Meso-scale computational investigation of polyurea microstructure and its role in shockwave attenuation/dispersion

In a number of recently published studies, it was demonstrated that polyurea possesses a high shockwave-mitigation capacity, i.e. an ability to attenuate and disperse shocks. Polyurea is a segmented thermoplastic elastomer which possesses a meso-scale segregated microstructure consisting of (high glass-transition temperature, T-g) hydrogen-bonded discrete hard domains and a (low T-g) contiguous soft matrix. Details of the polyurea microstructure (such as the extent of meso-segregation, morphology and the degree of short-range order and crystallinity within the hard domains) are all sensitive functions of the polyurea chemistry and its synthesis route. It has been widely accepted that the shockwave-mitigation capacity of polyurea is closely related to its meso-phase microstructure. However, it is not presently clear what microstructure-dependent phenomena and processes are responsible for the superior shockwave-mitigation capacity of this material. To help identify these phenomena and processes, meso-scale coarse-grained simulations of the formation of meso-segregated microstructure and its interaction with the shockwave is analyzed in the present work. It is found that shockwave-induced hard-domain densification makes an important contribution to the superior shockwave-mitigation capacity of polyurea, and that the extent of densification is a sensitive function of the polyurea soft-segment molecular weight. Specifically, the ability of release waves to capture and neutralize shockwaves has been found to depend strongly on the extent of shockwave-induced hard-domain densification.