Harnessing the advantages of hard and soft colloids by the use of core–shell particles as interfacial stabilizers

Abstract

The ability of colloidal particles to penetrate fluid interfaces is a crucial factor in the preparation of particle stabilized disperse systems such as foams and emulsions. For hard micron-sized particles the insertion into fluid interfaces requires substantial energy input, but soft particles are known to adsorb spontaneously. Particle hardness, however, may also affect foam and emulsion stability. The high compliance of soft particles may compromise their ability to withstand the lateral compression associated with disproportionation. Hence, particles which can spontaneously adsorb onto fluid interfaces, and yet depict low compliance may be ideal as interfacial stabilizers. In the present work, we prepared core-shell particles comprising a hard, polystyrene core and a soft poly(N-isopropylacrylamide) based shell. We found that such core-shell particles adsorb spontaneously onto various fluid interfaces. The absence of a pronounced energy barrier for interfacial adsorption allowed the facile preparation of particle-stabilized bubbles as well as emulsion droplets. For bubbles, the stability was better than that of bubbles stabilized by entirely soft particles, but disproportionation was not stopped completely. Emulsion droplets, in contrast, showed excellent stability against both coalescence and disproportionation. Lateral compression of core-shell particles due to disproportionation was clearly limited by the presence of the polystyrene core, leading to long-lasting stability. For emulsions, we even observed non-spherical droplets, indicating a negligible Laplace pressure. Our results indicate that core-shell particles comprising a hard core and a soft shell combine the advantageous properties of hard and soft particles, namely spontaneous adsorption and limited compliance, and can therefore be superior materials for the preparation of particle-stabilized dispersions.

Impacts of Size and Deformability of β-Lactoglobulin Microgels on the Colloidal Stability and Volatile Flavor Release of Microgel-Stabilized Emulsions

“…Particle stabilizers have a significantly greater desorption energy, and so the droplets had to adopt non-spherical shapes in order to reduce volume while maintaining the surface area taken up by the particles. A similar formation of non-spherical droplets has been observed in Pickering emulsions when forced to undergo partial coalescence [24] or when negative pressures were applied to the oil phase [16,25]. This can also occur for droplet interfaces saturated with strongly interactive biopolymers possessing signficant compression and shear elasticity [26].…”

Correlation between Physico-Chemical Characteristics of Particulated β-Lactoglobulin and Its Behavior at Air/Water and Oil/Water Interfaces

“…However, a crossing over of the curves may occur at longer time scales due to the less intense reduction in interfacial tension of the more cross-linked particles (109%) after the initial phase compared to the least cross-linked ones (85%). This could indicate a limited rearrangement at the interface due to the increased number of cross-links [ 41 , 43 ].…”

“…In this regard, it is important to mention that the smallest particles exhibited a much higher cross-linking degree (120%) compared to the larger ones (~105%). Thus, due to the enhanced ability of the less cross-linked particles to rearrange at the oil/water interface [ 43 ], a more pronounced reduction in interfacial tension was achieved.…”

Elastic deformation of soft coatings due to lubrication forces

“…In particular, there are no solutions for drainage past elastic coatings of finite thicknesses: coatings that do not fall within the limiting cases of an elastic foundation or a half-space. [14][15][16] More specifically, the unsteady case where a surface initially at rest moves toward a static one at a constant drive velocity is of particular importance in the measurement of dynamic surface forces and has yet to be investigated. 17,18 Finally, a cantilever spring needs to be incorporated to the model description to be applicable for surface forces measurements where the forces are measured via the deflection of a cantilever spring.…”