Adsorption of Anionic and Cationic Surfactants on Anionic Colloids: Supercharging and Destabilization

Abstract

We present herein a study on the adsorption of anionic (SDS), cationic (CTAB), and nonionic (C(12)E(5)) surfactants onto anionic silica nanoparticles. The effects of this adsorption are studied by means of the static structure factor, S(q), and the collective diffusion coefficient, D(c), obtained from small-angle X-ray scattering and dynamic light scattering measurements, respectively. The effective charge on the particles was determined also from classical electrophoresis and electroacoustic sonic-amplitude measurements. The surface tension of the sample was also investigated. Of particular note is the adsorption of SDS onto the silica nanoparticles, which leads to supercharging of the interface. This has interesting repercussions for structures obtained by the layer-by-layer (LbL) technique, because emulsions stabilized with supercharged and hydrophobized silica are perfect candidates for use in a multilayer system.

Effects of silica-based nanostructures with raspberry-like morphology and surfactant on the interfacial behavior of light, medium, and heavy crude oils at oil-aqueous interfaces

“…The SiO 2 NPs that are surrounded by large amounts of surfactant act as a carrier of the nonionic surfactant Tween Ò 20 which migrates toward the interface of the oilaqueous systems. Consequently, the reduction in IFT is the possible result of a surfactant release from the particles at the interface and an alteration in tension (Ahualli et al 2011). Further, the precipitous decline in the dynamic IFT may be a result of the physical properties of SiO 2 NPs (e.g., the size) rather than the interaction between SiO 2 NPs and surfactant.…”

“…It is possible that the observed IFTs are a result of either (1) the depletion of surfactant solution from the adsorption of Tween Ò 20 on the particle, which thus causes an increase in IFT with an increase in nanoparticle concentration, or (2) the adsorption of NPs at the interfacial layer, which decreases the IFT (Ravera et al 2006(Ravera et al , 2008. In the absence of surfactant or at low surfactant concentrations, SiO 2 NPs are fully wetted in the aqueous phase and remain within the bulk solution, avoiding the interface (Ravera et al 2006(Ravera et al , 2008Ahualli et al 2011). However, the subsequent increase in the nonionic surfactant concentration results in a corresponding increase in the number of SiO 2 NPs at the interface (Ravera et al 2006(Ravera et al , 2008.…”

“…SiO 2 NPs that are bonded to surfactant on their surface can operate as carriers of Tween Ò 20 toward the interface. The decrease in IFT may be attributed to surfactant release from the SiO 2 NPs or the direct effect of surfactant-coated SiO 2 NPs on the IFT (Ahualli et al 2011).…”

Adsorption of an anionic surfactant at air-liquid and different solid-liquid interfaces from solutions containing high counter-ion concentration

“…Despite that the ALA surface carries negative charge, SDBS adsorption at the ALA-liquid interface is significant (even higher than its adsorption on the neutral hydrophilic surface, BME). There are a number of studies [4,32,35,[40][41][42][43][44][45][46] reporting significant adsorption of ionic surfactants on similarly charged surfaces; among which anionic surfactant adsorption onto silica surfaces (negatively charged) has been widely reported in the literature [35,40,41,46,47]. Unlike the case of surfactant adsorption on oppositely charged surfaces, the adsorption on surfaces carrying similar charge to that on the surfactant molecules is not electrostatically driven [35].…”

Surfactant Adsorption and Aggregate Structure at Silica Nanoparticles

“…Surfactant adsorption onto hydrophilic surfaces can be regarded as a surface aggregation process, reminiscent of micelle formation in solution [6][7][8][9][10][11][12][13][14]. When the anchoring of the surfactant heads to the surface is weak, as in the case of nonionic surfactants at oxide surfaces, the morphology of surface aggregates may depend both on the anchoring strength [15,16] and on the curvature of the adsorbing surface [17][18][19][20][21][22][23]. For instance, for the surfactant penta (ethyleneglycol) monododecylether (C 12 E 5 ) it was recently found that discrete surface micelles are formed on silica nanoparticles [19,21], although flat bilayers aggregates are preferred at planar silica surfaces [11,12].…”