We present a comprehensive study of water drops sliding down chemically heterogeneous surfaces formed by a periodic pattern of alternating hydrophobic and hydrophilic stripes. Drops are found to undergo a stick-slip motion whose average speed is an order of magnitude smaller than that measured on a homogeneous surface having the same static contact angle. This motion is the result of the periodic deformations of the drop interface when crossing the stripes. Numerical simulations confirm this view and are used to elucidate the principles underlying the experimental observations.

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Isothermal scans of third-sound velocity as a function of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ coverage on graphite exhibit pronounced dips integral layer periodicity. The minimum ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ coverage on graphite needed to support third sound is nearly three layers. The heat-capacity isotherm exhibits minima at layer completion but there is no noticeable feature related to the onset of superfluidity. High-resolution adsorption isotherms below 1 K show that ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film grows layer by layer through at least seven layers.

Calculations are presented in the wetting properties of liquid hydrogen films on various substrates. The well depth D for the adsorption potential is even smaller for alkali metal substrates than for noble gas surfaces. A simple model calculation leads to the prediction that wetting transitions should then occur at a temperature ${\mathit{T}}_{\mathit{w}}$ about 20 K. Quartz microbalance data obtained for ${\mathrm{H}}_2$ on Rb are consistent with this result. Specifically, ${\mathit{T}}_{\mathit{w}}$ is found to be 17.89±0.04 K. The wetting phase diagram is found to be in good agreement with thermodynamic expectations.

Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.