Journal of Physical Chemistry, Vol.99, No.33, 12624-12630, 1995
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 types of systems. The solid particles were polystyrene with grafted methylpoly(ethylene oxide) of average 2000 molecular weight. This latex form stable suspensions. This latex was prepared by dispersion polymerization and produced particles with a radius of 315 nm and low polydispersity. 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 mixed by using low shear rates, and the theological properties of the mixtures were measured, as well as theological properties of the pure systems. 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, meaning that latex-latex, emulsion-emulsion, and latex-emulsion interactions are of the same type. In steady state measurements some dependence of phi(max) (maximum volume of packing) with volume fraction and shear rate was detected for the emulsion systems. This dependence shows the influence of the deformability of the droplets. At high volume fractions, the theological behaviors of the emulsion and the suspension are very different, in both steady state and dynamic measurements. The elastic modulus in the linear region depends on the volume fraction in an exponential fashion for solid particles while the dependence is linear for the deformable particles. The mixtures show intermediate behavior, and their elasticity is well represented by a simple model in which the emulsion and the suspension elastic modulus are used in series with the appropriate weights. A dependence of the critical strain (the strain above which the theological parameters start to depend on the strain) with volume fraction has been found. The critical strain decreases with volume fraction and goes to a minimum around phi(max).