Surface Behavior of Boronic Acid-Terminated Silicones

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• 作者：Erum Mansuri ; Laura Zepeda-Velazquez ; Rolf Schmidt ; Michael A. Brook ; Christine E. DeWolf
• 刊名：Langmuir
• 出版年：2015
• 出版时间：September 1, 2015
• 年：2015
• 卷：31
• 期：34
• 页码：9331-9339
• 全文大小：523K
• ISSN：1520-5827

文摘

Silicone polymers, with their high flexibility, lie in a monolayer at the air鈥搘ater interface as they are compressed until a critical pressure is reached, at which point multilayers are formed. Surface pressure measurements demonstrate that, in contrast, silicones that are end-modified with polar groups take up lower surface areas under compression because the polar groups submerge into the water phase. Boronic acids have the ability to undergo coordination with Lewis bases. As part of a program to examine the surface properties of boronic acids, we have prepared boronic acid-modified silicones (SiBAs) and examined them at the air鈥搘ater interface to better understand if they behave like other end-functional silicones. Monolayers of silicones, aminopropylsilicones, and SiBAs were characterized at the air鈥搘ater interface as a function of end functionalization and silicone chain length. Brewster angle and atomic force microscopies confirm domain formation and similar film morphologies for both functionalized and non-functionalized silicone chains. There is a critical surface pressure (10 mN m^鈥?) independent of chain length that corresponds to a first-order phase transition. Below this transition, the film appears to be a homogeneous monolayer, whose thickness is independent of the chain length. Ellipsometry at the air鈥搘ater interface indicates that the boronic acid functionality leads to a significant increase of film thickness at low molecular areas that is not seen for non-functionalized silicone chains. What differentiates the boronic acids from simple silicones or other end-functionalized silicones, in particular, is the larger area occupied by the headgroup when under compression compared to other or non-end-functionalized silicones, which suggests an in-plane rather than submerged orientation that may be driven by boronic acid self-complexation.