Interface-Induced Ordering of Gas Molecules Confined in a Small Space
Ing-Shouh Hwang1*, Yi-Hsien Lu1, Chih-Wen Yang1, Chung-Kai Fang1, Hsien-Chen Ko1
1Institute of Physics, Academia Sinica, Taipei, Taiwan
* presenting author:Ing-Shouh Hwang, email:ishwang@phys.sinica.edu.tw
The thermodynamic properties of gases have been understood primarily through phase diagrams of bulk gases. However, observations of gases confined in a nanometer space have posed a challenge to the principles of classical thermodynamics. Here, we investigated interfacial structures comprising either O2 or N2 between water and a hydrophobic solid surface by using advanced atomic force microscopy techniques. Ordered epitaxial layers and cap-shaped nanostructures were observed. In addition, pancake-shaped disordered layers that had grown on top of the epitaxial base layers were observed in oxygen-supersaturated water. We propose that hydrophobic solid surfaces provide low-chemical-potential sites at which gas molecules dissolved in water can be adsorbed. The structures are further stabilized by interfacial water. Here we show that gas molecules can agglomerate into a condensed form when confined in a sufficiently small space under ambient conditions. The crystalline solid surface may even induce a solid-gas state when the gas-substrate interaction is significantly stronger than the gas-gas interaction. The ordering and thermodynamic properties of the confined gases are determined primarily according to interfacial interactions [1].

[References]
1. Yi-Hsien Lu, Chih-Wen Yang, Chung-Kai Fang, Hsien-Chen Ko, and Ing-Shouh Hwang*, “Interface-Induced Ordering of Gas Molecules Confined in a Small Space”, Scientic Reports 4, 7189 (2014)


Keywords: hydrophobic/water interface, water, gas, atomic force microscopy