An emulsion is a liquid-in-liquid scenario so you need to frame your question differently. If you require a dispersion of ZnSt in water then a surfactant for wetting is required and stabilization either by charge (optimum concentration of phosphate here) or steric (with a polymer (PEG is mentioned above but a 50 kDa PEI has been found suitable in the past - again optimum concentration to cover the surface with a little to spare).