Simulations with tens of millions of particles confirm the extraordinary mechanical reinforcement that a tiny amount of graphene can provide when doped with an ordinary plastic material.
Since its synthesis almost two decades ago, graphene has amazed us with its extraordinary mechanical properties: in principle, these completely two-dimensional carbon layers are five times stiffer than the most reinforced steel and 150 times stronger! The problem is that it is not easy to exploit these extraordinary properties because the graphene sheets cannot be used alone due to their extremely thin thickness (the size of an atom!). They must be incorporated into a matrix, such as a polymer, in a controlled manner, which presents a number of problems in terms of synthesis, structure and resistance to mechanical fatigue.
Micrometric molecular digital model of a PVA/graphene nanocomposite consisting of 30,000,000 atoms for chemically realistic simulation of mechanical strengthening mechanisms at the interface.
© M. Vassaux.
The large-scale production of such innovative materials by effectively exploiting the properties of graphene remains an uncertain prospect to date. In polymer/graphene composites, understanding the force transfer mechanisms between the polymer matrix and the two-dimensional nanosheet remains one of the current frontiers.
In a recent work, a collaboration between researchers from University College London and the Institut de Physique de Rennes (IPR, CNRS / Université de Rennes) used chemically realistic and very large molecular simulations (up to 30 million particles, describing length scales down to) . micrometers) to explain the strengthening mechanisms of graphene-based nanocomposites.
The use of latest generation supercomputers (ARCHER2, EPCC, UK) has made it possible to realistically describe already characterized experimental systems by simulating the mechanical behavior of a graphene layer several micrometers long surrounded by a thermoplastic polymer matrix. The simulations thus confirmed a theory that has been established for more than 10 years (“two-dimensional shear delay theory”), which explains the mechanism by which a two-dimensional nanometric inclusion such as graphene can reinforce a polymer matrix.
Beyond a validation of the shear delay theory, the study shows that if graphene layers longer than 500 nm can significantly improve the elastic properties, it is essential for the efficiency of forced transfer that the waves of the layers are minimal. However, the synthesis conditions cause sheets to have curved, pleated or wrinkled shapes due to limitations or defects. According to the study, reducing these graphene waves would lead to a significant improvement in the mechanical properties of the composite.
The study therefore makes it possible to establish the geometric and physicochemical properties that must be taken into account in order to observe significant mechanical reinforcement through the incorporation of graphene. This contribution will help guide the synthesis of graphene nanosheets as well as their functionalization to optimize the industrialization of lightweight and high-performance nanocomposites. These results are published in the journal Advanced Materials.
References
Large-scale molecular dynamics explains the mechanics of reinforcement in graphene-based composites.
James L. Suter, Maxime Vassaux, Peter V. Coveney, Advanced Materials, published June 28, 2023.
doi: 10.1002/adma.202302237
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