Geometry and kinetics determine the microstructure in arrested coalescence of Pickering emulsion droplets

Abstract

An important strategy to stabilize emulsions is to arrest coalescence of the constituent droplets with an opposing rheological force. Colloidal particles adsorbed on the surface of emulsion droplets in a Pickering emulsion become increasingly crowded during successive coalescence events because the combined surface area of coalescing droplets is less than that of the constituent droplets. Beyond a critical density, the particles form a rigid shell around the droplet and inhibit both relaxation of the droplet shape and further coalescence. The resulting droplets have a nonuniform distribution of curvature and, depending on the initial coverage, may incorporate a region with negative Gaussian curvature around the neck that bridges the two droplets. Here, we resolve the relative influence of the curvature and the kinetic process of arrest on the microstructure of the final state. Identifying the dimensionless ratio of the rate of area changeȦ to the diffusion constant D as a measure of the importance of kinetics in this system, we show that this depends on the extrinsic geometry of the surface as opposed to the static packings that depend solely on intrinsic geometry. arXiv:1903.00305v1 [cond-mat.soft]

Shape multistability in flexible tubular crystals through interactions of mobile dislocations

“…The feedback that we observe between surface deformations and in-surface defect dynamics suggests connections to be explored between this work and other topics of current interest in soft matter physics, including: the stabilization of non-spherical droplet shapes in Pickering emulsions by packings of colloidal particles, often as crystals with many defects [52]; motile disclinations in active matter on flexible, curved surfaces [53,54]; and complex out-of-plane deformations in nematic elastomers with imprinted defects [32,33,55]. We hope that our findings will spur experimental investigations of colloidal freestanding tubular crystals, mesoscale analogues to carbon nanotubes and microtubules, as a versatile platform for programmable, reconfigurable microwires with switchable mechanical and photonic response properties [56,57].…”

Shape multistability in flexible tubular crystals through interactions of mobile dislocations

“…The feedback that we observe between surface deformations and in-surface defect dynamics suggests connections to be explored between this work and other topics of current interest in soft matter physics, including the stabilization of nonspherical droplet shapes in Pickering emulsions by packings of colloidal particles, often as crystals with many defects (83); motile disclinations in active matter on flexible, curved surfaces (84,85); and complex out-of-plane deformations in nematic elastomers with imprinted defects (38,39,86). We hope that our findings will spur experimental investigations of colloidal freestanding tubular crystals, which are mesoscale analogs to carbon nanotubes and MTs, as a versatile platform for programmable, reconfigurable microwires with switchable mechanical and photonic response properties (87,88).…”

Elongation and percolation of defect motifs in anisotropic packing problems

“…If overlaps cannot be removed, the algorithm backtracks and reduces the rate of reduction; the algorithm is halted when the reduction rate reaches a critical threshold. Details of this algorithm are presented in previous work [24,32,33] and necessary modifications to deal with anisotropic particles described in Methods below. For the Thomson problem, all charges are initially set equal and a minimum is found by conjugate gradient descent; a fraction χ = 1 2 of charges are randomly selected and increased in magnitude; then the energy is reminimized.…”