Asakura-Oosawa mixture

The idea to coarse-grain the description of a system containing a very large number of polymer chains such that each chain is represented by a single effective particle dates back to the Asakura Oosawa model [189 191] of polymer colloid mixtures. In this model, the colloidal particles (e.g., cross-linked polystyrene spheres with radii in the size range 100 nm < < 1 /im) are represented as hard... 

In order to model experimental systems with short-range attractions, different models have been used. Spherically symmetric interaction potentials, such as the simple square well (SW) [22], or the Asakura Oosawa (AO) depletion potential [23], model the colloid-polymer mixture considering that the polymers are ideal [24]. However, due to the short range of these simple potentials, crystallization and fluid-fluid phase separations occur in the same region where gelation is expected, what makes more difficult the interpretation of the data. Therefore, strategies to avoid this equilibrium phase separation have been devised. 

The volume restriction effect as discussed in this paper was proposed several years ago by Asakura and Oosawa (12,13). Their theory accounted for the instability observed in mixtures of colloidal particles and free polymer molecules. Such mixed systems have been investigated experimentally for decades (14-16). However, the work of Asakura and Oosawa did not receive much attention until recently (17,18). A few years ago, Vrij (19) treated the volume restriction effect independently, and also observed phase separation in a microemulsion with added polymer. Recently, DeHek and Vrij (20) have reported phase separation in non-aqueous systems containing hydrophilic silica particles and polymer molecules. The results have been treated quite well in terms of a "hard-sphere-cavity" model. Sperry (21) has also used a hard-sphere approximation in a quantitative model for the volume restriction flocculation of latex by water-soluble polymers. 

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