Polymer-metal hybrid structures have attracted significant attention recently due to their advantage of great weight reduction and excellent integrated physical/chemical properties. However, due to great physicochemical differences between polymers and metals, obtaining an interface with high bonding strength is a challenge, which makes it critically important to clarify the underlying bonding mechanisms. In the present research, we focused on revealing the underlying bonding mechanisms of a laminated Cr-coated steel-ethylene acrylic acid (EAA) strip prepared by hot roll bonding from the microscale to the molecular scale with experimental evidence. The microscale mechanical interlocking was analyzed and proven by scanning white light interferometry and scanning electron microscopy (SEM) by means of observing the surface and cross-sectional morphologies. Additionally, interfacial phases and chemical compositions were analyzed by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). More directly and effectively, the interface was successfully exposed for X-ray photoelectron spectroscopy (XPS) analysis. Combined with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and depth profiling analysis, the formation of -(O═)C-O-Cr and -C-(O-Cr)2 covalent bonds through chemical reactions at the interface between -COOH and Cr2O3 was verified. Based on these characterization results, interfacial bonding mechanisms for the laminated Cr-coated steel-EAA strip were clearly identified to be chemical bonding and micromechanical interlocking, along with hydrogen bonding, which were all demonstrated with solid experimental evidence. In addition, 3D-render view and cross-section images of typical ion fragments at the interface were used to reveal the interfacial structure more comprehensively. The contributions of hydrogen bonds and covalent bonds to the interface were evaluated and compared for the first time. This study provides both methodological and theoretical guidance for investigating and understanding interfacial bonding formation in polymer-metal hybrid structures.

Chemical Reaction and Bonding Mechanism at the Polymer-Metal Interface.

Polyphenylene sulfide (PPS) and copper (Cu) were selected as candidate materials for modeling a nano-injection molding process. Four nanopit shapes (rectangular, cylindrical, pyramidal and conical)...

MD simulation analysis of the anchoring behavior of injection-molded nanopits on polyphenylene sulfide/Cu interface

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 × 5.4 × 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. 

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

The dependence between the conformation of polystyrene (PS) and its molecular weight (Mw) in the vicinity of a metal interface was investigated by sum frequency generation (SFG) spectroscopy. Tilt angles θ ≥ 50° (the angle between the C2 axis of the pendant phenyl ring and the surface normal) were observed for all samples because of the interaction between the aromatic rings and the metal surface. Furthermore, it was found that θ decreases with increasing Mw for PS samples ranging from 20 × 103 g/mol to 400 × 103 g/mol. The intensity of the backbone SFG signal was higher for high Mw PS, compared to low Mw PS, indicating a greater number of backbone interactions with the silver substrate surface for the high Mw sample. These structural differences are driven by different entropic and enthalpic contributions to the free energy of adsorption for different polymer molecular weights. Differences in the polymer free volume and in the relative amount of chain ends with higher mobility may also influence the chain conformation. These results suggest that important interfacial properties of polymeric thin films, such as adhesion and wettability, could be tailored by modifying the polymer Mw to achieve the desired interfacial conformation.

Influence of Polymer Molecular Weight on Chain Conformation at the Polystyrene/Silver Interface.

Experimental investigation and molecular dynamics simulations of the effect of processing parameters on the filling quality of injection-molded micropillars

Donglei Liu

Papers

Study on the interfacial interactions and adhesion behaviors of various polymer‐metal interfaces in nano molding

MD simulation analysis of the anchoring behavior of injection-molded nanopits on polyphenylene sulfide/Cu interface