Direct and quantitative AFM measurements of the concentration and temperature dependence of the hydrophobic force law at nanoscopic contacts.
Direct and quantitative AFM measurements of the concentration and temperature dependence of the hydrophobic force law at nanoscopic contacts.
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DOI：
10.1016/j.jcis.2015.01.032
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发表时间：
2015-05
影响因子：
9.9
通讯作者：
P. Stock;Thomas Utzig;M. Valtiner
中科院分区：
文献类型：
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作者：
P. Stock;Thomas Utzig;M. Valtiner
由于其对生物物质自组织的重要性，疏水力定律和疏水相互作用 (HI) 的范围在过去 40 年中一直受到广泛争论。在这里，我们直接测量和量化大温度和浓度范围内的疏水力-距离定律。特别是，我们研究了分子光滑疏水自组装单层和类似改性的镀金 AFM 尖端（半径 ~ 8–50 nm）之间的 HI。我们提供了定量和直接的证据，表明疏水力是长程的，并且在大约 1-2 nm 的距离内呈指数增长。因此，我们为原子力显微镜数据引入了自洽半径归一化。这种方法允许将基于 AFM 的实验数据定量数据拟合到最近提出的 Hydra 模型。我们的拟合和数据的统计显着性为 r2⩾ 0.96，直接显示指数 HI 衰减长度为 7.2 ± 1.2 Å，与高达 750 mM 的盐浓度无关。因此，静电屏蔽对 1 mM 至 750 mM 电解质浓度范围内的 HI 没有显着影响。在 1 M 溶液中，观察到的不稳定性在接近过程中转移到更长的距离，表明高盐浓度下的离子关联/吸附效应。随着温度的升高，HI 的幅度单调减小，而范围略有增加。我们将我们的结果与大量现有文献进行比较，并为非常近的距离和宽温度和浓度范围内疏水相互作用的范围和强度提供了新的线索。
By virtue of its importance for self-organization of biological matter the hydrophobic force law and the range of hydrophobic interactions (HI) have been debated extensively over the last 40 years. Here, we directly measure and quantify the hydrophobic force–distance law over large temperature and concentration ranges. In particular, we study the HI between molecularly smooth hydrophobic self-assembled monolayers, and similarly modified gold-coated AFM tips (radii ∼ 8–50 nm). We present quantitative and direct evidence that the hydrophobic force is both long-ranged and exponential down to distances of about 1–2 nm. Therefore, we introduce a self-consistent radius-normalization for atomic force microscopy data. This approach allows quantitative data fitting of AFM-based experimental data to the recently proposed Hydra-model. With a statistical significance ofr2⩾ 0.96 our fitting and data directly reveal an exponential HI decay length of 7.2 ± 1.2 Å that is independent of the salt concentration up to 750 mM. As such, electrostatic screening does not have a significant influence on the HI in electrolyte concentrations ranging from 1 mM to 750 mM. In 1 M solutions the observed instability during approach shifts to longer distances, indicating ion correlation/adsorption effects at high salt concentrations. With increasing temperature the magnitude of HI decreases monotonically, while the range increases slightly. We compare our results to the large body of available literature, and shed new light into range and magnitude of hydrophobic interactions at very close distances and over wide temperature and concentration regimes.