Physical adsorption on patchwise heterogeneous surfaces. 3. Continuous phase transitions of krypton monolayers on (0001) graphite

Abstract

Experimental vapor pressure data for krypton adsorption on graphitized carbon black are analyzed thermodynamically such that the shapes of the thermodynamic singularities near phase transitions are preserved. The thermodynamic potential and all of its derivatives are calculated in the transition region. The analysis assumes a classical Ehrenfest type second-order transition for the "fluid-solid" monolayer transition. Singularities for this lower-density transition are much more pronounced in the compressibility and heat capacity at constant spreading pressure than in the isosteric heat or heat capacity at constant density. The higher-density phase transition region was investigated by careful differentiation of the experimental isotherms, which revealed a pronounced compressibility minimum at amount adsorbed = 124 ± 2 µ /g, and compressibility peaks at higher densities. The higher and lower-density peaks appear to all lie on a line of continuous order-disorder transitions, as in helium and nitrogen monolayers on graphite, and certain theoretical models.

Computer simulation of liquid-vapor coexistence of confined quantum fluids

“…(3) as the WK-1 model. Equation (3) agrees with the first-order expressions for V Q from Feynman-Hibbs, 62 Bohm's, 60 and Jaen-Khan theories. 36 In order to assess the effect of considering a second order contribution in β in V Q to describe the low temperature regime, we studied the WK-2 and Jaen-Khan potentials (JK), finding that WK-2 gives non-physical results and, consequently, restricting our study to the the JK model, given by…”

“…1 Properties of fluids are strongly modified when they are confined, since atoms and molecules adsorbed onto a surface display a different potential energy between themselves as compared to their energy when they are in a bulk phase; 2 in consequence, the phase diagram of the confined fluid is modified and the critical temperature is reduced; experimental values of the ratio of the critical temperatures (adsorbed fluid/bulk fluid) vary around 0.4 for a wide range of molecular fluids. [3][4][5] In this way, surfaces work as energy reservoirs that allow different conditions for the realization of phase transitions as well as the appearance of novel phases.…”

Physical adsorption of multilayer films on planar substrates and inside cylindrical pores

“…The nature of a physisorbed film is a subject of much current attention. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] In the case of a thick liquid film which wets the substrate, multilayer film adsorption becomes a particularly interesting system to study because of its apparent simplicity. One might expect here the substrate to present only a minor perturbation on the thermodynamic properties of the film.…”