Understanding the Nanoscale Deformation Mechanisms of Polyurea from In Situ AFM Tensile Experiments

Here, we report in situ AFM tapping-phase study of polyurea’s nano and mesoscale phase transitions within the submicron-size field of view. To this end, we designed and assembled a novel in situ AFM loading device that keeps a reference point stationery within the observation window. Using this device, we acquired sequential AFM-tapping-mode phase images of polyurea’s nanophase evolution during relaxation under various fixed tensile strains up to 200%. We found that initial hard nano-domains fragment upon rapid loading and the fragmented hard phases go through various nano and mesoscale phase transitions. These fragmented pieces are recombined to form coarsened bicontinuous clusters during the relaxation process. The AFM in situ testing enables us to better understand dynamic-bond characteristics of segmented block copolymers. Interplay between the dynamic-bond characteristics of supramolecular interactions and the hard/soft-phase load/deformation sharing characteristics is believed to predict the self-healing and dynamic toughening mechanisms of polyurea.