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Excess thermodynamic properties of thin water films confined between hydrophobized gold surfaces
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
2011 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 364, no 1, 257-263 p.Article in journal (Refereed) Published
Abstract [en]

Surface forces between gold surfaces were measured in pure water at temperatures in the range of 10-40 degrees C using an atomic force microscope (AFM). The surfaces were hydrophobized by self-assembly of alkanethiols (C(n)SH) with n = 2 and 16 in ethanol solutions. The data were used to determine the changes in excess free energies (Delta G(f)) of the thin water films per unit area by using the Derjaguin approximation [1]. The free energy data were then used to determine the changes in excess film entropy (Delta S(f)) and the excess film enthalpy (Delta H(f)) per unit area. The results show that both Delta S(f) and Delta H(f) decrease with decreasing film thickness, suggesting that the macroscopic hydrophobic interaction involves building some kind of structures in the intervening thin films of water. It was found that vertical bar Delta H(f)vertical bar > vertical bar T Delta S(f)vertical bar, which is a necessary condition for an attractive force to appear when the enthalpy and entropy changes are both negative. That macroscopic hydrophobic interaction is enthalpically driven is contrary to the hydrophobic interactions at molecular scale. The results obtained in the present work are used to discuss possible origins for the long-range attractions observed between hydrophobic surfaces.

Place, publisher, year, edition, pages
2011. Vol. 364, no 1, 257-263 p.
Keyword [en]
Enthalpy-entropy compensation, Alkanethiol, Surface force, Hydrophobic force, DLVO theory, Temperature effect, Thin films of water, Low-density liquid (LDL), Clathrate
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-51271DOI: 10.1016/j.jcis.2011.08.027ISI: 000296038600033ScopusID: 2-s2.0-80053208643OAI: diva2:464044
QC 20111212Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2011-12-12Bibliographically approved

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Eriksson, Jan Christer
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