Fabrication and Deformation of Mechanochromic Nanocomposite Elastomers Based on Rubbery and Glassy Block Copolymer-Grafted Silica Nanoparticles

The strength of silica-based mechanochromic nano-composites was improved by a novel nanocomposite synthesized by grafting poly(butyl acrylate) (PBA)-b-poly(methyl methacrylate) (PMMA) from silica nanoparticles (SiNP). Samples with different PMMA/PBA ratios were prepared to clarify the effect of the rubbery/glassy block copolymer ratios on the mechanical properties of the nanocomposites. The nanocomposites formed a face-centered cubic paracrystal-like structure and exhibited structural color. Time-resolved ultrasmall-angle X-ray scattering was carried out to investigate the structural evolution of the nanocomposites by uniaxial and biaxial mechanical deformation. Changes in color and mechanochromic properties were observed at varying distances between the particles by mechanical deformation. The nanocomposites exhibited elastic and plastic properties and became more rubber-like as the rubbery PBA weight ratio increased. The polymer brush deformed into a prolate spheroid by uniaxial stretching, and the distance between SiNP decreased in the direction perpendicular to elongation, which resulted in the color change by mechanical deformation. Moreover, the distance between SiNP increased isotropically by biaxial stretching. The polymer brush was elongated isotropically toward the in-plane direction and deformed into an oblate spheroid.