A density functional approach is applied to study the adsorption of an associating model fluid in narrow cylindrical capillaries. The model with non-associative Lennard-Jones (LJ), attraction between fluid particles and the site-site association, permitting the formation of chains of LJ monomers, i.e. the two-site model for monomers, is investigated. The strength of associative interactions is varied in the model to obtain an insight into the role of the associative interactions on the phase diagrams of confined fluids. The fluid-pore walls interaction is chosen in the form of the Yukawa-type potential. The wetting properties of the confining solid surface is studied first. Next, we describe the first-order layering transitions in cylindrical pores and the phenomenon of capillary condensation in capillaries of molecular dimensions. We also analysed the structural changes in the adsorbed fluids accompanying layering transitions and capillary condensation. A comparison of the phase diagrams for the fluid in the cylindrical pores with two different radii and in the slit-like pores, with the same nominal width as the cylindrical pores, is performed. We have also compared the capillary evaporation phase diagram for the model in question in cylindrical and slit-like pores. The method and the results represent a useful basis for the development of inhomogeneous statistical associating fluid theory for several practical applications.

A density functional approach is used to study adsorption and phase behaviour of the two-bonding-site associating Lennard-Jones (LJ) fluid in slit-like pores with energetically heterogeneous walls. Phase behaviour of strongly and weakly associating, polymerizing fluid in the pores with a periodic surface potential, characterized by different strengths and the spacings between adjacent minima, as well as different pore widths is discussed. A comparison of the results obtained for strongly and weakly associating fluids elucidates the role of bonding between fluid species in the pore-filling mechanism. An interplay between layering transitions, the formation of an intermediate `bridge' phase and the final capillary condensation in the pores with energetically corrugated walls is discussed in detail.

We have studied the adsorption of associating fluids on solid substrates, in the framework of the models with two and four bonding sites and with nonassociative Lennard-Jones (LJ) attraction between fluid particles. The fluid-substrate interaction is chosen in the form of the 9-3 LJ-type potential. Our analysis involves the strongly adsorbing, graphitelike substrate, as well as several weaker model surfaces. Special attention is paid to the layering transitions, their relevance to the prewetting transition, and the prewetting transition on its own. We have evaluated the surface critical temperature and made estimates for the critical temperatures of the layering transitions and of the wetting temperature, for each model in question. An insight into thermodynamic behavior of the models is given in terms of the phase diagrams. Our calculations reveal that the details of the surface phase behavior of strongly associating fluids differ from the phase behavior for weakly associating fluids and of adsorbed, simple nonassociating fluid. Also, we have analyzed structural changes in the adsorbed films during transitions in question, considering the entire distribution of fluid particles and a set of distributions for fractions of differently bonded species.

No abstract

No abstract