Molecular dynamics simulation study of the joining strength of different polymer-aluminum heterointerfaces in nano-injection molding

Nano-injection molding has been widely used in polymer-metal integrated structures. This study aimed to investigate the joining strength and bonding mechanism between polymer-metal interfaces, as well as the interfacial interactions and joining properties with molecular dynamics methods. Besides, six polymer-aluminum interface systems in 5.4 x 5.4 x 12.5 nm cuboids composed of aluminum, polymer, and vacuum layers (from bottom to top) were constructed. The joining strength and flow behavior were explored by calculating the interfacial energy, filling rate, gyration radius, and pullout force. The effects of nano-cavity shape and non-bonding interaction strength on the separation process were analyzed. The simulation results demonstrated that during the filling process, the polymer molecular chains slipped and flowed along the inner wall of the nano-cavity, and the filling behavior depended largely on the fluidity and filling rate of the polymer. During the separation process, the polymer chains close to the aluminum matrix were stretched, the polymer chains far from the interface were relatively stable, and residual polymer molecular chains were observed near the interface. The interface joining primarily contributed to the interaction energy. Additionally, the formed mechanical interlocking effect further enhanced the joining strength when the nano-cavity was in a "T" shape, providing a reference value for the nano-injection time and dwell time.