5 - Particle-Laden Interfaces: Rheology, Coalescence, Adhesion and Buckling

Summary

Introduction

Particulate additives are found in the formulations of a great many high-surface area products in the form of emulsions and foams. Their presence is normally desirable for the purposes of stability. In the case of ice cream foams, tiny fat globules can attach themselves to the surfaces of the air pockets and hinder the process of coarsening by Ostwald ripening. In this case, the particles are a natural ingredient. In other instances, colloidal particles are deliberately added and Pickering emulsions are an important example. The occurrence of particles leading to stabilization can also be unwelcome, as in the case of emulsions formed when seawater and crude oils vigorously mix. This environmental problem can lead to very stable emulsions as a result of particles formed by asphaltenes or clay collecting at the oil–water interface.

The presence of particles at a fluid–fluid interface leads to numerous, profound consequences. Since a very large amount of energy is normally required to remove a particle from an interface (see Chapter 1 for a detailed explanation of this point), particles in these monolayers are normally irreversibly attached. Furthermore, as described in Chapter 2, these systems can be modified by exquisite tuning of interparticle forces, particle chemistry and particle size to create a wide range of morphologies of these “2-D suspensions”.