Pickering Emulsions:  Interfacial Tension, Colloidal Layer Morphology, and Trapped-Particle Motion

Abstract

We have studied oil-in-water emulsions stabilized by monodisperse, fluorescent silica colloids presenting either a smooth or a rough surface. The presence of the fluorescent core allows for direct visualization of the colloids on the surface of the emulsion droplets. Droplet interfacial tension, measured by micropipet tensiometry, is not modified by particle adsorption at the interface, suggesting a purely steric stabilization mechanism. Surface roughness is shown to considerably lessen the ability of particles to stabilize droplets. At variance with what is commonly assumed, no straightforward relation exists between the extent of particle interfacial adsorption and emulsion macroscopic stability; stable emulsions can be obtained even with very low droplet surface coverage. Finally, we directly monitor the Brownian motion of the adsorbed particles, showing that their surface diffusion coefficient is very close to the bulk value. Evidence of a possible role of particle surface dynamics on the stabilization of poorly covered droplets is presented.

Effective surface-shear viscosity of an incompressible particle-laden fluid interface

“…Examples of static effective properties of particle-laden fluid interfaces are surface tension [5], bending [6], and saddle-splay [7] elastic moduli. Dynamic properties include, in particular, surface rheological parameters [4].…”

Spatial Distribution of Nanocrystals Imaged at the Liquid-Air Interface

“…Adsorption of colloidal particles at liquid interfaces is a versatile way to control the stability of emulsion droplets or microbubbles [1][2][3][4] or to guide the self-assembly of colloidal particles into superlattices or membranes [5][6][7]. For particles of only a few nanometers in size, adsorption to the liquid-gas or liquid-liquid interface can be of order k B T and reversible [8], as for molecular surfactants.…”

Evanescent-wave dynamic light scattering at an oil-water interface: Diffusion of interface-adsorbed colloids

“…Related investigations in the literature agree with an increased slowing down for smaller particles. Based on videomicroscopy on fluorescent rough silica particles of R ≈ 770 nm at an octanol-water interface, Vignati, Piazza, and Lockhart report no slowing down compared to bulk diffusion at low interface coverage and only a factor of 3 slowing down for an interfacial coverage as high as 50% [32]. Contrary findings of a slowing down by four orders of magnitude compared to the bulk diffusion of 4.6-nm-sized coated CdSe particles at a toluene-water interface determined by fluorescence photobleaching methods are reported by Lin et al [33].…”