### 石墨烯在甘油/尿素剥离液中的稳定行为的分子动力学模拟研究

1. a 武汉理工大学材料科学与工程学院 武汉 430070
b 武汉理工大学材料基因工程研究中心 武汉 430070
c 重庆国际复合材料股份有限公司 重庆 400082
• 投稿日期:2020-10-13 发布日期:2021-02-22
• 通讯作者: 李蓓
• 基金资助:
国家自然科学基金青年基金(51603160)

### Molecular Dynamics Simulation of the Stability Behavior of Graphene in Glycerol/Urea Solvents in Liquid-Phase Exfoliation

Chang-An Liua,b, Shi-Bo Hongc, Bei Lia,b,*()

1. a School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China
b Research Center for Materials Genome Engineering, Wuhan University of Technology, Wuhan 430070, China
c Chongqing Polycomp International Corporation, Chongqing 400082, China
• Received:2020-10-13 Published:2021-02-22
• Contact: Bei Li
• About author:
• Supported by:
National Natural Science Foundation of China(51603160)

Understanding of interfacial structure and stabilization mechanism of graphene sheets in green solvents during liquid-phase exfoliation is of great importance in advancing preparation, characterization and synthesis of graphene-based materials. However, it is difficult to monitor structural evolution of graphene in solvents using current available experimental techniques, and the resulting graphene stabilization mechanism has not been fully understood. In this work, molecular dynamics simulations are performed to investigate the structural evolution and stability behavior of the graphene sheets with different states in the glycerol/urea green solvents with varying concentrations. The results show that only the pristine graphene sheet at an initial interlayer spacing of 0.6 nm in the glycerol solvent restacks back and stays close to each other at a separation close to the intrinsic thickness of graphene. This is due to the fact that the glycerol molecules fail to diffuse into the graphene interlayer, and they could not afford a sufficient repulsive barrier to hinder the graphene aggregation. While in other pristine cases, a single- or double-layer solvent structure is formed and the interlayer separation is maintained at 0.65 nm or 1.12~1.18 nm, offering an efficient dispersion medium to stabilize the graphene sheets. Although the pristine multilayer graphene sheets present similar stability in different glycerol/urea solvents, the U-type graphene experiences distinct levels of stabilization in solvents in the order of pure glycerol>glycerol/urea(2/1)>glycerol/urea(3/1)>glycerol/urea(1/1), signifying that the shifted and exfoliated state of the graphene sheets plays an important role in the stabilization during liquid-phase exfoliation. Moreover, in the glycerol/urea binary solvents, the small urea molecules firstly diffuse into the graphene interlayer due to their strong π-π interaction with graphene, acting as a “dispersion initiator”. And then the glycerol molecules could have the chance to diffuse around or insert into the graphene interlayer to assist in stabilizing the graphene due to the hydrogen bonding between urea and glycerol. In this way, the glycerol helps to further increase the interlayer separation leading to a more stable dispersion, acting as a “dispersion co-stabilizer”. The formation of the confined urea and glycerol solvents thus provides a stable molecular layer structure between the graphene interlayer, enabling to stabilize the exfoliated graphene sheets effectively. As such, the findings in this work are believed to provide the atomic/molecular scale understanding of the stability behavior of the graphene sheets in glycerol/urea binary solvents during liquid-phase exfoliation.