Rheological and interfacial properties of silicone oil emulsions prepared by polymer pre-adsorbed onto silica particles

Emulsions stabilized by colloidal particles, namely Pickering emulsions were prepared by mixing silicone oil with silica particles pre-adsorbed hydroxypropyl methyl cellulose (HPMC) in the continuous water phase as functions of added amount of HPMC and silicone oil viscosity. Characteristics of the resulting oil dispersed in water (O/W) emulsions were determined by the measurements of adsorbed amounts of the silica particles, oil droplet size, and some rheological responses, such as hysteresis loop, stress–strain sweep curve, and dynamic viscoelastic moduli. These results were compared with those prepared by silica particles without HPMC or HPMC. The adsorbed amounts of the silica particles pre-adsorbed HPMC were increased with an increase in the amount of added HPMC. However, no adsorption of the silica particles without pre-adsorbed HPMC occurred. The size of oil droplets prepared by the silica suspensions pre-adsorbed HPMC decreased with an increase in the adsorbed amount of HPMC and it increased with increasing the viscosity of the silicone oil at the fixed amount of adsorbed HPMC. The emulsions prepared by every emulsifier showed that their stress–strain sweep curves were satisfied with Hooke's law at the smaller deformation, whereas at the larger deformation they showed thixotropic behavior, irrespective of the silicone oil. An increase in the viscosity of the silicone oil gives the larger difference between the up and down curves at lower shear rates for the hysteresis loops. Moreover, dynamic viscoelastic moduli measurements showed that storage moduli of the emulsions were increased by one order of magnitude by adsorption of HPMC, where the elastic responses was controlled by the silica suspensions pre-adsorbed HPMC at the interface.