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 andhydrogen bonding between urea groups. However, the underlyingmolecular mechanism of how the microscopic structure results in themacroscopic toughness is not fully understood. In this work, themechanical response and microstructural evolution of a modelpolyurea under uniaxial deformation were investigated via non-equilibrium molecular dynamics simulations based on a hybrid all-atom/coarse-grained model. The stress-strain curve obtained fromthe simulation captured the key features of the nonlinear mechanicalresponse 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 orientedhard segments and stress-adaptive release of soft segments. Through these mechanisms, the evolution of microscopic structure wasrelated to the macroscopic toughening of polyureas, shedding light on the development of better materials.