The effects of size and charge asymmetry on the gas-liquid critical parameters of a primitive model (PM) of ionic fluids are studied within the framework of the statistical field theory based on the collective variables method. Recently, this approach has enabled us to obtain the correct trends of the both critical parameters of the equisize charge-asymmetric PM without assuming ionic association. In this paper we focus on the general case of an asymmetric PM characterized by the two parameters: hard-sphere diameter-, $λ=σ_{+}/σ_{-}$ and charge, $z=q_{+}/|q_{-}|$, ratios of the two ionic species. We derive an explicit expression for the chemical potential conjugate to the order parameter which includes the effects of correlations up to the third order. Based on this expression we consider the three versions of PM: a monovalent size-asymmetric PM ($λ\neq 1$, $z=1$), an equisize charge-asymmetric PM ($λ=1$, $z\neq 1$) and a size- and charge-asymmetric PM ($λ\neq 1$, $z=2$). Similar to simulations, our theory predicts that the critical temperature and the critical density decrease with the increase of size asymmetry. Regarding the effects of charge asymmetry, we obtain the correct trend of the critical temperature with $z$, while the trend of the critical density obtained in this approximation is inconsistent with simulations, as well as with our previous results found in the higher-order approximation. We expect that the consideration of the higher-order correlations will lead to the correct trend of the critical density with charge asymmetry.
The Solvophobic Solvation and Interaction of Small Apolar Particles in Imidazolium-Based Ionic Liquids is Characterized by Enthalpy-/Entropy-Compensation
The moment sum-rules for ionic liquids at criticality
我们讨论了一般离子液体的前三个著名的矩电荷-电荷求和规则。对于限制原始模型的特殊对称情况，Das等人[Phys. Rev. Lett. 107，215701（2011）]最近通过蒙特卡罗模拟发现，Stillinger-Lovett或二阶矩求和规则在临界点失效。我们批判性地讨论了这种意外行为的可能解释。另一方面，四阶矩求和规则证明能够解释临界状态下的模拟结果。
