Desorption from slightly soluble monolayer

Abstract

Summary:The desorption from slightly soluble spread monolayers at the air/water interface is studied by compressing the monolayer suddenly, whereafter the surface tension is followed as a function of time. As far as the deviation from equilibrium is small a relation is obtained giving the transient surface tensions with time. This relation is obtained from the modulus of elasticity by inverse Fourier transformation. Two relaxation mechanisms are presented, in one the transfer from the monolayer to the subsurface is the rate limiting step (barrier), in the other the diffusion from the subsurface to the bulk is the rate limiting step (diffusion controlled). It was found that for lauric acid, myristic acid, the bile acids and 1-12 didodecanoic acid, the desorption process is diffusion controlled and good agreement between theory and experiment is obtained.Abstract: An equation is presented to give the dynamic surface tension with time for diffusion controlled adsorption/desorption processes. Principally, this equation is only valid for small deviations from the equilibrium surface tensions. In practice however this restriction is not so severe. The theory is tested for desorption of slightly soluble spread monolayers of lauric and myristic acid, cholic, desoxycholic and lithocholic acid and for 1-12 dodecanoic acid. Excellent agreement is achieved.

Adsorption Kinetics of Some Polyethylene Glycol Octylphenyl Ethers Studied by the Fast Formed Drop Technique

“…Since we kept (0) = 0, our solution (i.e., Eq. [4]) differs from that of Joos et al (17,18) by the term 1 − (0)/ e . Hence, the slope of the line σ = σ (t −1/2 ) defined by Eq.…”

“…[2] can be easily integrated and a long time approximated solution can be obtained. The solution derived by Joos et al (17,18) has been compared with other approximate solutions in Ref. (19), where its reliability for interpretation of the kinetic data at long periods of time is discussed.…”

“…Following the approach of Joos et al (17,18), i.e., assuming that c s ∼ = const. at long periods of time, Eq.…”

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“…The solid lines in these figures show the good fit of the data to single exponential decays. For a diffusion controlled process, the dynamic interfacial tension should vary with time according to equation 3 26 :…”

Study of the dynamic interfacial tension at the oil/water interface

“…(17) At the air/water interface it is possible to use the well established stress-relaxation method [1] in a Langmuir trough [31]. (17) At the air/water interface it is possible to use the well established stress-relaxation method [1] in a Langmuir trough [31].…”