Influence of Interfacial Rheological Properties on the Stability of Pickering Foams

Abstract

This work is aimed at gaining a fundamental understanding of the role of interfacial phenomena in foam stability. We have investigated the properties of Pickering foams, stabilized with fumed and spherical colloidal silica nanoparticles, and studied the impacts of particle attributes on the resulting properties such as bubble microstructure, foam liquid content, and foam half – life. We have examined the microstructure of analogue particle – laden interfaces and probed their response to applied deformations via both interfacial dilatational and shear rheology measurements. While the overall foam heights and microstructure remain similar for both particle types used, differences are observed in their interfacial shear and dilatational rheological measurements. Foams stabilized with fumed silica particles are able to resist liquid drainage to a higher degree, as captured by a plateaued reduced osmotic pressure over time, whereas the reduced osmotic pressure for the spherical particle – stabilized foams increased slowly over time. With regards to rheology, the interfacial network formed by spherical silica particle had slightly larger values of elastic moduli (𝐸’) than the fumed silica network. However, interfaces coated with fumed silica particles, undergoing dilational deformations, retained a particle network over a broader range of dilational strain compared to spherical particles. In shear mode, the interfacial networks formed by the spherical particles have higher storage moduli (𝐺’) compared to those obtained from fumed particles, whereas the critical shear strain corresponding to the yield point is larger for the fumed particle networks. Our findings demonstrate that while both fumed and spherical silica particles are able to stabilize the air/water interface and make long – lasting foams, the resulting Pickering foams are markedly different with respect to their network properties and resistance to various destabilization mechanisms.