Cai Lu, Hou Sensheng, Wei Xiangyu, Tan Guangsu, Peng Zhengwei, Yan Yujiao, Wang Lei, Lei De, Wu Yanguang, Liu Zhitian
School of Materials Science and Engineering, Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, Wuhan Institute of Technology, Wuhan 430205, Hubei, P. R. China.
School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China.
Phys Chem Chem Phys. 2020 Jan 28;22(4):2061-2072. doi: 10.1039/c9cp05924e. Epub 2020 Jan 6.
CO expanded organic solvents possess significant advantages in liquid-phase exfoliation to obtain monolayer/few-layer graphene from graphite. Further insights into the mechanism of graphene exfoliation in such solvents are essential to explore liquid-phase dispersion of graphene as a more potent alternative to chemical vapor deposition. In this study, dynamic processes of exfoliation and stabilization of graphene in CO-N,N-dimethylformamide (DMF), CO-N-methylpyrrolidone (NMP), CO-dimethyl sulfoxide (DMSO), and CO-ethanol (EtOH) were investigated using molecular dynamics simulations. The origin of the effect of each solvent on graphene exfoliation was analyzed quantitatively through potential mean force simulations. It has been found that the organic solvent in a CO expanded solvent should be chosen with proper surface tension, and there exist two different graphene exfoliation processes in the effective solvents, which can be described as "burger dissociation" and "extrusion-taking away" processes, respectively. In the former process, a characteristic "super-burger-like" conformation with a semi-exfoliated structure was formed, which was the deciding factor to obtain high ratio of monolayer/few-layer graphene in dispersion product. A theoretical explanation has also been provided at the molecular level to the earlier experimental phenomena. A predicted simulation of the CO-3,3'-iminobis(N,N-dimethylpropylamine) (DMPA) system is also calculated. This investigation helps to avoid incompatible CO expanded organic solvents employed in the experimental studies and provides theoretical clues to understand the mechanism of exfoliation and stabilization of graphene in such solvents.
在从石墨中获得单层/少层石墨烯的液相剥离过程中，CO膨胀有机溶剂具有显著优势。进一步深入了解石墨烯在这类溶剂中的剥离机制，对于探索石墨烯的液相分散体作为化学气相沉积更有效的替代方法至关重要。在本研究中，利用分子动力学模拟研究了石墨烯在CO-N,N-二甲基甲酰胺（DMF）、CO-N-甲基吡咯烷酮（NMP）、CO-二甲基亚砜（DMSO）和CO-乙醇（EtOH）中的动态剥离和稳定过程。通过势能平均力模拟定量分析了每种溶剂对石墨烯剥离作用的起源。研究发现，CO膨胀溶剂中的有机溶剂应选择具有适当表面张力的，并且在有效溶剂中存在两种不同的石墨烯剥离过程，分别可描述为“汉堡解离”和“挤出带走”过程。在前一个过程中，形成了具有半剥离结构的特征性“超级汉堡状”构象，这是在分散产物中获得高比例单层/少层石墨烯的决定性因素。还在分子水平上对早期实验现象提供了理论解释。还计算了CO-3,3'-亚氨基双（N,N-二甲基丙胺）（DMPA）体系的预测模拟。这项研究有助于避免实验研究中使用不相容的CO膨胀有机溶剂，并为理解石墨烯在这类溶剂中的剥离和稳定机制提供理论线索。
