Order-parameter kinetics in the liquid-gas coexistence region of Ar monolayers physisorbed on graphite

Abstract

Liquid Ar submonolayers physisorbed on graphite have been studied by ellipsometry. The layers have been evaporated by means of laser pulses and the time evolution of the coverage upon readsorption has been studied as a function of temperature (T <Tc) and bulk gas pressure.PACS numbers: 68.10Jy, 05.50.+q, 64.60.Cn, 82.65.Dp Recently there has been intense theoretical interest in the relaxations of states far from thermal equilibrium [l]. A fundamental problem in this field is the temporal decay of an unstable state which is prepared by a quench into a coexistence region below a critical point, such as the gasliquid coexistence of a van der Waals system or the coexistence of up and down domains in a ferromagnet. We will report measurements on the transients of the coverage 0 through the coexistence region of the two dimensional (2D) gas and the 2D liquid phase of submonolayers of Ar physisorbed on graphite.Only a few experiments on the kinetics involving phase transitions of 2D systems have been reported so far in the literature [2]. As far as we know they all deal with structural relaxations due to site changes of chemisorbed adatoms which have been induced by changes of temperature at fixed coverage [3,4], whereas in the present case the temperature is constant and the changes of coverage are due to merely relaxational dynamics. In addition, the present experiment is carried out in a critical regime.The relevant thermodynamic variables of the present experiment are the coverage 0 and the temperature T of the adsorbed Ar submonolayers and the pressure p of the bulk Ar gas in the vacuum chamber. 0 is measured by an ellipsometer in terms of the ellipsometric phase shift 5A

Water in Nanopores: III. Surface Phase Transitions of Water on Hydrophilic Surfaces

“…With increasing of the layer number, the critical temperature of the layering transition may increase or decrease when approaching the roughening temperature. Some of the coexistence curves of the layering transitions obtained experimentally − were fitted to the simple scaling law where p is the order parameter, which measures a dissimilarity of the coexisting phases, and β is the critical exponent. The values of β obtained from the fits varied from about 0.10 to 0.20, in reasonable agreement with β = 0.125, expected for the critical behavior of 2D systems.…”