Trapped Aqueous Films Lubricate Highly Hydrophobic Surfaces,ACS Nano

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Trapped Aqueous Films Lubricate Highly Hydrophobic Surfaces
ACS Nano ( IF 15.8 ) Pub Date : 2018-09-25 00:00:00 , DOI: 10.1021/acsnano.8b04735
Irit Rosenhek-Goldian ₁ , Nir Kampf ₁ , Jacob Klein ₁

Affiliation

Friction at hydrophobic surfaces in aqueous media is ubiquitous (e.g., prosthetic implants, contact lenses, microfluidic devices, biological tissue) but is not well understood. Here, we measure directly, using a surface force balance, both normal stresses and sliding friction in an aqueous environment between a hydrophilic surface (single-crystal mica) and the stable, molecularly smooth, highly hydrophobic surface of a spin-cast fluoropolymer film. Normal force versus surface separation profiles indicate a high negative charge density at the water-immersed fluoropolymer surface, consistent with previous studies. Sliding of the compressed surfaces under water or in physiological-level salt solution (0.1 M NaCl) reveals strikingly low boundary friction (friction coefficient μ ≈ 0.003–0.009) up to contact pressures of at least 50 atm. This is attributed largely to hydrated counterions (protons and Na⁺ ions) trapped in thin interfacial films between the compressed, sliding surfaces. Our results reveal how frictional dissipation may occur at hydrophobic surfaces in water and how modification of such surfaces may suppress this dissipation.

中文翻译：

被困的水膜润滑高度疏水的表面

水性介质中疏水表面的摩擦是普遍存在的（例如，假体植入物，隐形眼镜，微流控装置，生物组织），但尚未广为人知。在这里，我们使用表面力平衡直接测量亲水环境（单晶云母）和旋涂含氟聚合物薄膜的稳定，分子光滑，高度疏水性表面之间在水环境中的正应力和滑动摩擦。法向力与表面分离曲线表明在水浸式含氟聚合物表面有很高的负电荷密度，这与以前的研究一致。在水下或生理水平的盐溶液（0.1 M NaCl）中，受压表面的滑动显示出极低的边界摩擦（摩擦系数μ≈0.003-0.009），直至至少50 atm的接触压力。这主要归因于困在压缩滑动表面之间的薄界面膜中的水合抗衡离子（质子和Na ⁺离子）。我们的结果揭示了摩擦耗散如何在水中的疏水性表面发生以及如何修饰此类表面可以抑制这种耗散性。

更新日期：2018-09-25

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