What determines the size of liquid capillary condensates below the bulk melting point?

金沢大学理工研究域物質化学系Capillary condensation from vapor has been studied at temperatures below the bulk melting point Tm of the condensing substance using a surface force apparatus. Both mica and mica modified by self-assembly of a fluorinated surfactant (perfluoro-1H,1H,2H,2H-decylpyridinium chloride) have been used as substrate surfaces. The condensing liquids, cyclooctane and menthol, nearly wet (contact angle <15°) mica but show a high (∼60°) contact angle on the fluorinated surface. As in previous studies with unmodified mica, we find that both cyclooctane and menthol condense as liquids below Tm, and that the size of the condensates at solid-vapor coexistence is limited and inversely proportional to the temperature depression below Tm, or Ar. A comparison of the size of the condensates between the fluorocarbon surfaces and the mica surfaces and the quantitative dependence of the size of the condensate on ΔT for cyclooctane lead us to conclude that the maximum condensate size is determined by the equilibrium between condensed, "supercooled" liquid and vapor, and is hence proportional to the surface tension of the liquid-vapor interface. From a consideration of the equilibrium between a liquid and a hypothetical solid condensate, it is concluded that a solid condensate does not usually form for kinetic reasons although two exceptions were found in earlier work. © 2007 American Chemical Society

Adsorption from pure and mixed vapours of n-hexane and n-perfluorohexane

We have used a modified surface force apparatus (SFA) to study adsorption onto mica surfaces from near-saturated vapours of $n$-hexane and $n$-perfluorohexane, and mixtures thereof. For relative vapour pressures in the range 0.9-0.998 the films adsorbed from vapours of the pure liquids range in thickness from 1 to 4 nm, in crude agreement with the predictions of non-retarded van der Waals-Lifshitz theory. The observed deviations from theory show a qualitative difference between the two liquids, which may reflect differences in the significance of structural contributions to the disjoining pressure. Under the same experimental conditions, adsorption from vapours of (one-phase) liquid mixtures gives rise to films which are significantly thicker, over a broad range of intermediate compositions, than those adsorbed from the pure vapours, with a broad maximum in thickness observed near the critical composition of the bulk liquid mixture

Neutron reflectivity studies of critical adsorption behaviour of the surface scaling function

Neutron reflectometry has been employed to examine the nature of the critical adsorption surface scaling function for a near critical mixture of hexane d14 perfluorohexane adsorbing to a solid substrate from the liquid one phase region. The analysis method of Dietrich and Schack has been applied to examine the nature of the power law part of the critical adsorption surface scaling function, which has been found to behave as m z P0z amp; 8722;m as the critical point is approached. Values of m 0.514 0.018 and P0 0.90 0.04 have been obtained. These values are consistent with theoretical expectations mth 0.516 0.004; P0th 0.94 0.05 , the value determined from Monte Carlo simulations P0MC 0.866 , and other experimental determinations P0ex 0.955 0.0