Supercritical Casimir effect in carbon dioxide

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• 作者：E. Schurtenberger ; M. Heuberger
• 关键词：Critical Casimir effect ; Confined CO2 ; Supercritical ridge ; Density fluctuation depletion ; Cavitation ; Surface forces ; CO2 solvent
• 刊名：The Journal of Supercritical Fluids
• 出版年：2012
• 出版时间：November, 2012
• 年：2012
• 卷：71
• 期：Complete
• 页码：120-126
• 全文大小：783 K

文摘

We present the first measurement of surface forces across supercritical carbon dioxide. An important finding is that long-range attractive surface forces are detected not just near the critical point, but along the supercritical extension of the coexistence line, which is commonly discussed as the supercritical ridge.

Using a precisely adjustable model slit pore, our experiment can measure the change of thermodynamic potential together with changes in refractive index (mass density) in the confined CO₂. The model slit pore is realized between two atomically smooth mica surfaces in a specially designed high-pressure surface forces apparatus. Our data suggest that thermal fluctuations of higher density are selectively depleted, which results in observation of a time- and space-averaged density reduction in the confined film. Direct observation of this confinement effect has consequences for theoretical understanding as well as technological applications of CO₂ in porous materials.

In the presence of small amounts of an acrylate solute (polyethyleneglycol-dimethacrylate), we found that multiple stable menisci of solute can be created between the surfaces and stretched out several micrometers. These liquid-liquid bridges are observed as an apparent birefringence effect. We demonstrate the critical character of the phenomena and discuss our findings in terms of a (super)critical Casimir effect.