Polyimide Two-Wave Structure Produced by Shock Compression

Polymeric materials undergo densification when dynamically compressed, transitioning the polymer from reactants to products. During gas gun-driven planar impact, we can observe this decomposition with velocimetry probes capturing the particle velocity (movement of the material) history that results from the impinging shock wave. This transition produces a shock wave for both the reactants and the products. If the volume change is large enough, the reactants wave will separate from products wave, generating a two-wave structure in the velocimetry profiles. If the polymer is shocked above or below this transition region, a single wave will be observed. Polyimide (PI) is composed of imide monomer units (-OC₂-NC-C₂O-); it is used as a thermoplastic for high pressure, high temperature applications. Understanding how this polymer reacts within its transition region (17.8-30 GPa) provides vital information for equation of state (EOS) modeling. PI has a large volume change, 20.3%, when shocked into its transition region. Through gas gun-driven planar impact we have observed a two-wave structure in PI with velocimetry probes. The two-wave structure measurement provides kinetic parameters for the reactants-to-products transition that informs the kinetics for EOS models.