Aggregation of Graphene Flakes Under Electric Field: A Molecular Simulation Study.

Graphene flakes, as two-dimensional materials, can self-assemble under certain conditions and have wide-ranging applications in industries from electronics to biomedicine due to their exceptional mechanical, thermal, and electrical properties. Recent studies indicate that single graphene flakes can be aligned by an external electric field (EF) in polar solvents like water. However, how their self-assembly behavior is influenced by the EF remains unclear. In this work, we use molecular dynamics (MD) simulations to explore the self-assembly of graphene flakes with different shapes and sizes under various EF conditions: static EF (SEF), alternating EF (AEF), and circularly polarized EF (CPEF). Our results reveal that different EF conditions significantly impact the number of pairwise bindings between flakes and the average size of the aggregates. In the absence of an EF, graphene flakes tend to form globular, round-like structures. When an EF is applied, particularly under SEF, the aggregates adopt a stretched configuration aligned with the field's direction, while AEF has a weaker alignment ability than SEF. Under CPEF, elongated aggregates rotate, following the field with a characteristic lag angle. Furthermore, while aggregates can explore more configurations under CPEF, the two-dimensional free energy landscape indicates that the stretched state is the most stable. This work deepens our understanding of how EFs influence the self-assembly of graphene flakes, potentially guiding future engineering applications for controlling the aggregation of graphene and other discotic molecules.