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Download fileWhy do aqueous surfactant solutions spread over hydrophobic substrates?
journal contribution
posted on 2011-01-05, 17:19 authored by Victor Starov, Natalia A. Ivanova, Ramon RubioSpreading of aqueous surfactant solution droplets over hydrophobic substrates proceeds in one slow stage at
concentration of surfactants below some critical value and in two stages if the surfactant concentration is
above the critical value: the fast and relatively short first stage is followed by a slower second stage. It is
shown that the kinetics of a slow spreading at concentrations below the critical value and the second stage at
concentrations above the critical value are determined by a transfer of surfactant molecules on a bare
hydrophobic substrate in front of the moving three-phase contact line (autophilic phenomenon). The latter
process results in an increase of the solid–vapour interfacial tension of the hydrophobic solid surface in front
of the moving three-phase contact line and spreading as a result. It is proven that the adsorption of surfactant
molecules in front of the moving three-phase contact line results in a decrease of the total free energy of the
droplet. Hence, the adsorption of surfactants molecules on a bare hydrophobic substrate in front of the
moving three-phase contact line is a spontaneous process in spite of an increase of the local solid–vapour
interfacial tension. The duration of the first stage of spreading in the case of the surfactant concentration
above the critical value correlates well with the duration of adsorption of surfactant molecules onto a liquid–
vapour interface. The latter allows assuming that the adsorption on the liquid–vapour interface is the driving
mechanism of spreading during the first fast stage of spreading at surfactant concentrations above the critical
value. It is discussed why the first stage of spreading does not take place in the case of surfactant
concentrations below the critical concentration in spite of the longer duration of adsorption on liquid–
vapour interface in this case.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Chemical Engineering
Citation
STAROV, V., IVANOVA, N.A. and RUBIO, R.G., 2010. Why do aqueous surfactant solutions spread over hydrophobic substrates? Advances in Colloid and Interface Science, 161 (1-2), pp. 153-162.Publisher
© ElsevierVersion
- AM (Accepted Manuscript)
Publication date
2010ISSN
0001-8686Publisher version
Language
- en