Unravelling the Behaviour of Brush Block Nanocomposites at Ultrahigh Strain Rates*

Poly(tert-butyl acrylate)-block-polyethylene oxide (PtBA-b-PEO) brush block (BB) copolymers offer rapid self-assembly kinetics and ready access to long-range order. Taking advantage of cooperative self-assembly using hydrogen bonding additives, we incorporate phenol formaldehyde (Resol) resins into the PEO block to create a crosslinked network, and thus enable formation of alternating soft (PtBA) and hard (Resol crosslinked) multi-layered films. We then explore ultrahigh strain rate behaviour (>10⁶ s^-1) of these BB nanocomposites films using Laser Induced Projectile Impact Test (LIPIT). Rigid spherical alumina particles of 15-25 µm in diameter are accelerated towards these composites with velocities ranging from 50 to 450 m/s and the corresponding impact and residual flight paths are captured by ultrafast stroboscopic imaging with exposure times of less than 1 ps. We analyse the change in kinetic energies, the deformation depth as measured by profilometry, and scanning electron microscopy images to interpret real-time deformation propagation across the BB nanocomposite.