Surface Relaxation Of Epoxy Vitrimer

Vitrimer has become the research frontier of high molecular materials due to its unique self-repair ability and repeatability.The study on the segment relaxation behavior will provide the theoretical basis and technical support for the molecular design and application of new Vitrimer materials.Furthermore,the surface segment relaxation behavior is important for self-healing,interface welding,and other applications involving Vitrimer surface properties.However,the current studies on the relaxation behavior of Vitrimer mostly focus on the bulk,and few studies pay attention to the relaxation behavior of its surface segments.In this paper,the surface relaxation behavior of epoxy Vitrimer film was studied by atomic force microscopy（AFM）by characterizing the change of surface roughness.the main results are as follows:（1）For epoxy Vitrimer films with the same composition,the degree of surface roughness decrease is positively correlated with annealing temperature and time.The rough surface of epoxy Vitrimer film relaxes at least 12℃below the bulk topological freezing transition temperature(T_v,bulk),and the activation energy of the surface of bond exchange reaction is much lower than that of bulk.As T_v is an important processing temperature parameter of Vitrimer,below this temperature,the bond exchange reaction slows down significantly.Therefore,this result indicates that the surface of epoxy Vitrimer may have faster bond exchange reaction kinetics or lower T_v than that of epoxy vitrimer.（2）For the epoxy Vitrimer films with different components,the species and concentration of catalyst have a decisive effect on the T_v,bulk of epoxy Vitrimer,but do not affect its glass transition temperature(T_g,bulk).The surface relaxation behavior of epoxy Vitrimer films is affected by both segment motion and dynamic exchange between molecules,where the surface relaxation controlled by the dynamic exchange reaction dominates,and the interaction between T_g and T_v further accelerates the surface relaxation of the samples.The existence of topological defects enlarges the difference between the sample surface and bulk relaxation behavior.