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Issue 45, 2012
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Nanoscale structure of surfactant-induced nanoparticle monolayers at the oil–water interface

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Abstract

Water-dispersed silica nanoparticles (NPs) do not adsorb to the interface between immiscible bulks of water and hexane. Adding, however, a surfactant (cetyltrimethylammonium bromide, CTAB) to water induces the formation of a NP monolayer (ML) at this model liquid–liquid interface. We determined the ML's structure in situ at deeply buried planar waterhexane interfaces with sub-nanometer resolution by high energy X-ray reflectivity. Detailed modeling of the data yields the NPs' interfacial concentration and water immersion depth, allowing calculation of the NP average contact angle Θ. At a CTAB concentration ϕc = 0.75 mM, comparable to the critical micelle concentration, a dilute NP monolayer is found with Θ ∼ 128°. At lower surfactant concentration (ϕc = 0.05 mM) we find a dense ML of close-packed NPs with an unexpectedly high Θ ∼ 146°. The structure and adsorption scenarios of the NPs at the interface are discussed, highlighting the relevance of the present method for quantitative studies of a broad range of systems and applications.

Graphical abstract: Nanoscale structure of surfactant-induced nanoparticle monolayers at the oil–water interface

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Publication details

The article was received on 30 Jun 2012, accepted on 20 Aug 2012 and first published on 20 Sep 2012


Article type: Paper
DOI: 10.1039/C2SM26520F
Citation: Soft Matter, 2012,8, 11478-11483
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    Nanoscale structure of surfactant-induced nanoparticle monolayers at the oil–water interface

    D. C. E. Calzolari, D. Pontoni, M. Deutsch, H. Reichert and J. Daillant, Soft Matter, 2012, 8, 11478
    DOI: 10.1039/C2SM26520F

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