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Influence of dissolved air on bubble attachment to highly oriented pyrolytic graphite

Krasowska M., Sellapperumage P. M. F., Ralston J., Beattie D. A.

Physicochemical Problems of Mineral Processing

2018

Vol. 54, iss. 1

163--173

The effect of air, dissolved in 0.1 M KCl solution, on bubble attachment to the smooth hydrophobic surface of highly oriented pyrolytic graphite was studied. The stability of a wetting film in such a system is governed by surface forces, i.e. electrostatic and van der Waals interactions. At the high ionic strength investigated, the electric double layer forces are both weak and of short range, therefore the stability of the wetting film is dominated by van der Waals interactions. The Hamaker coefficient for the highly oriented pyrolytic graphite-KCl aqueous solution-air system is negative and hence van der Waals interactions are repulsive. A repulsive force should stabilize the wetting film, preventing its rupture and bubble attachment to the highly oriented pyrolytic graphite surface. Many experimental studies have found that wetting films are not stable at graphite or coal surfaces, and air bubbles attach. In the present experiments, the stability of the wetting films decreased with increasing amount of dissolved air. The time required for film drainage, rupture, and air bubble attachment was shortened by two orders of magnitude when the experiments were performed in air saturated 0.1 M KCl solution. This instability was attributed to an increasing number of nano- and submicron- bubbles nucleated at the graphite surface. The Hamaker coefficient across the air-KCl aqueous solution-air system is positive and hence van der Waals interactions are attractive, resulting in wetting film rupture and macroscopic air bubble attachment to a highly oriented pyrolytic graphite surface decorated with resident nano- and submicro-metre bubbles.

Experimental and theoretical study on proton tunneling in jet-cooled 9-hydroxyphenalenone-CO2 van der Waals complex

Mori H., Furusawa J., Sekiya H.

Bulletin of the Polish Academy of Sciences. Chemistry

2002

Vol. 50, No. 4

451-462

The fluorescence excitation, dispersed fluorescence, and hole-burning spectra of the 9-hydroxyphenalenone (9HPO)-C(2) 1:1 complex have been measured to investigate the effects of the van der Waals interaction on proton tunneling in the So state. The Si-So electronic origin is only 4 cm (-1) red-shifted with respect to that of the monomer, suggesting that proton tunneling occurs in both the So and Si states of the 9HPO-CO(2) complex, although the tunneling splittings have not been observed in the excitation spectrum. The structure of the observed complex and its tunneling potential for the So state of 9HPO have been theoretically investigated by using the reaction surface Hamiltonian method. The intermolecular interaction significantly changes the shape of two dimensional potential energy surface along the reaction coordinates, and slightly decreases the tunneling splitting in the zero-point level.