基于分子动力学的氧化石墨烯拉伸断裂行为与力学性能研究

与石墨烯相比,氧化石墨烯(graphene oxide, GO)的亲水性、分散性和反应活性更好,更易于作为增强材料而研发生成性能超常的复合材料,但另一方面,由于其电子结构较为复杂,致使目前有关力学方面的研究存在一定差异.本文利用分子动力学方法,建立了羟基、羧基和环氧基等官能团随机分布的GO原子模型;通过单向拉伸模拟,分析了其断裂行为,结果表明,远离羟基和羧基的环氧基对断裂具有"诱导"作用,并从化学成键、体系能量和应力分布三个角度对其机理进行了阐释;此外,进一步研究了拉伸应力$\!$-$\!$-$\!$应变曲线、极限强度、极限应变等力学性能与含氧官能团覆盖度间的关系,结果表明,极限强度、极限应变均随含氧官能团覆盖度的增大而呈减小趋势.分析认为,主要原因是官能团的出现对石墨烯面内的sp$^{2}$杂化形式造成了破坏,进而使得原子间键合能弱化,随着含氧官能团的覆盖度的增大,被弱化的键合能的数量和程度将越大,从而使得GO的极限强度、极限应变等越低. 研究结果可为GO的基础研究和工程应用提供参考. 

STUDY ON TENSILE FRACTURE BEHAVIOR AND MECHANICAL PROPERTIES OF GO BASED ON MOLECULAR DYNAMICS METHOD1)

In comparison with graphene, the graphene oxide (GO) has better hydrophilicity, dispersion performance and reaction activity, which makes it easier to interact with other materials to form composites with excellent properties. But on the other hand, due to the complexity of the electronic structure of the GO, there are some differences in the research of mechanics of GO at present. For this purpose, in the present paper, a random distribution model of GO containing the hydroxyl groups,epoxy groups and carboxyl groups was established based on the molecular dynamics method. And then, the tensile fracture behavior was analyzed by uniaxial tensile numerical simulation. The results illustrated that the epoxy groups which are far away from hydroxyl and carboxyl groups had induce effect on the fracture of GO. In addition, the mechanisms were explained from three aspects,which are the chemical bonding, system energy and stress distribution. Additionally, the influence of the coverage of oxygen-containing functional groups of hydroxyl groups, epoxy groups and carboxyl groups on the stress-strain curve, ultimate strength and ultimate strain of GO were further studied. The results showed that the ultimate strength and ultimate strain of GO decreased with the increase of the coverage of oxygen-containing functional groups of hydroxyl groups,epoxy groups and carboxyl groups. According to the analysis, the main reason is that the oxygen-containing functional groups of hydroxyl groups, epoxy groups and carboxyl groups destroy the sp$^{2}$hybrid form in the original graphene surface, thus weakening the bonding energy between atoms. Thereby, The greater the coverage of the oxygen-containing functional groups of hydroxyl groups, epoxy groups and carboxyl groups, the greater the amount and degree of weakened bonding energy, and the lower the ultimate strength of GO. The research results have certain reference value and significance for engineering application and basic research of GO.