Spontaneous Emulsification of Oil in Aerosol-OT/Water/Hydrocarbon Systems
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- 作者：Taisei Nishimi and Clarence A. Miller
- 刊名：Langmuir
- 出版年：2000
- 出版时间：November 28, 2000
- 年：2000
- 卷：16
- 期：24
- 页码：9233 - 9241
- 全文大小：450K
- 年卷期：v.16,no.24(November 28, 2000)
- ISSN：1520-5827
文摘
Drops containing a hydrocarbon, the anionic surfactant Aerosol-OT (AOT), and water were injected intowater at 30 
C, and the resulting behavior was observed by videomicroscopy. Spontaneous emulsificationof most of the injected oil yielding droplets a few microns in diameter was seen when n-octane was thehydrocarbon and when the initial drop contained at least 25 wt % AOT and no more than about 10 wt %water. Emulsification was also observed when the initial drop contained small amounts of NaCl solutioninstead of water and for suitable conditions when n-hexane was the hydrocarbon. However, much lessemulsification occurred for n-decane and n-dodecane, probably because surfactant-rich phases in equilibriumwith excess oil in these systems solubilized little hydrocarbon. The mechanism of emulsification is closelyrelated to that of an earlier study by Rang and Miller (Prog. Colloid Polym. Sci. 1998, 109, 101) using dropscontaining n-hexadecane, the pure nonionic surfactant C12E6, and n-octanol. In both systems diffusionproduced inversion from an oil-continuous to a water-continuous phase, leading to emulsification at locationswhere supersaturation in oil occurred. One difference in the present case was that inversion was notcontinuous but involved formation of the lamellar liquid crystalline phase. Another was that the shift tomore hydrophilic conditions leading to inversion was caused by decreases in ionic strength of water in theinjected drop which, in turn, was produced by diffusion of water into the drop and of AOT and, in somecases, NaCl out of the drop. Owing to this ionic strength effect, nearly complete emulsification to smalloil droplets was observed in some ternary AOT/hydrocarbon/water systems in the present study but wasnot possible in ternary nonionic surfactant/hydrocarbon/water systems investigated previously.
C, and the resulting behavior was observed by videomicroscopy. Spontaneous emulsificationof most of the injected oil yielding droplets a few microns in diameter was seen when n-octane was thehydrocarbon and when the initial drop contained at least 25 wt % AOT and no more than about 10 wt %water. Emulsification was also observed when the initial drop contained small amounts of NaCl solutioninstead of water and for suitable conditions when n-hexane was the hydrocarbon. However, much lessemulsification occurred for n-decane and n-dodecane, probably because surfactant-rich phases in equilibriumwith excess oil in these systems solubilized little hydrocarbon. The mechanism of emulsification is closelyrelated to that of an earlier study by Rang and Miller (Prog. Colloid Polym. Sci. 1998, 109, 101) using dropscontaining n-hexadecane, the pure nonionic surfactant C12E6, and n-octanol. In both systems diffusionproduced inversion from an oil-continuous to a water-continuous phase, leading to emulsification at locationswhere supersaturation in oil occurred. One difference in the present case was that inversion was notcontinuous but involved formation of the lamellar liquid crystalline phase. Another was that the shift tomore hydrophilic conditions leading to inversion was caused by decreases in ionic strength of water in theinjected drop which, in turn, was produced by diffusion of water into the drop and of AOT and, in somecases, NaCl out of the drop. Owing to this ionic strength effect, nearly complete emulsification to smalloil droplets was observed in some ternary AOT/hydrocarbon/water systems in the present study but wasnot possible in ternary nonionic surfactant/hydrocarbon/water systems investigated previously.