement) and dissipate more energy. In this way it may contribute to the toughness of the composite against crack propagation.