Structuring of colloidal suspensions confined between a silica microsphere and an air bubble

Abstract

This study contributes to the understanding of the effects of confining surface properties on the interactions within thin liquid films of colloidal nanoparticles. Colloidal probe atomic force microscopy was used for studying the interaction of colloidal nanoparticles between the solid-liquid and air-liquid interfaces. The influence of the surfactant on the surface deformability and on the structuring of the nanoparticles was determined. Therefore, surfactants of different charges, i.e. sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (C 16 TAB) and b-dodecylmaltoside (b-C 12 G 2 ) were chosen. The oscillatory force caused by the layering formation of the nanoparticles was detected between the AFM microsphere probe and the bubble, and the oscillatory wavelength that reflected the interlayer distance of the nanoparticles was found to scale with colloidal nanoparticle concentration as c À1/3. Under constant experimental conditions (AFM probe radius, bubble size, Debye length and contact angle), the bubble stiffness was found to increase linearly with surface tension, while the oscillatory wavelength was not affected by the bubble's deformability. In addition, the cationic surfactant C 16 TAB displayed different behavior on the retraction part of the force curve, in which a pronounced adhesion force was observed. This phenomenon might be attributed to the hydrophobization caused by the monolayer formation of cationic surfactant on the silica sphere surface. Thus a stable thin film of colloidal nanoparticles was assumed to be formed between the silica microsphere and the bubble when electrostatic repulsion existed.

Oscillatory Forces of Nanoparticle Suspensions Confined between Rough Surfaces Modified with Polyelectrolytes via the Layer-by-Layer Technique

“…If there was an effect of surface elasticity, it was manifested as surface force curves that did not increase perpendicularly after the "contact point" but rather deviated from the straight line because of deformation of the surface. 55 This deviation was not observed in the present study even for the thickest film of 12 nm (PAH/ PSS, N = 10, at 0.1 M NaCl), indicating that the effect of surface elasticity was negligible.…”

“…Measurements between a rigid silica microsphere and a bubble reveal that the surface elasticity reduces the amplitude of oscillations. 55 In the present study, however, the thickness of the multilayer in the most cases was less than 6 nm; thus, the effect of surface elasticity was suppressed by the hard silica surface. If there was an effect of surface elasticity, it was manifested as surface force curves that did not increase perpendicularly after the "contact point" but rather deviated from the straight line because of deformation of the surface.…”

Depletion forces between particles immersed in nanofluids

“…The surface force apparatus (SFA) [62,63] and colloidal-probe AFM (CP-AFM) [52,53] gauge the forces with bending of a calibrated spring. Prominently, micelles [58,[64][65][66][67][68][69] and spherical nanoparticles (particularly SiO 2 [29,52,53,68,[70][71][72]) are among most widely studied model nanofluids for mediating depletion and related structural forces, with nanorods-mediated depletion also measured [60,61].…”

Effect of polyelectrolytes on (de)stability of liquid foam films

“…For Silica dispersions conned in a CP-AFM it has been shown that the structural forces (which corresponds to stratication in foam lms) are an effect of connement. The oscillation period is very robust against changes in elasticity of the surface (uid or solid), 79 surface charge, 80 surface roughness, 81 ionic strength 82 and against (non)presence of surfactants of different charges. 79 On the other hand, these parameters affect the amplitude (strength of ordering) and the decay length (range of ordering).…”