Tuteja Anish, Choi Wonjae, Mabry Joseph M, McKinley Gareth H, Cohen Robert E
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Proc Natl Acad Sci U S A. 2008 Nov 25;105(47):18200-5. doi: 10.1073/pnas.0804872105. Epub 2008 Nov 10.
Superhydrophobic surfaces display water contact angles greater than 150 degrees in conjunction with low contact angle hysteresis. Microscopic pockets of air trapped beneath the water droplets placed on these surfaces lead to a composite solid-liquid-air interface in thermodynamic equilibrium. Previous experimental and theoretical studies suggest that it may not be possible to form similar fully-equilibrated, composite interfaces with drops of liquids, such as alkanes or alcohols, that possess significantly lower surface tension than water (gamma(lv) = 72.1 mN/m). In this work we develop surfaces possessing re-entrant texture that can support strongly metastable composite solid-liquid-air interfaces, even with very low surface tension liquids such as pentane (gamma(lv) = 15.7 mN/m). Furthermore, we propose four design parameters that predict the measured contact angles for a liquid droplet on a textured surface, as well as the robustness of the composite interface, based on the properties of the solid surface and the contacting liquid. These design parameters allow us to produce two different families of re-entrant surfaces- randomly-deposited electrospun fiber mats and precisely fabricated microhoodoo surfaces-that can each support a robust composite interface with essentially any liquid. These omniphobic surfaces display contact angles greater than 150 degrees and low contact angle hysteresis with both polar and nonpolar liquids possessing a wide range of surface tensions.
超疏水表面具有大于150度的水接触角以及低接触角滞后现象。放置在这些表面上的水滴下方捕获的微小空气袋导致处于热力学平衡的复合固-液-气界面。先前的实验和理论研究表明,对于表面张力比水(γ(lv)=72.1 mN/m)低得多的液体(如烷烃或醇)的液滴,可能无法形成类似的完全平衡的复合界面。在这项工作中,我们开发了具有凹角纹理的表面,即使对于表面张力非常低的液体(如戊烷,γ(lv)=15.7 mN/m),也能支持强亚稳态复合固-液-气界面。此外,我们提出了四个设计参数,基于固体表面和接触液体的特性,预测纹理表面上液滴的测量接触角以及复合界面的稳健性。这些设计参数使我们能够生产两种不同类型的凹角表面——随机沉积的电纺纤维垫和精确制造的微石林表面——它们各自都能与基本上任何液体形成稳健的复合界面。这些全憎表面对于具有广泛表面张力的极性和非极性液体都显示出大于150度的接触角和低接触角滞后现象。