Direct Observation of Giant Pickering Emulsion and Colloidosome Droplet Interaction and Stability

Abstract

The interactions of two 2-mm pendant oil droplets grown in the presence of an aqueous solution of poly(glycerol monomethacrylate)-stabilized polystyrene latex particles was observed using a high-speed video camera. The coalescence behavior was monitored as a function of oil type (n-dodecane versus sunflower oil) and particle size (135 versus 902 nm), as well as in the presence and absence of an oil-soluble cross-linker [tolylene 2,4-diisocyanate-terminated poly(propylene glycol)]. The damping coefficient of the coalescing n-dodecane droplets was found to increase in the presence of the latex, demonstrating particle adsorption. Coalescence times increased when the oil phase was changed from n-dodecane to sunflower oil, because of the much higher viscosity of the latter oil. In addition, increasing the adsorbed particle size from 135 to 902 nm led to longer coalescence times because of the greater distance separating the oil droplets. Coalescence times observed in the presence of the larger 902-nm particles indicated that two different modes of contact can occur prior to a coalescence event (bilayer or bridging monolayer of particles in the film). Addition of an oil-soluble surface-active cross-linker to the sunflower oil phase to react with the hydroxy groups of the particle stabilizer reduced the interfacial elasticity and ultimately prevented coalescence after cross-linking for 20 min at 25 °C. Such giant colloidosomes can remain in contact for several hours without undergoing coalescence, which demonstrates their high stability. Furthermore, coalescence is prevented even if the cross-linker is present in only one of the pendant droplets. Finally, evidence for cross-linker diffusion from one pendant droplet to another was indicated by a visible filament connecting the two droplets upon retraction.

Colloidosomes: Synthesis, properties and applications

“…The coalescence behavior of similar covalently cross-linked colloidosomes 69,70 has been investigated using a high speed video camera. Initially, Thompson et al 70 observed that individual millimetre-sized Pickering emulsion droplets prepared using poly(glycerol monomethacrylate)-stabilized latex particles readily coalesced when brought into contact.…”

“…Initially, Thompson et al 70 observed that individual millimetre-sized Pickering emulsion droplets prepared using poly(glycerol monomethacrylate)-stabilized latex particles readily coalesced when brought into contact.…”

CHAPTER 9. Particle-Stabilized Emulsions as Templates for Hollow Spheres and Microcapsules

“…34 With this method, a range of particles has been used from sterically-stabilized latex, 30,31,35,36 microgel particles, 33 silica 37 or metallic nanoparticles and epoxy resin microrods. 38 For example, we have used polystyrene latex particles synthesized by emulsion polymerization in the presence of a diblock copolymer stabilizer, where the water-soluble block is pH-responsive.…”

Chapter 8. Multiple Pickering Emulsions for Functional Materials

“…[108][109][110][111][112][113][114][115][116][117][118][119][120][121][122][123][124] A hallmark of colloidosomes is their robust structure, as their building blocks are solid particles, which endow them with enhanced mechanical strength against coalescence. Another advantage associated with colloidosomes is that the permeability can be adjusted by changing the size of the particles.…”