Casimir amplitudes and capillary condensation of near-critical fluids between parallel plates: Renormalized local functional theory

摘要

We investigate the critical behavior of a near-critical fluid confinedbetween two parallel plates in contact with a reservoir by calculating theorder parameter profile and the Casimir amplitudes (for the force density andfor the grand potential). Our results are applicable to one-component fluidsand binary mixtures. We assume that the walls absorb one of the fluidcomponents selectively for binary mixtures. We propose a renormalized localfunctional theory accounting for the fluctuation effects. Analysis is performedin the plane of the temperature T and the order parameter in the reservoir\psi_{\infty} . Our theory is universal if the physical quantities are scaledappropriately. If the component favored by the walls is slightly poor in thereservoir, there appears a line of first-order phase transition of capillarycondensation outside the bulk coexistence curve. The excess adsorp- tionchanges discontinuously between condensed and noncondensed states at thetransition. With increasing T, the transition line ends at a capillary criticalpoint T = T_c^{ca} slightly lower than the bulk critical temperature T_c. TheCasimir amplitudes are larger than their critical-point values by 10-100 timesbetween the transition line and the bulk coexistence curve and slightly abovethe capillary critical point.