Wetting in Binary Fluid Mixtures: Recent Results in H2/He on Cesium

Abstract

We present the resugts of an experiment on the wetting of liquid hydrogen on a cesium substrate using helium as a surfactant. In contrast to the previously studied case of 3He-4He mixtures on cesium, there is less ambiguity about the concentration dependence of the liquid-solid surface tension, suggesting that the resugts may be more easily interpreted; however, the relatively high temperatures and pressures complicate both experiment and calculation. The thermal expansion of the liquid turns out to be a major contribution to the temperature variation of the liquid-solid surface tension. When this is taken into account, there is excellent agreement between the observed variation of the wetting temperature with helium concentration (−.31±0.01 K/bar) and the calculated value (−.30 K/bar).