Simple fluids with competing short-range attractive and long-range repulsive (SALR) interactions are relevant in the study of many complex biological and soft matter systems. Our particular interest for this EPSRC funded project are ‘Synbio’ systems, where large stable clusters of a specific SALR-like solute are used as templates in the‘green manufacture’ of solid nanoparticles of silica and also magnetite.
Earlier work has already elucidated the low density equilibrium phase behaviour of SALR dispersions (M.B. Sweatman et.al., JCP 140, 124508(2014)). Cluster fluid and cluster solid phases were found above a‘critical cluster concentration’, or CCC. A first order cluster vapour to cluster liquid or solid phase was also predicted, and later the transition to the cluster solid phase proven to exist using simulations (M.B. Sweatman and L. Lue, JCP 144, 171102 (2016)).
This work goes one step further and extends our previous one-component SALR thermodynamic model to study the phase behaviour of binary mixtures where both fluid components interact through a hard core with short-range attractions (SA), but only one of the components exhibits an additional long-range repulsion (SALR). Mixtures of this kind are thought to be relevant to the Synbio manufacture process.
A key parameter is the cross-interaction strength between the SA/SALR fluids. A weak cross-interaction leads to behaviour that is a composite of the individual components, while for strong cross-interactions a very different qualitative behaviour is observed. In particular, when the cross-interaction is strong enough, equimolar clusters appear, regardless of whether the pure SA fluid is supercritical, or the pure SALR fluid would form clusters or not. These results will hopefully be useful for interpretation of experimental systems (Synbio or otherwise) where stable giant clusters are observed.
Advances in molecular simulation , Engineered self-assembly , Challenges and advances in fluid phase equilibria
