"Effect of graphene oxide with different oxidation degrees on mechanical properties of styrene-butadiene rubber: Experiment and molecular simulation"

Graphene oxide (GO) has proven to be an effective reinfor-cing filler for rubber［1］. GO has superior mechanical properties, barrier properties, large specific surface area and abundant oxygen-containing functional groups［2］. However, the change in the oxidation degree of GO has a great effect on its chemical properties, the interaction between GO and the matrix, and the dispersion uniformity in the rubber matrix, which has a great effect on the reinforcement of rubber［3］. Molecular dynamics (MD) simulation, as a novel, practical and powerful theoretical tool, has been used to obtain detailed information on interfacial interactions, and even provide a route for new designs of high-performance polymer nanocomposites. In this work, GO with different oxidation degrees was prepared and incorporated into styrene-butadiene rubber (SBR) to obtain GO/SBR composites. By combining experiment and MD simulation, the relationship between material microstructure and properties was explored at the molecular level. The typical formulation of rubber compounds was SBR 100 phr (in mass, the same below), GO 1.8 phr, 4010 NA 2.0 phr, zinc oxide 2.0 phr, stearic acid 2.4 phr, accelerator CZ 2.2 phr and sulfur 1.5 phr. The composite samples were named GO-x/SBR, where x represented the mass ratio of potassium permanganate/graphite. In MD simulation, binding energy (Ebinding) was calculated through Equation(1)［4］: Ebinding = -(Etotal-Efiller-Ematrix), (1) where, Etotal was total energy of the system; Efiller and Ematrix were energy of the filler and rubber matrix, respectively. The mechanical properties of GO-x/SBR nanocomposites were shown in Table 1. It was found that GO could effectively improve the mechanical properties of the SBR matrix. Tensile strength of GO-1.8/SBR nanocomposites was increased by 267%, indicating that GO with an appropriate oxidation degree could utilize π-π interactions between polar groups and SBR to increases the interfacial interaction sites and result in stress transfer［5］. The Ebinding calculated by MD simulation of GO/SBR nanocomposites was also shown in Table 1. The Ebinding of GO-1.8/SBR nanocomposites was the highest, indicating that GO-1.8 had the best compatibility with SBR. Combined with the mechanical properties results, the polarity of GO-1.8 was similar to that of SBR and the interfacial interaction was stronger, greatly improving the mechanical properties of SBR nanocomposites［6］.