Spreading of emulsions on a solid substrate

The wettability of emulsions is a prominent factor with a broad impact on an extensive variety of industrial applications ranging from the petroleum to the cosmetic industries. Surprisingly, there is no comprehensive study of emulsion spreading to date. In this work, the spreading of water/silicone oil emulsions on glass substrates was investigated. The emulsions were prepared with varying volume fractions of water dispersed in silicone oil, with addition of small amounts of surfactant to stabilize the emulsion structure. The time-dependent variation of dynamic contact angle, base diameter, and the spreading rate of the emulsion droplets were studied. The effect of water/silicone oil weight percentage as well as the droplet size and dispersed phase bubble size were also investigated. The weight percentage of water/silicone oil emulsion and droplet size did not have a significant impact on the spreading dynamics; however, the dispersed phase bubble size affected the spreading dynamics substantially. The coarsening of the dispersed phase bubbles was the key factor in the distinct spreading behavior of emulsions compared to pure liquids.