Density functional theory integrated with renormalization group theory for criticality of nanoconfined fluids.

Nanoconfined fluids exhibit complicated behavior such as phase transitions, prewetting, wetting transitions, universal critical properties, and critical point shifts, attributed to the cooperative interactions of short- and long-range density fluctuations. In this work, a theoretical approach, an integrated density functional (DF) and renormalization group (RG) theory, is developed to investigate the critical properties of fluids confined in slit pores or bounded by single wall surfaces. The approach can take into account both the local and the long-range density fluctuations of confined fluids self-consistently. The predicted critical order parameter exponent beta is about 1/8, and the wetting exponent beta(s) is 1.056 +/- 0.011. These values are quite close to the two-dimensional Ising values, demonstrating that the new theoretical approach is reliable as a description of criticality in nanoconfined fluids. Correspondingly, the global phase transitions and surface wetting transitions are analyzed.