Synergistic stabilization of emulsions by a mixture of surface-active nanoparticles and surfactant

被引:258
作者
Binks, Bernard P. [1 ]
Desforges, Alexandre
Duff, Daniel G.
机构
[1] Univ Hull, Dept Chem, Surfactant & Colloid Grp, Kingston Upon Hull HU6 7RX, N Humberside, England
[2] Bayer Technol Serv GmbH, PT PDSP, D-51368 Leverkusen, Germany
关键词
D O I
10.1021/la062510y
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The stability and rheology of tricaprylin oil-in-water emulsions containing a mixture of surface-active hydrophilic silica nanoparticles and pure nonionic surfactant molecules are reported and compared with those of emulsions stabilized by each emulsifier alone. The importance of the preparation protocol is highlighted. Addition of particles to a surfactant-stabilized emulsion results in the appearance of a small population of large drops due to coalescence, possibly by bridging of adsorbed particles. Addition of surfactant to a particle-stabilized emulsion surprisingly led to increased coalescence too, although the resistance to creaming increased mainly due to an increase in viscosity. Simultaneous emulsification of particles and surfactant led to synergistic stabilization at intermediate concentrations of surfactant; emulsions completely stable to both creaming and coalescence exist at low overall emulsifier concentration. Using the adsorption isotherm of surfactant on particles and the viscosity and optical density of aqueous particle dispersions, we show that the most stable emulsions are formed from dispersions of flocculated, partially hydrophobic particles. From equilibrium contact angle and oil-water interfacial tension measurements, the calculated free energy of adsorption E of a silica particle to the oil-water interface passes through a maximum with respect to surfactant concentration, in line with the emulsion stability optimum. This results from a competition between the influence of particle hydrophobicity and interfacial tension on the magnitude of E.
引用
收藏
页码:1098 / 1106
页数:9
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