Conditions for the Existence of a Stable Colloidal Liquid

In atomic and molecular systems the range and strength (inverse temperature) of the attraction is set by quantum mechanics. In many cases a Lennard-Jones potential describes the pair interaction quite well [7]. The phase behavior of atomic and molecular systems is often represented in a pressure versus temperature diagram. Quite often the distance between triple point (tp) and critical point (cp) is significant so that there is a wide region where a liquid exists the liquid window is then wide. 

Upon changing the range and strength of the attraction the distance between tp and cp changes. At a certain range and strength this distance reduces to zero then we reach the critical endpoint (cep), which constitutes the boundary condition for the existence of a stable liquid. The simplest case for which this can be illustrated is a 

Highlights in Colloid Science. Edited by Dime Platikanov and Dotchi Exerowa Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32037-0 

In this chapter we compare the predictions of these three models, Yuk, fix and var. We first present phase diagrams in terms of the strength and the range as a function of the colloid concentration in these three models. We find that the critical endpoint is essentially the same in the three cases the range in the cep is about one-third of the colloid radius, the strength is about 2kT. Outside the cep the three models behave quite differently. 

We then investigate how these results translate into p(T) diagrams. For the Yukawa system classical textbook diagrams are found, but for the polymer/colloid systems the behavior is slightly different, yet well understood. 

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