(349e) Controlling the Coalescence of Oil-Water Interfaces By Tuning the Structure of Core-Shell Colloidal Particles

Colloidal particles are used widely in fluid formulations to stabilize emulsions, known as Pickering emulsions. Polymer-grafted particles are common because the addition of polymer introduces both deformability and interfacial activity to the particles. In addition, polymers are sensitive to the solvent quality, so the length of polymer shell (in bulk and at the interface) can be tuned through the solvent quality via changing salt concentration or temperature. In this work, colloidal particles made of poly-N-isopropylacrylamide (pNIPAM) shell and silica core, are used as a model system to coat oil-water interfaces. These particles, having a swollen size of 600 nm, are found to be interfacially active and adsorb irreversibly to the interface. After the adsorption, concentrated sodium chloride solution is used to replace the bulk aqueous solution and collapse the pNIPAM shell of the adsorbed particles. There is little change in the interfacial properties of the coated interfaces, but there is an impact on drop-drop interaction. Coalescence experiments are performed before and after deswelling the polymeric shell and results show an order one effect on the coalescence behavior. This work provides insights on how colloidal structures at the interface change the stability of oil-water emulsions.