Ideal wet two-dimensional foams and emulsions with finite contact angle.

S J Cox,S Hutzler,D Weaire,A M Kraynik

doi:10.1039/c8sm00739j

Abstract

We present simulations that show that the equilibrium structure of an ideal two-dimensional foam with a finite contact angle develops an inhomogeneity for high liquid fraction φ. In liquid-liquid emulsions this inhomogeneity is known as flocculation. In the case of an ordered foam this requires a perturbation, but in a disordered foam inhomogeneity grows steadily and spontaneously with φ, as demonstrated in our simulations performed with the Surface Evolver.

Highlights

In emulsions, the term flocculation refers to the clustering of droplets, leading to the formation of density inhomogeneities
In the present paper we address some basic consequences of introducing finite contact angles into the standard model of 2D foams, by analysing simulations carried out with the Surface Evolver software of Ken Brakke.[10]
Unlike the familiar case of a foam with zero contact angle, an ideal two-dimensional foam with a finite contact angle develops an inhomogeneity for high liquid fraction f

Summary

Introduction

The term flocculation refers to the (spontaneous) clustering of droplets, leading to the formation of density inhomogeneities. We describe the onset of flocculation in computer simulations of two-dimensional (2D) liquid foams A finite contact angle implies that the interfacial tension associated with the bubble–bubble interfaces is less than twice that associated with the Plateau borders (see Fig. 1b). For bubbles immersed in a liquid, the presence of finite contact angles entails net attractive forces between them (see Fig. 2) when they are only slightly compressed together This is similar to the attraction between droplets, when considering emulsions.[9]. Henry Princen introduced the concept of a contact angle between a thin liquid film and its adjacent Plateau border[11] and he established its physical significance in foams and emulsions by analysing 2D ordered (hexagonal) monodisperse structures,[7] which admit analytical solutions.

Ordered hexagonal foams

Disordered foams with finite contact angle

Summary and conclusions

Conflicts of interest