Structuring of Nanoparticles Confined Between a Silica Microsphere and an Air Bubble

Abstract

This chapter contributes to the understanding of effects of confining surface deformability on the interaction within thin liquid films of colloidal nanoparticles. The influence of surfactant on the surface deformability and then on the structuring of the nanoparticles is investigated. The oscillatory force caused by the layering of the nanoparticles is detected between the AFM microsphere probe and an air bubble, and the oscillatory wavelength that reflects the interlayer distance of the nanoparticles is found to scale with colloidal nanoparticle concentration as $\phi ^{-1/3}$. Under constant experimental conditions (AFM probe radius, bubble size, Debye length and contact angle), the bubble stiffness is found to increase linearly with surface tension, while the oscillatory wavelength is not affected by the bubble deformability. In addition, cationic surfactant C$_{16}$ TAB display a different behavior on the retraction part of the force curve, in which a pronounced adhesion force is observed. This phenomenon might be attributed to the hydrophobic effect caused by the monolayer formation of cationic surfactant on the silica sphere surface. Thus a stable thin film of colloidal nanoparticles is assumed to be formed between the silica microsphere and the bubble when strong repulsive interaction exists.

Reproduced by permission of The Royal Society of Chemistry: Structuring of colloidal suspensions confined between a silica microsphere and an air bubble, Yan Zeng, Regine von Klitzing, Soft Matter, 2011, 7, 5329–5338.