Division of Material Chemistry, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. Bio-AFM Frontier Research Center, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. PRESTO, JST, Kawaguchi, 332-0012, Japan.
Nanotechnology. 2017 Nov 10;28(45):455603. doi: 10.1088/1361-6528/aa8aa7.
A molecular-scale understanding of self-assembled monolayers (SAMs) of sulfonate-terminated alkanethiols is crucial for interfacial studies of functionalized SAMs and their various applications. However, such an understanding has been difficult to achieve because of the lack of direct information on these molecular-scale structures in real space. In this study, we investigated the structures of sulfonate SAMs of sodium 11-mercapto-1-undecanesulfonate (MUS) by frequency modulation atomic force microscopy (FM-AFM) in liquid. The subnanometer-resolution FM-AFM images showed that the single-component MUS SAM prepared in pure water had random surface structures. In contrast, the MUS SAM prepared in a water-ethanol mixed solvent showed periodic striped structures with a flat-lying conformation. The results suggest a significant solvent effect on molecular-scale structures of long-chain sulfonate SAMs. In addition, we investigated the molecular-scale structures of mixed SAMs of MUS and 11-mercapto-1-undecanol (MUO) with alkane chains of the same length. The FM-AFM images of the mixed SAMs showed clear phase separation between MUS SAM and MUO SAM domains. In the MUO SAM domains, the incorporated MUS molecules appeared as protrusions. The results obtained in this study provide direct structural information on long-chain sulfonate and mixed SAMs.
磺酸酯封端的烷硫醇自组装单分子层（SAMs）的分子尺度理解对于功能化 SAMs 及其各种应用的界面研究至关重要。然而，由于缺乏有关这些分子尺度结构在真实空间中的直接信息，因此很难实现这种理解。在这项研究中，我们通过调频原子力显微镜（FM-AFM）在液体中研究了磺酸酯 SAMs 的结构。亚纳米分辨率的 FM-AFM 图像表明，在纯水中制备的单组分 MUS SAM 具有随机的表面结构。相比之下，在水-乙醇混合溶剂中制备的 MUS SAM 显示出具有平躺构象的周期性条纹结构。结果表明，溶剂对长链磺酸酯 SAMs 的分子尺度结构有显著影响。此外，我们研究了具有相同链长的磺酸酯 MUS 和 11-巯基-1-十一醇（MUO）混合 SAM 的分子尺度结构。混合 SAM 的 FM-AFM 图像显示 MUS SAM 和 MUO SAM 域之间存在明显的相分离。在 MUO SAM 域中，掺入的 MUS 分子表现为突起。本研究的结果为长链磺酸酯和混合 SAM 提供了直接的结构信息。
