Pickering water-in-water emulsions: A review on their rheological and tribological performance

Pickering water-in-water (W/W) emulsions have attracted renewed research attention owing to the recent discovery of their aqueous lubrication performance. We cover the current knowledge of Pickering W/W emulsions regarding their rheological and tribological performance. Particularly, we examine the recent advances that have surfaced in the literature in the last five years, highlighting how the two phases and the Pickering particles affect the rheological properties and microstructural evolution of W/W emulsions when subjected to various degrees of shear stresses. We postulate how biolubrication performance of Pickering W/W emulsions can be altered by formulation engineering of the water droplets to offer fluid film lubrication while the particles providing boundary lubrication. This review therefore offers a stepping stone in highlighting the requirement of systematic experimental studies and rational design of the next-generation Pickering W/W emulsions for them to act as effective aqueous lubricants for a range of biomedical and allied applications.