Spreading behavior of oil-in-water emulsion on model solid substrates

Abstract

In this report, we have studied the spreading behavior of cosmetic oils along with sunscreen on PMMA and Teflon. It was observed that most of the cosmetic oils used, spread completely on PMMA where as on Teflon it makes certain contact angle. Based on the spreading experiments, we found through Zisman plot that critical surface tension of Teflon is ~21 mN/m. We found anomaly in spreading, in case of mixture of IPM and MCX and based on our finding, we concluded that not only surface tension but also viscosity of oil plays important role in spreading phenomenon. We also measured the IFT of pure oils with and without nonionic surfactant and in case of pure oils, lower IFT value is observed when the interaction happens through hydrogen bond interaction and higher IFT values are obtained when the interactions are van der waals in nature. Nonionic surfactant, C12EO7 brings down the IFT values very significantly to ~0.5mN/m and we also measured the emulsion droplet size with various concentration of surfactant. It was observed that smaller droplet sizes were obtained at higher surfactant concentration. Spontaneous spreading of IPM emulsion with C12EO7 as surfactant on glass and Teflon was performed. It was observed that in case of glass, precursor film first moves where as emulsion droplets are not spreading further and they are pinned. After a period of time, emulsion droplet coalesces and spreads completely. In case of Teflon, we found that movement of precursor film was very slow and the distance travelled by the film was less compared to glass.