INVESTIGATION OF THE INTERACTION BETWEEN EMULSIONS AND SUSPENSIONS (SUSPOEMULSIONS) USING VISCOELASTIC MEASUREMENTS

We studied mixtures of emulsion droplets and solid particles in order to determine the possibility of specific interaction between both type s of systems. The solid particles were polystyrene with grafted methyl poly(ethylene oxide) of average 2000 molecular weight. This latex form stable suspensions. This latex was prepared by dispersion polymerizat ion and produced particles with a radius of 315 nm and low polydispers ity. The emulsion was prepared by shearing a mixture of hexadecane and water and using a polymeric surfactant. Synperonic L92, as emulsifier . The Z-average droplet radius was 280 nm. Latex and emulsion were mix ed by using low shear rates, and the theological properties of the mix tures were measured, as well as theological properties of the pure sys tems. The oscillatory behaviors of the emulsion and the suspension are similar at low volume fractions, where the emulsion droplets seem to behave as hard spheres. No specific interaction could be detected, mea ning that latex-latex, emulsion-emulsion, and latex-emulsion interacti ons are of the same type. In steady state measurements some dependence of phi(max) (maximum volume of packing) with volume fraction and shea r rate was detected for the emulsion systems. This dependence shows th e influence of the deformability of the droplets. At high volume fract ions, the theological behaviors of the emulsion and the suspension are very different, in both steady state and dynamic measurements. The el astic modulus in the linear region depends on the volume fraction in a n exponential fashion for solid particles while the dependence is line ar for the deformable particles. The mixtures show intermediate behavi or, and their elasticity is well represented by a simple model in whic h the emulsion and the suspension elastic modulus are used in series w ith the appropriate weights. A dependence of the critical strain (the strain above which the theological parameters start to depend on the s train) with volume fraction has been found. The critical strain decrea ses with volume fraction and goes to a minimum around phi(max).