Deformation of the Water/Oil Interface during the Adsorption of Sterically Stabilized Particles

Abstract

The adsorption of sterically stabilized colloids at water/oil (w/o) interfaces is studied experimentally by the formation of Pickering emulsions. Specifically, the effect of the steric stabilizer with respect to the rate of particle adsorption is investigated. Uniform, micrometer-sized poly(methyl methacrylate) (pMMA) particles, which are sterically stabilized with poly(isobutylene) (pIB), are used. The pIB concentration on the particle surface (ΓPIB) is controlled during the synthesis by adjusting the pIB/monomer ratio. Pickering emulsions are formed directly by the addition of water to the nonaqueous pMMA dispersions and subsequent emulsification. A strong dependence of the rate of particle adsorption on ΓPIB is found. The rate constant k for particle adsorption decays exponentially with ΓPIB, which suggest the use of a Boltzmann factor to model the experimentally found rate constants. The experimental results can be explained when the activation barrier for particle adsorption EA is of the same order as the average kinetic energy EK of a particle colliding with an emulsion droplet, which is equivalent to 10(5) kBT. Interestingly, this makes EA several orders of magnitude greater than the steric interaction with another particle. A possible mechanism that can lead to such a significant repulsive force is the inhibited drainage of solvent between the particle and o/w interface. Deformation of the o/w interface then occurs, when the solvent does not have time to drain, which results in a dramatic increase in the interfacial energy. This study identified the relevance of drainage in the formation of Pickering emulsions.

Stabilization of Pickering Emulsions by Hairy Nanoparticles Bearing Polyanions

“…Thus, when the ultrasonication time was 1 min, a floating oil layer existed with unstable emulsion. The ultrasonication energy from the extra 2 min was convenient and facilitated the formation of Pickering emulsions, at the same time droplets size was getting smaller, which was also observed in the previous report [35]. It was concluded that in order to stabilize the droplets, more particles were absorbed to the W/O interface with shear time.…”

Recent Studies of Pickering Emulsions: Particles Make the Difference

“…Other studies also showed that the electrostatic force would affect the adsorption of particles at the oil‐water interface, the assembly separation of particles on the interface, and the stability of the formed Pickering emulsions . Klumperman et al studied the effect of the surface concentration of graft on the stability of Pickering emulsions . They established a theoretical model and calculated a suitable surface concentration of graft for particles to achieve both the partial wetting and colloidal stability that are necessary for preparing stable Pickering emulsions.…”

Surface Wettability-Switchable Janus Fiber Fragments Stabilize Pickering Emulsions for Effective Oil/Water Separation

“…The results showed that the hydrophilic chains had an optimal length to keep Pickering emulsion stable. A short molecular chain could not provide sufficient steric hindrance against emulsion aggregation, while a long molecular chain with more hydrogen bonds had a higher activation energy in the continuous phase . Thus, PNIPAm of 2200 Da could effectively avoid the oil–water separation that occurred in the demulsification and was more suitable for oil–water separation.…”