Probing High-Pressure Structural Evolution in Polyurea with In Situ Energy-Dispersive X-ray Diffraction and Molecular Dynamics Simulations

T Eastmond and J Hu and V Alizadeh and R Hrubiak and J Oswald and A Amirkhizi and P Peralta, MACROMOLECULES, 54, 597-608 (2021).

DOI: 10.1021/acs.macromol.0c02266

Polyurea, an elastomer with a phase-segregated microstructure, has been proven as an effective coating in defense applications. 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 of similar to 6 GPa at room temperature. Structure factors were obtained and compared to MD simulations with an average error of less than 5% between major peak positions. The first sharp diffraction peak shifted from 4.56 A to lower d-spacing with pressure, indicating compression between hard segments. This was further supported by the behavior of a peak at similar to 3.86 A from the pair distribution function (PDF), suspected to represent p-stacking and separation between soft segments. Compression within the hard segments themselves is minimal as low-r peaks in the PDF are not greatly affected by pressure.

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