Interaction Between Silica Nanoparticles and Cationic Surfactants and Thereby Induced Double Phase Inversion of n-Octane-water Emulsions

Abstract

Abstract: Silica nanoparticles are not surface active due to their strong hydrophilicity. However, the negatively charged silica nanoparticles in aqueous media can be in situ surface activated by adsorbing cationic surfactant molecules and thereby aggregate to oil/water interface to stabilize emulsions. In this paper the in situ surface activation effects of three water soluble cationic surfactants of different structures, cetyltrimethylammonium bromide(CTAB) with single headgroup and single chain, didodecyldimethylammonium bromide(di-C12DMAB) with single headgroup and double chains, and trimethylene-di(tetradecacyloxyethyldimethyl ammonium bromide)(II-14-3), a Gemini cationic surfactant with double headgroups and double chains, were examined by characterizing the formation, stability and phase inversion of n-octane-water emulsions, and the relative mechanisms were explored by measuring zeta potentials, adsorption isotherms, and contact angles etc. The results show that a monolayer formation at particle/water interface with hydrophobic tail toward water, which transits the wettability of the particle from strongly hydrophilic to partially hydrophilic and partially hydrophobic, is responsible for the in situ surface activation. By adsorbing CTAB or II-14-3 the hydrophobicity of particles is appropriately enhanced so that they can stabilize n-octane-in-water[O/W(1)] emulsion, whereas by adsorbing di-C12DMAB a much denser monolayer can be formed which endows particles a hydrophobicity so strong that the O/W(1) emulsion can be inverted to W/O type. At high surfactant concentration double layer adsorption occurs at particle-water interface and particles are returned to hydrophilic and thus lose their surface activity, while the free surfactant concentration in aqueous phase is high enough to stabilize O/W(2) emulsion solely. Thus an O/W(1)→W/O→O/W(2) double phase inversion can be induced by simply increasing surfactant concentration for the emulsion stabilized by a mixture of silica nanoparticles and di-C12DMAB.

Key words: Silica nanoparticle, In situ surface activation, Cationic surfactant, Emulsion, Phase inversion

TrendMD:

CHEN Zhao, CUI Chen-Fang, CUI Zheng-Gang*. Interaction Between Silica Nanoparticles and Cationic Surfactants and Thereby Induced Double Phase Inversion of n-Octane-water Emulsions[J]. Chem. J. Chinese Universities, 2010, 31(11): 2246.

References

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