Model nanocomposites based on laponite and poly(ethylene oxide): Preparation and rheology

This paper describes the preparation of model nanocomposites based on geometrically well-defined particles (laponite) dispersed into a PEO matrix of narrow molecular weight distribution. The preparation involves the protection of the laponite particles with an adsorbed or a grafted layer of PEO chains. The adsorption is carried out in solution and the particles are recovered with a freeze-drying process. The surface coverage can be controlled from this process to obtain either starved or saturated particles. The protected particles are dispersed into the PEO matrix in the molten state thanks to a microcompounder. The linear viscoelastic properties are studied in the molten state and analyzed in light of the state of dispersion of the particles as determined by X-ray diffraction. The dispersion of the particles as individual entities is shown to increase with the surface coverage of the particles and grafted chains appear more efficient than adsorbed ones to achieve exfoliation. The formation of a gel is obtained above a critical volume fraction (on the order of 0.2-0.4% depending on the protection of the particles) where the elastic moduli increase with a power law of the frequency. The elastic modulus and the yield stress in the gel state increase with a power law of the particle's concentration with exponent 4.5 and 3.3 respectively, in agreement with a fractal arrangement of the particle's network in the matrix.