Desorption of Spread Monolayer of 1-Dodecanol into Aqueous Sodium Dodecyl Sulfate Substrate

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Abstract
The process of desorption of dodecanol monolayer into the aqueous sodium dodecyl sulfate (SDS) solutions of varying concentrations was studied by the surface tension measurement. The rate of desorption in its early stage obeyed the simple diffusion law and the plot of logarithms of surface pressure against the square root of time showed a linear relationship. The rate constant of desorption decreased slightly and linearly with an increasing concentration of SDS up to CMC. Beyond CMC it increased rapidly and linearly owing to the increase of dodecanol solubility due to the solubilization. Further, from these rate constants and the surface tension vs. concentration curve, the diffusion coefficient of dodecanol in water and in aqueous SDS solutions, its solubilization in aqueous SDS solution and the partition coefficient of dodecanol between water and SDS micelles were calculated. Critical micelle concentration of sodium dodecyl sulfate was also determined as a break point of desorption constant vs. concentration curve.