Thickness, Composition, and Molecular Structure of Residual Thin Films Formed by Forced Dewetting of Ag from Glycerol/D2O Solutions

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• 作者：Jeanne E. Pemberton ; Anoma Mudalige ; Heemin Yoo
• 刊名：Langmuir
• 出版年：2014
• 出版时间：December 23, 2014
• 年：2014
• 卷：30
• 期：50
• 页码：15181-15192
• 全文大小：561K
• ISSN：1520-5827

文摘

The thickness, composition, and interfacial molecular structure of residual thin films retained on the surface of polycrystalline Ag substrates after being forcibly dewet from glycerol/D₂O solutions are investigated using contact angle measurements, ellipsometry, and polarization modulation-infrared reflection鈥揳bsorption spectroscopy (PM-IRRAS). Residual film thicknesses are rationalized on the basis of the relevant long-range van der Waals and structural forces leading to residual film formation along with the interfacial glycerol and D₂O structure. Unique interfacial composition, wherein glycerol preferentially segregates to the residual film interfaces, is substantiated by PM-IRRAS. Thus, the residual films possess composition and molecular structure that differ from those of bulk solution. Specifically, in the thinnest residual films, glycerol interacts strongly with the Ag substrate, leading to glycerol that is more ordered than the bulk liquid that coexists with bulk-like D₂O. In thicker residual films, the glycerol mole fraction is still enhanced relative to the bulk solution, but both ordered and liquid-like glycerol species are observed along with D₂O that is more strongly hydrogen-bonded than in the bulk. The creation of residual films by forced dewetting and their interrogation by spectroscopic methods are thus demonstrated to represent a powerful approach for characterizing interfacial liquid molecular structure near solid surfaces but beyond the first monolayer under ambient conditions.