Adsorption of alkanes from the vapour phase on water drops measured by drop profile analysis tensiometry

Abstract

In this paper it is demonstrated that short chain alkanes (pentane, hexane, heptane, octane) can be adsorbed from a saturated vapour phase at the water-air interface. Measurements with the drop profile analysis tensiometry demonstrate that this molecular adsorption transfers into a condensation leading to a thin alkane film at the drop surface. At sufficient amounts, i.e. after such a film has reached a respective thickness, the condensed liquid starts to drain and an oil lens of alkane is formed at the water drop apex. The formation of such oil lenses is visually observed and leads to the situation that the obtained surface tensions are only effective values because the Laplace equation of capillarity does no longer describe the profile of the drop/oil lens. This is clearly demonstrated by the standard deviation of the profile fitting and the distribution of the deviation between experimental and calculated profile.

Mixed Protein/Hexane Adsorption Layers Formed at the Surface of Protein Solution Drops Surrounded by Hexane Vapor

“…[1][2][3][4][5][6][7][8][9] In all these studies, the adsorption of alkane was shown to result in a significant decrease of the surface tension. [1][2][3][4][5][6][7][8][9] In all these studies, the adsorption of alkane was shown to result in a significant decrease of the surface tension.…”

“…The adsorption of alkane vapor from the gas phase at the surface of pure water drops was extensively studied for alkanes of various chain lengths and for different partial pressures of alkanes in the gas phase. [1][2][3][4][5][6][7][8][9] In all these studies, the adsorption of alkane was shown to result in a significant decrease of the surface tension. In ref.…”

Multilayer Adsorption of Heptane Vapor at Water Drop Surfaces

“…Various experimental and theoretical studies of adsorption of alkanes from the gas phase on a water surface were previously reported [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The thickness of such adsorbed alkane layers was determined with optical methods being maximum up to 4-5 nm [6].…”

“…During last years, a large pool of experimental data was collected, and theoretical models were developed for the adsorption of alkanes from the gas phase on the surface of a water drop [7][8][9][10][11][12][13][14][15][16][17]. It was shown, for instance, that the adsorption of alkanes from the gas phase results in a significant decrease of the surface tension of water or aqueous protein (surfactant) solutions.…”

“…It was shown, for instance, that the adsorption of alkanes from the gas phase results in a significant decrease of the surface tension of water or aqueous protein (surfactant) solutions. Moreover, measurements and analysis of tensiometric data [7] demonstrated that the adsorption of alkanes on the surface of water drops can lead to a condensation of the alkane molecules at the surface and to the formation of liquid films. It was shown [12] that the influence of hexane vapor on the surface tension of water depends also essentially on the air humidity.…”