Near-critical confined fluids and Ising films: Density-matrix renormalization-group study - art. no. 056137

Two-dimensional Ising strips subject to identical surface fields h(1) = h(2 )greater than or equal to0 are studied for temperatures above and below the bulk critical temperature T-c and a range of bulk fields h by means of the density-matrix renormalization-group method. In the case of nonvanishing s urface fields, the near-critical behavior of the solvation force f(solv), t otal adsorption Gamma, inverse longitudinal correlation length xi (-1)(para llel to) and specific heat C-H is strongly influenced by the (pseudo) capil lary condensation that occurs below T-c. We obtain scaling functions of f(s olv), Gamma, and xi (-1)(parallel to). C-H exhibits a weakly rounded singul arity on crossing the pseudocoexistence line. We contrast these results wit h those for the case of free boundaries where. for temperatures slightly be low T-c, f(solv) and CH exhibit a sharp extremum away from h = 0. Our resul ts have direct repercussions for the properties of near-critical Ising film s in three dimensions and we argue that the long-ranged solvation (Casimir) force in confined fluids should be more attractive in the neighborhood of the capillary critical point than exactly at the bulk critical point.