Colloids dispersed in polymer solutions. A computer simulation study

Abstract

We report a computer-simulation study of a simple model for a colloid dispersed in a polymer solution. The simulations were performed using a computational scheme that allows simulation at constant osmotic pressure of the polymers. We present results for the polymer-induced interaction, the equation-of-state, and the phase diagram. The simulations show that when the radius of gyration of the polymers R, is sufficiently large compared to the diameter of the colloidal particles a,.,l (2 R,la,,,20.45), addition of polymer induces a colloidal "liquid-vapor" phase separation. For shorter polymers, only the solid-fluid transition is observed. In addition, we find that the nonpairwise additivity of the polymer-induced attraction between the colloidal particles has a pronounced effect on the equation-of-state and the phase behavior of a colloid-polymer mixture. The perturbation theory of Lekkerkerker et al. [Europhys. Lett. 20, 559 (1992)] is found to perform well, except at low densities.

Measurement of the Interfacial Tension of a Phase-Separated Colloid−Polymer Suspension

“…Phase transitions in colloid-polymer suspensions have attracted considerable attention, both theoretically and experimentally; see, for example, refs [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. It has become clear that for small polymer to colloid size ratios (<0.3) the transition is of the fluid-solid type, while for large size ratios (>0.3) three different phases can occur: two different fluid phases, i.e., a gaslike and a liquidlike phase, and one solid phase, a colloidal crystal.…”

Numerical Techniques to Study Complex Liquids

“…For more details, we refer the reader to ref. [49]. It turns out that the same approach can be used in other contexts.…”

“…In fact, it is shown in ref. [49], that for all but the shortest chain molecules, this non-additivity of the polymer-induced interaction between the colloids, has a pronounced effect on the structure and stability of the mixture. For more details, we refer the reader to ref.…”

“…From computer simulation [121,122,127,51,42] we know of many examples of de-mixing transitions in systems with purely hard-core interactions. Below, I discuss one particular class of de-mixing transitions in hard-core mixtures, namely depletion flocculation in colloids [128,49]. The reason why I discuss this example is that it allows me to introduce another technique to study phase transitions in complex fluids by computer simulation.…”

“…7 in a slightly different form: (7) dlnP AH = (8) dlIT PAVIT Examples of recent applications of the Kofke method can be found in refs. [48,49,50,51,47]. It should be stressed that the Kofke method is in no way limited to the computation of coexistence curves in the P,T plane.…”