Introduction to Depletion Interaction and Colloidal Phase Behaviour

Abstract

Efforts to explain physical properties of colloidal suspensions in terms of the forces that act between the colloidal particles go back to the beginning of the 20th century. In the second half of the last century theoretical progress clarified that the stability of colloidal particles is also affected by non-adsorbing polymers in solution, as first explained by Asakura and Oosawa in Japan using the excluded and free volume concepts. Here an introduction to the depletion interaction and resulting phase behaviour in colloidal suspensions is provided. The theory for the phase behaviour of colloidal dispersions is developed here starting from the Van der Waals theory for the as-liquid phase transition. Subsequently, the hard sphere fluid-solid phase transition is explained. Next, an attractive Yukawa hard-core model is used to outline the effects of varying the range of attraction on the phase behaviour of a colloidal suspension of attractive particles. Finally, the phase states that can be found in a colloidal hard sphere dispersion plus depletants are explained.