Reduced water density at hydrophobic surfaces: Effect of dissolved gases
Reduced water density at hydrophobic surfaces: Effect of dissolved gases
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DOI：
10.1073/pnas.0504034102
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发表时间：
2005-07-05
影响因子：
11.1
通讯作者：
Majewski, J
中科院分区：
文献类型：
--
作者：
Doshi, DA;Watkins, EB;Majewski, J
在这里，直接非侵入性中子反射率测量揭示了存在降低的（氘化）水密度区域，疏水性硅烷-水界面处具有 S 形密度分布，该分布取决于水中溶解气体的类型和浓度。溶解气体的去除会减小水密度降低区域的宽度，而它们的重新引入会导致水密度降低区域的宽度增加。与最近的计算机模拟相比，提出了局部波动的密度分布，而排除了预先存在的纳米气泡。两个疏水表面之间存在波动的水密度降低区域以及它所导致的有吸引力的“耗尽力”可能有助于解释疏水力及其在澄清水中的报道的减少。我们的结果在数量上也与最近的动态表面力装置结果一致，该装置极大地修改了之前对流经疏水表面的水的滑移长度的估计，从微米到大约20纳米。因此，我们的观察对于协调三种截然不同类型的实验和现象大有帮助：疏水表面的水耗竭、疏水表面的水滑移以及疏水相互作用。
Here, direct noninvasive neutron reflectivity measurements reveal the presence of a reduced (deuterated) water density region, with a sigmoidal density profile at the hydrophobic silane-water interface that depends on the type and concentration of dissolved gases in the water. Removal of dissolved gases decreases the width of the reduced water density region, and their reintroduction leads to its increase. When compared with recent computer simulations, a locally fluctuating density profile is proposed, whereas preexisting nanobubbles are excluded. The presence of a fluctuating reduced water density region between two hydrophobic surfaces and the attractive "depletion force" to which it leads may help explain the hydrophobic force and its reported diminution in cleaerated water. Our results are also quantitatively consistent with recent dynamic surface force apparatus results that drastically revise previous estimates of the slip length of water flowing past hydrophobic surfaces from microns to approximate to 20 nm. Our observations, therefore, go a long way toward reconciling three quite different types of experiments and phenomena: water depletion at hydrophobic surfaces, water slip at hydrophobic surfaces, and the hydrophobic interaction.