Elasticity of Interfacial Rafts of Hard Particles with Soft Shells

TL;DR

This paper develops an elasticity model for particle monolayers with hard cores and soft shells at liquid interfaces, revealing unique buckling and shape behaviors distinct from traditional elastic models.

Contribution

It introduces a continuum elasticity theory for hard-core/soft-shell particle rafts, providing new insights into their buckling and shape characteristics.

Findings

Hard cores induce capsule wrinkling during buckling.

Apparent elastic moduli can be significantly higher than actual values.

Shape analysis reveals differences from Hookean elasticity models.

Abstract

We study an elasticity model for compressed protein monolayers or particle rafts at a liquid interface. Based on the microscopic view of hard-core particles with soft shells, a bead-spring model is formulated and analyzed in terms of continuum elasticity theory. The theory can be applied, for example, to hydrophobin-coated air-water interfaces or, more generally, to liquid interfaces coated with an adsorbed monolayer of interacting hard-core particles. We derive constitutive relations for such particle rafts and describe the buckling of compressed planar liquid interfaces as well as their apparent Poisson ratio. We also use the constitutive relations to obtain shape equations for pendant or buoyant capsules attached to a capillary, and to compute deflated shapes of such capsules. A comparison with capsules obeying the usual Hookean elasticity (without hard cores) reveals that the hard cores trigger capsule wrinkling. Furthermore, it is shown that a shape analysis of deflated capsules with hard-core/soft-shell elasticity gives apparent elastic moduli which can be much higher than the original values if Hookean elasticity is assumed.