Probing High Pressure Structural Evolution in Polyurea with in situ Energy Dispersive X-Ray Diffraction and Molecular Dynamics Simulations*

Polyurea has been proven as an effective coating in defense applications due to its unique mechanical properties. To gain a more complete understanding of the high-pressure atomic-level morphology of these phases and to validate molecular dynamics (MD) simulations, multi-angle energy dispersive x-ray diffraction experiments were performed in situ up to pressures ~6 GPa at room and elevated temperatures. Structure factors were obtained and compared to MD simulations with an average error of less than 5% between major peak positions at room temperature, which indicated that the first sharp diffraction peak shifted from 4.56 Å to lower d-spacing with pressure, indicating compression between hard segments. This was further supported by the behavior of a peak at ~3.86 Å from the pair distribution function, suspected to represent π-stacking and separation between soft segments. Compression within hard domains themselves is minimal at room temperature.