Department of Physics, Lancaster University , Lancaster LA1 4YB, U.K.
Materials Science Institute, Lancaster University , Lancaster LA1 4YW, U.K.
ACS Nano. 2017 Mar 28;11(3):3404-3412. doi: 10.1021/acsnano.7b01071. Epub 2017 Mar 15.
Graphene and related two-dimensional (2D) materials possess outstanding electronic and mechanical properties, chemical stability, and high surface area. However, to realize graphene's potential for a range of applications in materials science and nanotechnology there is a need to understand and control the interaction of graphene with tailored high-performance surfactants designed to facilitate the preparation, manipulation, and functionalization of new graphene systems. Here we report a combined experimental and theoretical study of the surface structure and dynamics on graphene of pyrene-oligoethylene glycol (OEG) -based surfactants, which have previously been shown to disperse carbon nanotubes in water. Molecular self-assembly of the surfactants on graphitic surfaces is experimentally monitored and optimized using a graphene coated quartz crystal microbalance in ambient and vacuum environments. Real-space nanoscale resolution nanomechanical and topographical mapping of submonolayer surfactant coverage, using ultrasonic and atomic force microscopies both in ambient and ultrahigh vacuum, reveals complex, multilength-scale self-assembled structures. Molecular dynamics simulations show that at the nanoscale these structures, on atomically flat graphitic surfaces, are dependent upon the surfactant OEG chain length and are predicted to display a previously unseen class of 2D self-arranged "starfish" micelles (2DSMs). While three-dimensional micelles are well-known for their widespread uses ranging from microreactors to drug-delivery vehicles, these 2DSMs possess the highly desirable and tunable characteristics of high surface affinity coupled with unimpeded mobility, opening up strategies for processing and functionalizing 2D materials.
石墨烯和相关的二维（2D）材料具有出色的电子和机械性能、化学稳定性以及高表面积。然而，为了实现石墨烯在材料科学和纳米技术中的一系列应用潜力，我们需要了解和控制石墨烯与定制的高性能表面活性剂的相互作用，这些表面活性剂旨在促进新的石墨烯系统的制备、操作和功能化。在这里，我们报告了对基于芘-聚乙二醇（OEG）的表面活性剂在石墨烯表面的结构和动力学的综合实验和理论研究，这些表面活性剂先前已被证明可在水中分散碳纳米管。使用涂覆有石墨烯的石英晶体微天平在环境和真空环境中实验监测和优化表面活性剂在石墨表面上的分子自组装。使用超声和原子力显微镜在环境和超高真空下对亚单层表面活性剂覆盖层的纳米尺度分辨率纳米力学和形貌进行映射，揭示了复杂的、多长度尺度的自组装结构。分子动力学模拟表明，在纳米尺度上，这些结构在原子级平坦的石墨表面上取决于表面活性剂的 OEG 链长，并且预计会显示出以前未见的二维自组装“海星”胶束（2DSM）类。虽然三维胶束因其在微反应器到药物输送载体等广泛应用而广为人知，但这些 2DSM 具有高表面亲和力和无阻移动性的高度理想和可调特性，为二维材料的加工和功能化开辟了策略。
