Structure and phase behavior of two-Yukawa fluids with competing interactions in planar slit pores

Abstract

A density functional perturbation theory, which is based both on the modified fundamental-measure theory and on the first-order mean-spherical approximation for long-range attractive and repulsive interactions, has been developed for studying the structure and phase behaviors of a competing system restricted to slit pores. The hysteresis loop for the adsorption and desorption curves indicates that the system exhibits vapor-cluster and cluster-liquid transitions which depend on the pair potential parameters and the slit width (H). The periodic spacing (D) of the cluster is commensurate with the periodicity of modulation in the particle density distribution and more closely related to the vapor-cluster and cluster-liquid phase transitions of the system. For the cluster phase, we find the transition from a single liquidlike slab to a multi-liquidlike slab with increasing the slit width. The multi-liquidlike slab is formed depending on the periodicity of modulation by finite-size artifacts. The cluster-related phase transitions, such as the vapor-cluster or cluster-liquid transitions occur for H>D, while for H<D the system only exhibits the vapor-liquid transition. At a low amplitude, the vapor-liquid transition disappears and the cluster-liquid transition only occurs for H<D. The coexistence curves for the confined phase diagram are contained within the corresponding bulk liquid-vapor coexistence curve. For a wide slit pore (H>D), the system exhibits two tricritical points, joined to one another by the line of second-order transition. The results support the conclusion that the confinement effect plays an important role in determining the equilibrium phase transition.

Microphase separations of the fluids with spherically symmetric competing interactions

“…10,15 (Throughout this work, we have fixed the pair potential parameters such as A = 0.5, z 1 = 1.0, and z 2 = 0.5 since it is difficult to calculate the topology of the phase diagram in the full space of A and ε). The chemical potential βμ = (1/V )[∂βF (ρ)/∂ρ] V .T has been calculated from the free energy, where V is the volume of the system.…”

“…The divergence of a structure factor at k = k c signals the transition from a disordered to an ordered cluster phase. 10,11,15 The locus of this line in the phase diagram is called the λ-line. For c (2) hs (k, ρ), we have used the analytic MFMT expression.…”

“…A few studies regarding the influence of confinement on the phase behavior of a competing system has been reported in the slit-type pore. 9,11,[13][14][15] More recently, Kim et al 15 had shown that the periodic spacing of the modulated structure is commensurate with the periodicity of modulation in the particle density distribution and the cluster phase only appears when the periodic spacing is greater than the slit width. Here, one of the important questions we consider is how the geometry of the pores, the size of the pores, and the competing interaction affect the structure and phase behaviors of a confined competing system.…”

“…The competing system is an interesting model, which has an attractive interaction at a short distance and a repulsive one at a long distance. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Such a competing system gives rise to various microphase separated phases including the cluster phases. Many studies have been made to understand microphase formations induced by the competing interactions in the bulk and confined phases.…”

“…However, the general behavior of a competing system under confinement has received very limited attention. 9,11,[13][14][15] In general, the confinement induces new pattern morphologies, which might not appear at all in the bulk. It also modifies the pattern morphologies by the geometrical symmetry of the pores.…”