Self-Assembly Dynamics and Stability through Concentration Control at the Solution/HOPG Interface
Self-Assembly Dynamics and Stability through Concentration Control at the Solution/HOPG Interface
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DOI：
10.1021/acs.jpcc.2c03766
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发表时间：
2022-07
期刊：
影响因子：
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通讯作者：
Kirill Gurdumov;U. Mazur;K. W. Hipps
中科院分区：
文献类型：
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作者：
Kirill Gurdumov;U. Mazur;K. W. Hipps
了解自组装单分子膜（SAMs）的形成动力学和热力学提供了对分子尺度上分子间力的微妙平衡的洞察。我们在这里调查的增长，动力学和稳定性的模型非共价自组装，钴（II）octagethylephyrin，在溶液HOPG接口。通过扫描隧道显微镜（STM）捕获并研究了自组装层的成核和生长的实时成像，并使用计算方法进一步探索。一个定制的STM溶液流动池的设计和实施，以允许在非常低的浓度和挥发性溶剂的自组装原位监测。低浓度下的流动研究提供了对形成的自组装膜的早期形成动力学和结构的深入了解。结果发现，有机溶剂的选择在SAM的动力学和结构中起着显着的作用。这些结果，反过来，提供洞察驱动自组装的分子间力的平衡。在1，2，4-三氯苯的情况下，溶剂的作用特别强。在TCB下，形成非常稳定的矩形结构，并通过溶剂掺入而稳定。过渡到无溶剂的假六方结构，只有观察到卟啉是在近溶解度极限浓度。当以甲苯、正癸烷和1-苯基辛烷为溶剂时，卟啉吸附层中只有准六方结构。混合溶剂的竞争进行了测试，并提供了进一步的洞察溶剂的作用，在自组装的热力学和动力学。
Understanding the formation kinetics and thermodynamics of self-assembled monolayers (SAMs) provides an insight into the delicate balance of intermolecular forces on the molecular scale. We herein investigate the growth, dynamics, and stability of a model noncovalent self-assembler, Co(II) octaethylporphyrin, at the solution–HOPG interface. Real-time imaging of the nucleation and growth of the self-assembled layer was captured and studied via scanning tunneling microscopy (STM) and further explored using computational methods. A custom STM solution flow cell was designed and implemented to allow for in situ monitoring of self-assembly at very low concentrations and with volatile solvents. Flow studies at low concentration provide an insight into early-stage formation kinetics and structure of the SAMs formed. It was found that the choice of organic solvent plays a dramatic role in the kinetics and structure of the SAM. These results, in turn, provide insight into the balance of the intermolecular forces driving the self-assembly. The role of the solvent was particularly strong in the case of 1,2,4-trichlorobenzene (TCB). Under TCB, a very stable rectangular structure is formed and stabilized by solvent incorporation. A transition to a solvent-free pseudo-hexagonal structure was only observed when the porphyrin was at near-solubility limit concentrations. Only the pseudo-hexagonal structure was observed in the porphyrin adlayer when toluene, decane, and 1-phenyloctane were used as solvents. Mixed solvent competition was tested and gave further insight into the role solvent plays in the thermodynamics and kinetics of self-assembly.