Wetting Films on Chemically Modified Surfaces: An X-Ray Study

 Title: Wetting Films on Chemically Modified Surfaces: An X-Ray Study Author: Tidswell, I. M.; Rabedeau, T. A.; Pershan, Peter S.; Folkers, John P.; Baker, M. V.; Whitesides, George M. Note: Order does not necessarily reflect citation order of authors. Citation: Tidswell, I. M., T. A. Rabedeau, Peter S. Pershan, John P. Folkers, M. V. Baker, and George M. Whitesides. 1991. Wetting films on chemically modified surfaces: An x-ray study. Physical Review B 44(19): 10869-10879. Access Status: Full text of the requested work is not available in DASH at this time (“dark deposit”). For more information on dark deposits, see our FAQ. Full Text & Related Files: Tidswell_Wetting.pdf (2.153Mb; PDF) Abstract: The wetting of silicon wafers and silicon wafers coated with alkylsiloxane monolayers by saturated vapors of cyclohexane and methanol were studied using x-ray specular reflection. Differentially heating the substrate surface relative to the temperature of a liquid reservoir was used to probe the disjoining pressure as a function of the film thickness and surface chemistry. Uncoated silicon wafers wet completely. The variations in film thickness with $$\Delta$$T are explained exclusively in terms of the nonretarded van der Waals forces for films 10–120 Å thick. Wafers coated with methyl terminated alkylsiloxane monolayers wet incompletely, with a microscopic film 1–3 Å thick adsorbing on the surface. Changing the alkylsiloxane terminal group from -CH$$_3$$ to -CH$$_2$$OH converts the surface from incompletely to completely wet. Surfaces coated with partial monolayers of methyl terminated alkylsiloxane of greater than 50% coverage are incompletely wet by cyclohexane, with the monolayers ‘‘swelling’’ to a thickness close to that of fully extended alkane chains through incorporation of cyclohexane into the film structure. The data are consistent with a first-order transition to complete wetting upon reduction of the alkylsiloxane coverage below approximately 50%. The importance of the surface atomic layer in the promotion or suppression of complete wetting is explained in the context of van der Waals forces. Published Version: doi:10.1103/PhysRevB.44.10869 Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10357547 Downloads of this work: