Synergistic Interaction in Emulsions Stabilized by a Mixture of Silica Nanoparticles and Cationic Surfactant

Abstract

Using a range of complementary experiments, a detailed investigation into the behavior of dodecane-water emulsions stabilized by a mixture of silica nanoparticles and pure cationic surfactant has been made. Both emulsifiers prefer to stabilize o/w emulsions. At high pH, particles are ineffective emulsifiers, whereas surfactant-stabilized emulsions become increasingly stable to coalescence with concentration. In mixtures, no emulsion phase inversion occurs although synergism between the emulsifiers leads to enhanced stability at either fixed surfactant concentration or fixed particle concentration. Emulsions are most stable under conditions where particles have negligible charge and are most flocculated. Freeze fracture scanning electron microscopy confirms the presence of particle flocs at drop interfaces. At low pH, particles and surfactant are good emulsifiers alone. Synergism is also displayed in these mixtures, with the extent of creaming being minimum when particles are most flocculated. Experiments have been undertaken in order to offer an explanation for the latter synergy. By determining the adsorption isotherm of surfactant on particles in water, we show that surfactant addition initially leads to particle flocculation followed by re-dispersion. Using suitable contact angle measurements at oil-water-solid interfaces, we show that silica surfaces initially become increasingly hydrophobic upon surfactant addition, as well as surfactant adsorption lowering the oil-water interfacial tension. A competition exists between the influence of surfactant on the contact angle and the tension in the attachment energy of a particle to the interface.

Continuous Fabrication of Hierarchical and Asymmetric Bijel Microparticles, Fibers, and Membranes by Solvent Transfer‐Induced Phase Separation (STRIPS)

“…CTAB aids nanoparticle dispersion in the ternary mixture and, more importantly, renders the nanoparticles partially hydrophobic via electrostatic adsorption ( Figure 1 a). [ 23 ] During STRIPS, CTAB diffuses to the external water phase due to the concentration gradient (the concentrations of CTAB in the ternary mixture and the external aqueous phase are >20 × 10 −3 M and 1 × 10 −3 M , respectively); however, since the concentration of CTAB in the ternary phase is very large, we do not expect this mass transfer to signifi cantly impact the effi cacy of CTAB in making the nanoparticles hydrophobic. This strategy of in situ surface modifi cation affords fl exibility in the selection of colloids lacking in the traditional bijel fabrication route.…”

Preparation of Double Emulsions using Hybrid Polymer/Silica Particles: New Pickering Emulsifiers with Adjustable Surface Wettability

“…One common approach here is surface derivatization with various commercially-available alkylsilanes. 20 However, similar results can be achieved simply by physical adsorption: recent literature examples include the adsorption of small molecule aromatic acids 21 or surfactants 22,23,24,25,26 onto silica nanoparticles.…”

Influence of Surfactant Concentration in the Emulsions on the Process of Oleophilic/Hydrophobic Porous Medium Imbibition

“…This explains a great deal of the results regarding the influence of different emulsifiers on emulsions stability, and their mechanical and morphological properties, e.g. size distribution of droplets, their shape, dispersity, and others [12]- [15], [20]- [22].…”