Mechanistic Insights Into Polymer-Assisted Graphene Exfoliation: The Roles of Velocity, Adhesion, Cohesion, Temperature, Peeling Mode, and Edge Defect via Coarse-Grained Molecular Dynamics

Graphene exfoliation is a critical step in the fabrication of high-quality graphene layers. However, the underlying fracture mechanisms remain poorly understood. In this work, I employed coarse-grained (CG) molecular dynamics (MD) simulations to investigate how factors such as interfacial binding energy, substrate cohesion, temperature, peeling mode, and edge defects influence the outcome of the exfoliation process. To model polymer-assisted mechanical exfoliation, I used a finite-size system in which multilayer graphene (MLG) is sandwiched between two thin polymer films. Leveraging the spatiotemporal efficiency of the CG model, I performed fifty simulation iterations per parameter set and analyzed the results from a probabilistic perspective. The simulation results reveal that interfacial adhesion plays a pivotal role in determining exfoliation failure modes—governing whether the failure occurs through adhesive separation at the polymer–graphene interface or through successful exfoliation of graphene layers. At low interfacial binding energies, adhesive failure is predominant. As the interfacial binding energy increases, the failure mode shifts toward layer separation within MLG. A sharp transition zone exists between these regimes, where the probability of exfoliating different numbers of graphene layers becomes highly sensitive to interfacial adhesion strength. Additionally, I found that temperature, substrate adhesion, and peeling mode can modulate this transition. Notably, corner peeling introduces greater localized stress compared to side peeling, enabling monolayer exfoliation under conditions where interfacial and cohesive energies are comparable. To further investigate the role of edge defects, I modified the CGMD model by introducing edge cracks in MLG, which was treated as a stand-alone system. By systematically varying the crack length and model dimensions, I found that longer edge cracks significantly reduce the exfoliation force required for layer separation, while shorter cracks demand higher forces to initiate fracture. These results suggest that edge crack defects can be deliberately engineered to improve exfoliation efficiency and enable higher control over the location and propagation of fractures. Overall, this thesis provides new insights into the underlying mechanics of graphene exfoliation, establishing a computational modeling-based probabilistic framework for predicting failure modes. The findings demonstrate how interfacial adhesion, peeling configuration, and defect engineering can be strategically manipulated to optimize exfoliation outcomes and facilitate the reliable production of high-quality graphene for a wide range of advanced applications.