Abstract
Surface-inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil-in-water emulsions. This is a result of attractive van der Waals forces between particles and oil droplets in water, which are sufficient to trap the particles in close proximity to oil-water interfaces when repulsive forces between particles and oil droplets are suppressed. The emulsifying efficiency of the highly hydrophilic particles is determined by van der Waals attraction between particle monolayer shells and oil droplets enclosed therein and is inversely proportional to the particle size, while their stabilizing efficiency is determined by van der Waals attraction between single particles and oil droplets, which is proportional to the particle size. This differentiation in mechanism between emulsification and stabilization will significantly advance our knowledge of emulsions, thus enabling better control and design of emulsion-based technologies in practice.
Highlights
Surface-inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil-in-water emulsions
Our results reveal that provided the electrical double layer (EDL) repulsion between the particles and oil droplets is suppressed, the van der Waals (VW) attraction between them is sufficiently strong to confine the particles in close proximity to oil droplet surfaces to form densely packed shells which efficaciously envelop the oil droplets for emulsion stabilization
Pickering emulsions stabilized by 200 nm silica particles with partially hydrophobized surfaces are sufficiently stable against the freeze-thaw action, since ∆E arising from the partial wetting of 200 nm particles (r=100 nm) with reasonably hydrophilic surfaces (θ=30°) at the oil-water interface is over 7000 kT (Figure 2b)
Summary
Surface-inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil-in-water emulsions. The VW emulsions are stabilized by small particles more effectively than by large ones, while the interchange of differently sized particles readily occurs between the surfaces of the dispersed oil droplets and the continuous water phase.
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