Surface-Induced Phase Separation of O/W Nano-Emulsion

The hydrophobic properties of substrates are known to affect wetting behavior of the deposited multiphase droplets. In this study, decomposition of O/W nano-emulsion droplets placed onto various wettable surfaces with controlled hydrophobicity is investigated. It was found that thin film spreading of the oil phase over the substrate surfaces is one of the primary reasons for emulsion decomposition. Our data shows that decomposition occurs first near the droplet pole and not at the contact line. Various techniques (phase contrast optical microscopy, gravimetric measurements and Raman spectroscopy) have been used to reveal the mechanism of the emulsion destabilization. It was found that process of nano-emulsion decomposition on highly hydrophobic surfaces can be described as two-stage process with critical point at which the value of dynamic contact angle is suddenly increased. We propose a simple mass balance model to explain observed phenomena.