Equation of state of colloids coated by polyelectrolyte multilayers.

We propose an adaptation of the osmotic stress technique for determining equations of state of colloids covered by polymer films. We describe here the case of silica particles covered by 6 or 7 layers of polyelectrolyte multilayers. The establishment of a pressure-distance curve allows the interpretation of colloidal interactions over more than four orders of magnitude in pressure. This large range allows a clear separation between three distinct regimes: layer compression, brush extension and at very low pressures a regime of weak repulsion. The physical origins of the regimes are discussed and described by models of colloidal interactions.