Tuning high-strain rate deformation of self-assembled block copolymers

The mechanical behavior of materials at high strain rates and at small length scales is often surprising and has attracted significant attention across the materials community. The laser-induced projectile impact test (LIPIT) can be used to investigate the various deformation mechanisms and kinetic energy absorption characteristics during impact using a hard sphere to perforate a thin polymer specimen-target as well as impacting a polymer specimen-sphere into a rigid substrate. A self-assembled poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) block copolymer (BCP) thin films consist of alternating in-plane lamellar layers. LIPIT allows launching of micron-scale silica projectiles at an incident velocity of over 300 m/s toward free-standing BCP films, producing extreme strain rates of ~10⁷ s^-1. The P2VP layers can be selectively swollen by ionic salts or ionic liquids. Pristine and swollen BCPs exhibit very different deformation morphologies and specific penetration energies due to the differences in the interaction between swelling agents and P2VP, such as the shape of radial and tangential crazes and the surface wrinkle, after impact.