Rheological Characterization of Adhesive Reassembly: Impact of Dynamic Covalent Bonds on Viscosity

A vulcanization analyzer was employed to investigate the flow properties of adhesives during the reassembly process by monitoring the variation in torque over time at a constant temperature. The data, as illustrated in Figure 6, reveal a distinct pattern. Initially, the torque experiences a rapid increase due to the contact between the adhesive and the rotating plate. Subsequently, the torque rapidly decreases as the adhesive softens under the influence of heat. The thermal dissociation of Diels-Alder bonds within the adhesive leads to a gradual collapse of the cross-linked network, resulting in a transformation into a linear molecular chain structure. This structural change manifests as a continued decrease in torque until it stabilizes. Recognizing that torque is a proxy for viscosity, these findings indicate that the viscosity of the cross-linked network topology can decrease significantly during rearrangement at elevated temperatures, facilitating the reassembly of adhesives. This phenomenon is attributed to the reversible nature of the dynamic covalent bonds, which break upon heating, thereby altering the adhesive's rheological properties.