Molecular explanation for why talc surfaces can be both hydrophilic and hydrophobic.
Molecular explanation for why talc surfaces can be both hydrophilic and hydrophobic.
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DOI：
10.1021/ja208687a
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发表时间：
2011-12-21
影响因子：
15
通讯作者：
Chandler, David
中科院分区：
文献类型：
--
作者：
Rotenberg, Benjamin;Patel, Amish J.;Chandler, David
虽然单个水分子强烈吸附在滑石表面上（亲水行为），但水滴在同一表面上形成珠状（疏水行为）。为了使这种二分法合理化，我们研究了表面的微观结构和粘合剂（表面-水）相互作用的强度对表面疏水性的影响。我们发现，在低相对湿度下，粘附力和处于气相的有利熵之间的竞争决定了表面覆盖度。然而，在饱和时，粘附力和内聚力（水-水相互作用）之间的竞争决定了表面疏水性。滑石中的粘附相互作用足够强以克服不利熵，并且水在滑石表面上强烈吸附。然而，它们太弱而不能克服内聚相互作用，因此水在滑石表面上成珠。令人惊讶的是，即使是高度粘合的（滑石类）表面，在饱和时也不会完全润湿。相反，水滴形成在强烈吸附的单层水的顶部。我们的研究结果表明，内部的疏水沸石悬浮在水中可能含有吸附的水分子在压力远小于入侵压力。
While individual water molecules adsorb strongly on a talc surface (hydrophilic behavior), a droplet of water beads up on the same surface (hydrophobic behavior). To rationalize this dichotomy, we investigate the influence of the microscopic structure of the surface and the strength of adhesive (surface-water) interactions on surface hydrophobicity. We show that at low relative humidity, the competition between adhesion and the favorable entropy of being in the vapor phase determines the surface coverage. However, at saturation, it is the competition between adhesion and cohesion (water-water interactions) that determines surface hydrophobicity. The adhesive interactions in talc are strong enough to overcome the unfavorable entropy, and water adsorbs strongly on talc surfaces. However, they are too weak to overcome the cohesive interactions, and water thus beads up on talc surfaces. Surprisingly, even (talc-like) surfaces that are highly adhesive, do not fully wet at saturation. Instead, a water droplet forms on top of a strongly adsorbed monolayer of water. Our results imply that the interior of hydrophobic zeolites suspended in water may contain adsorbed water molecules at pressures much smaller than the intrusion pressure.
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