Department of Chemical and Materials Engineering , University of Alberta , Edmonton , Alberta T6G 1H9 , Canada.
Langmuir. 2018 Nov 27;34(47):14196-14203. doi: 10.1021/acs.langmuir.8b02636. Epub 2018 Nov 9.
Pushing the boundaries of the investigation of hydrophobic attraction (HA) to the molecular scale readily ensures the collection of experimental results free of secondary effects, thereby facilitating the unraveling of the underlying mechanism by providing clean experimental results that truly reflect the hydrophobic attraction. Regardless of the feasibility of this approach, investigations using this promising method are stagnant due to the difficulties in determining the individual contributions of HA and van der Waals (vdW) interactions at the molecular scale. Here, a novel approach was proposed for the first time to determine the individual contributions of vdW interactions and HA by studying the single-molecule adhesion forces of a neutral oligo ethylene glycol methacrylate copolymer on a MoS crystal exposed to different water chemistry. The anisotropic surface properties of MoS enabled the partitioning of vdW interactions and hydrophobic attraction in total single-molecule adhesion forces and also enabled determining the contribution of electrostatic interaction (ESI). When the presence of ESI is excluded, the study of single-molecule adhesion forces using single-molecule force spectroscopy (SMFS) revealed that the contribution of vdW interactions to total molecular interactions was smaller than 9 pN. The strong single-molecule adhesion forces of oligo ethylene glycol copolymer on the hydrophobic basal surface of MoS demonstrated that HA plays a dominant role with contribution up to 89% to the total single-molecule adhesion force. By utilizing the derived theoretical model, we quantified the individual contribution of each fundamental interaction under a variety of conditions. This study proposed a facile approach to quantitatively clarify the roles of vdW interactions and HA at the molecular scale, which may help assist future experimental and theoretical investigations of hydrophobic (solvophobic) effects and vdW interactions in aqueous solutions.
将疏水吸引（HA）的研究推向分子尺度，很容易确保收集到没有二次效应的实验结果，从而通过提供真正反映疏水吸引的干净实验结果，有助于揭示潜在的机制。无论这种方法是否可行，由于在分子尺度上难以确定 HA 和范德华（vdW）相互作用的个体贡献，使用这种有前途的方法的研究都停滞不前。在这里，首次提出了一种新方法，通过研究在暴露于不同水化学的 MoS 晶体上中性聚乙二醇甲基丙烯酸酯共聚物的单个分子粘附力，来确定 vdW 相互作用和 HA 的个体贡献。MoS 的各向异性表面特性使得可以在总单分子粘附力中分配 vdW 相互作用和疏水力，并且还可以确定静电相互作用（ESI）的贡献。当排除 ESI 的存在时，使用单分子力谱（SMFS）研究单分子粘附力表明，vdW 相互作用对总分子相互作用的贡献小于 9 pN。聚乙二醇共聚物在 MoS 的疏水下基底表面上的强单分子粘附力表明，HA 起着主导作用，对总单分子粘附力的贡献高达 89%。通过利用推导的理论模型，我们在各种条件下量化了每个基本相互作用的个体贡献。这项研究提出了一种简便的方法，可以定量阐明分子尺度上 vdW 相互作用和 HA 的作用，这可能有助于协助未来对水溶液中疏水（溶剂疏水性）效应和 vdW 相互作用的实验和理论研究。
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