OSMOTIC-PRESSURE AND VISCOELASTIC SHEAR MODULI OF CONCENTRATED EMULSIONS

We present an experimental study of the frequency omega dependence and volume fraction phi dependence of tile complex shear modulus G(omega ,phi) of monodisperse emulsions which have been concentrated by an osm otic pressure Pi. At a given phi, the elastic storage modulus G'(omega )=Re[G(omega)] exhibits a low-frequency plateau G'(p), dominating the dissipative loss modulus G''(omega)=Im[G(omega)] which exhibits a mi nimum. Above a critical packing fraction phi(c), we find that both Pi( phi) and G'(p)(phi) increase quasilinearly, scaling as (phi-phi(c))(mu ), where phi(c) approximate to phi(c)(rcp), the volume fraction of a r andom close packing of spheres, and mu is an exponent close to unity. To explain this result, we develop a model of disordered droplets whic h interact through an effective repulsive anharmonic potential, based on results obtained for a compressed droplet. A simulation based on th is model yields a calculated static shear modulus G and osmotic pressu re Pi that are in excellent agreement with the experimental values of G'(p) and Pi.