Molecular Insight into the Toughness of Polyureas: A Hybrid All-Atom/Coarse-Grained Molecular Dynamics Study

Polyureas are known for their remarkable toughness, which originates from the nanoscale segregated morphology and hydrogen bonding between urea groups. However, the underlying molecular mechanism of how the microscopic structure results in the macroscopic toughness is not fully understood. In this work, the mechanical response and microstructural evolution of a model polyurea under uniaxial deformation were investigated via nonequilibrium molecular dynamics simulations based on a hybrid all-atom/coarse-grained model. The stress–strain curve obtained from the simulation captured the key features of the nonlinear mechanical response of polyureas. The structural evolution was characterized by the microscopic strain and stress as well as statistics of the hard-domain structure and segment conformations. Two distinct molecular mechanisms were identified: self-reinforcement by oriented hard segments and stress-adaptive release of soft segments. Through these mechanisms, the evolution of microscopic structure was related to the macroscopic toughening of polyureas, shedding light on the development of better materials.