On the formation and structure of self-assembling monolayers: III. Time of formation, solvent retention, and release

doi:10.1016/0021-9797(86)90114-1

Journal of Colloid and Interface Science

Volume 112, Issue 2, August 1986, Pages 457-472

https://doi.org/10.1016/0021-9797(86)90114-1 Get rights and content

Abstract

FTIR spectroscopy (in the ATR mode) and contact angle measurements are used to determine the characteristic time scales of formation of some representative oleophobic monolayers produced on polar solids by spontaneous adsorption from organic solutions, and to investigate the mechanis of solvent incorporation into such organized films during their formation and its subsequent release. The more general question of adsorption of low-energy surfaces, not wetted by the bulk liquid adsorbate, is also addressed, in connection with the present observations of solvent retention on surfaces coated with nonwettable oleophobic monolayers. Two amphiphile/solid systems and two saturated hydrocarbon solvents were selected for this study, with the purpose of providing examples for different modes of binding to the surface and different geometrical relationships between solvent and amphiphile molecules. Ionic binding (arachidic acid/ZnSe) is found to yield practically complete monolayers within immersoin times not longer than 15 s, whereas several minutes are required for the formation of complete monolayers involving covalent binding to the surface (n-octadecyltrichlorosilane/Si). Solvent incorporation into the films during their formation is facilitated by geometrical matching between the solvent and the non polar portion of the amphiphile, as indicated by the observed differences between n-hexadecane and bicyclohexyl in this respect. Most of the solvent is usually squeezed out of the inner core of the film and replaced by amphiphile, with the completion of a compact and continuous monolayer of the latter. However, in some of the studied systems, variable amounts of solvent were found to be retained on top of the outer monolayer surface after its separation from the bulk liquid phase. Liquid retention on such nonwettable surfaces appears to involve adhesion at microscopic defect sites in the film. It is, finally, demonstrated that high qualtiy, solvent-free monolayers may be obtained by adsorption from organic solutions, provided geometrical matching between solvent and amphiphile is avoided and amphiphiles capable of irreversible binding to the surface are employed.

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On the formation and structure of self-assembling monolayers: III. Time of formation, solvent retention, and release

Abstract

J. Colloid Interface Sci.

J. Colloid Interface Sci.

Israel J. Chem.

Israel J. Chem.

J. Phys. Chem.

J. Phys. Chem.

J. Amer. Chem. Soc.

Langmuir

Langmuir

Thin Solid Films

Thin Solid Films

J. Amer. Chem. Soc.

J. Phys. Chem.