Desorption at constant surface pressure from slightly soluble monolayers

• Published in: Journal of colloid and interface science Vol. 91; no. 1; pp. 131 - 137
• Main Authors: De Keyser, P, Joos, P
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1983
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(83)90320-X

The desorption of a slightly soluble monolayer, spread at the air/water interface, is considered by keeping the surface pressure constant while decreasing the area. As already observed by other investigators, the curve giving the logarithm of the area with time can be derived in three regimes. In a first one, for small times, the logarithm of the area decreases linearly with the square root of time. In a second one, for large times, the logarithm of the area decreases linearly with time. And finally a third one for the transition between both regimes (for intermediate times). For the first and second regimes a theory is presented, which allows the diffusion coefficient to be obtained from experimental data. The desorption process is diffusion controlled, and there is no need to postulate an adsorption—desorption barrier, at least for the surfactants considered (lauric acid, decanol, and dodecanol).