Self-defending anti-vandalism surfaces based on mechanically triggered mixing of reactants in polymer foils
The bombardier beetle uses attack-triggered mixing of reactants (hydrochinone, hydrogen peroxide (H2O2) and enzymes as catalysts) to defend itself against predators. Using multi-layer polymer sheets with H2O2 and catalyst (MnO2) filled compartments we developed a 2D analogous bio-inspired chemical defence mechanism for anti-vandalism applications. The reactants were separated by a brittle layer that ruptures upon mechanical attack and converts the mechanical energy trigger (usually a few Joules) into a chemical self-defence reaction involving release of steam, and optionally persistent dyes and a DNA-based marker for forensics. These surfaces effectively translate a weak mechanical trigger into an energetic chemical reaction with energy amplification of several orders of magnitude. Since the responsive materials presented here do not depend on electricity, they may provide a cost effective alternative to currently used safety systems in the public domain, automatic teller machines and protection of money transport systems. Anti-feeding protection in forestry or agriculture may similarly profit from such mechanically triggered chemical self-defending polymer surfaces.