水薄层在常温下“结冰”| Science Advances 论文推荐

阿克伦大学的研究人员发现两个带电表面之间的水的纳米级薄层表现出类冰倾向，能够承受的压力高达几百个大气压

来源 阿克伦大学

翻译 赵迪

审校 金庄维

表面活性剂（绿色分子）构成两个带电分子层，其间的水薄层（蓝色分子）形成类冰结构，减小表面间的摩擦。Credit: TheUniversity of Akron

阿克伦大学（Universityof Akron, UA）科研人员的最新研究表明：两个带电表面之间的水的纳米级薄层表现出类冰倾向，能够承受的压力高达几百个大气压。这一发现将为各种情形下减小摩擦带来更好的方法。

为什么高压下表面间的水分子没有被直接“挤出去”？这一问题困扰人们已久。UA 的研究者发现，高压条件下两表面间自然产生的电荷将水分子困在其中，并且导致分子排列呈现类冰结构。常温下的这种类冰水层减小了表面间的摩擦。

“我们首次对这些条件下水层发生的变化以及为什么它能将两个表面分开有了基本了解。”Ali Dhinojwala教授说，“我们曾猜测这是由于分子层面上发生了变化，现在我们证实了这个想法。”

 “这一发现有助于在将低摩擦表面至关重要的情况下优化设计，比如生物医学中的膝关节移植。”UA 的研究生 Nishad Dhopatkar 说道。

另一位研究成员Adrian Defante说道：“新发现的特性也有助于抗菌涂料的发展：因为水薄层可以防止细菌附着。”

Dhinojwala教授补充道，这项研究反过来为“如何将水从两个表面间分离”提供线索，有助于增强含水环境中的粘着力。

Dhinojwala 教授团队的这项研究刊登于 Science Advances。

原文链接：http://advances.sciencemag.org/content/2/8/e1600763

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论文信息：

【题目】Ice-like water supports hydration forces andeases sliding friction

【作者】 Nishad Dhopatkar . AdrianP.Defante and Ali Dhinojwala

【刊期】Science Advance: Vol.2, No. 8, e1600763

【日期】26 Aug 2016

【doi】  10.1126/sciadv.1600763

【摘要】The nature of interfacial water is critical in severalnatural processes, including the aggregation of lipids into the bilayer,protein folding, lubrication of synovial joints, and underwater gecko adhesion.The nanometer-thin water layer trapped between two surfaces has been identifiedto have properties that are very different from those of bulk water, butthemolecular cause of such discrepancy is often undetermined. Usingsurface-sensitive sum frequency generation (SFG) spectroscopy, we discover astrongly coordinated water layer confined between two charged surfaces, formedby the adsorption of a cationic surfactant on the hydrophobic surfaces. Byvarying the adsorbed surfactant coverage and hence the surface charge density,we observe a progressively evolving water structure that minimizes the slidingfriction only beyond the surfactant concentration needed formonolayerformation. At complete surfactant coverage, the strongly coordinated confinedwater results in hydration forces, sustains confinement and sliding pressures,and reduces dynamic friction. Observing SFG signals requires breakdown incentrosymmetry, and the SFG signal from two oppositely oriented surfactantmonolayers cancels out due to symmetry. Surprisingly, we observe the SFG signalfor the water confined between the two charged surfactant monolayers,suggesting that this interfacial water layer is noncentrosymmetric. Thestructure of molecules under confinement and its macroscopic manifestation onadhesion and friction have significance inmany complicated interfacialprocesses prevalent in biology, chemistry, and engineering.

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