Dipolar fluids in simple matrices

The simplest disordered medium is realized by a matrix consisting of positionally quenched hard spheres. In this case, both the matrix matrix and the resulting fluid matrix interaction are given by Eq. (7.43). For simplicity we assume that matrix and fluid particles have the same diameter. 

The influence of the IIS matrix on the phase behavior of an adsorbed Stockmayer fluid is checked most easily by investigation of the stability limits (spinodals) of the Isotropic high-temperature phase. Indeed, localization of true phase coexistence Hues is significantly more difficult because of the lack of a closed expression for the pressure within the replica HNC approach. 

These considerations motivated us to focus mainly on the dilute matrix case in what follows. In particular, one observes from Fig. 7.2 that the (gas Hquid) critical point of this system is displaced toward lower temperature and lower density where the latter shift essentially disappears if additional attractions between fluid particles and the matrix are included in the model [310]. 

These trends are similar to what is observed in simpler model fluids with purely spherically s3mimotric interactions [298, 313], which is to some extent expected because the gas liquid transition in Stockmayer fluids is mainly driven by the isotropic LJ (12,6) interactions underlying this model. We show in Ref. 307 that the main effects of HS matrices on the condensation can be reproduced when the dipolar model fluid is approximated by a fluid with angle-averaged dipolar interactions that are not only spherically symmetric but also short-ranged (they decay in proportion to for r — cx)). This notion is particularly important for future simulation studies on adsorbed dipolar fluids. 

At high fluid densities, bulk Stockmayer fluids exhibit an IF transition, which is signaled by a divergence of the dielectric constant eo [see Eq. (7.30)]. Results for cq are displayed in Fig. 7.3, which suggests that the IF transition 

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