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2D “Soap”-Assembly of Nanoparticles via Colloid-Induced Condensation of Mixed Langmuir Monolayers of Fatty Surfactants

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journal contribution
posted on 10.01.2012, 00:00 by Denis I. Babenko, Alexander A. Ezhov, Dmitry S. Turygin, Vladimir K. Ivanov, Vladimir V. Arslanov, Maria A. Kalinina
We describe a new type of colloidal 2D gels formed in mixed Langmuir monolayers of stearic acid and octadecylamine on a surface of gold hydrosol. The adsorption of gold nanoparticles on the mixed monolayer led to an increase of interactions between oppositely charged surfactants giving a “soap” of mixed fatty salt. The observed effect is equivalent to a virtual “cooling” of floating monolayer, which undergoes rapid condensation on a surface of aqueous colloid. The consequent shrinking and rearrangement of the monolayer resulted in aggregation of nanoparticles into colloidal 2D “soap”-gels, which represented arrested colloidal phases within nonadsorbing organic medium. When sequentially deposited onto solids by Langmuir–Blodgett technique, the 2D “soap”-gels separated into organic and colloidal phases and gave dendrite-like bilateral organic crystallites coated with gold nanoparticles. The reported colloidal “soap”-assembly can offer a new opportunity to design 2D colloidal systems of widely variable chemistry and structures.