Mechanical approaches to dynamic, reversible mechanochromism based on thin film interference

Abstract

Mechanochromic materials have received considerable attentions due to their potential applications in structural health monitoring, finger printing, stretchable electronics, and soft robotics. Herein we present a new strategy for polymeric mechanochromism by synergistic integration of mechanical engineering with thin film interference. This new strategy enables scalable and affordable manufacturing of mechanochromic polymeric systems that exhibit dynamically reversible mechanochromic properties with high sensitivity to smaller strains (0–60%) without the requirement of external ultraviolet light sources. We show that the mechanicanochromic properties can be tailored by using different mechanical approaches. In our kirigami approach via cutting, the coupling of buckling-induced kirigami and viewing angle-dependent interference color leads to unique anisotropic, load direction-dependent mechanochromism. In our tunable reflectivity shield approach via cracking, the polymer-metal bilayer film is used as a mechanically tunable shield to program its interference reflection color intensity and the visibility of the underlying dyed elastomeric substrate layer. The coupling of strain-dependent polymer-metal cracking and tunable reflection and transmission of the interference coloration film yields isotropic, load direction-independent mechanochromism.