Structure and rheological properties of latex-silica nanocomposite films: Stress-strain isotherms

A study of the rheological properties of. silica-filled nanolatex films by means of uniaxial strain experiments is presented. The samples are made by evaporating the aqueous solvent of mixtures of colloidal silica and colloidal nanolatex, followed by film formation. The reinforcement effect due to the introduction of hard silica beads is investigated as a function of silica volume fraction 4), pH in solution before film formation, and silica bead size. The stress-strain curves show that the material can be stretched up to high elongations typically around four or more before rupture, indicating that the extensibility of the pure nanolatex film is conserved. It is found that the silica contributes differently at small and large deformations: In the small\deformation regime (lambda less than or equal to 1.2), considerable reinforcement (a factor of 10 in Young's modulus with respect to the pure nanolatex) is obtained with silica volume fractions of the order of 10%. At higher elongations, the reinforcement factor decreases, and the rheology of the nanocomposite samples approaches that of the pure nanolatex films.