Deformation Mechanism of Mechanochromic Polymer Nanocomposites Fabricated by Self-Assembly of Colloidal Particles

A novel polymer nanocomposite consisting of polymer-grafted nanoparticles have attracted great attention due to their properties of self-assembling to an ordered colloidal crystal structure. However, the deformation mechanism of this colloidal crystal has not been clarified yet. In this study, the structural evolution of a colloidal crystal with rubbery/glassy block copolymer-grafted silica particles (BCP-g-SiO₂) was investigated by in situ ultra small-angle X-ray scattering (USAXS) under deformation. Poly(butyl acrylate) (PBA) and poly (methyl methacrylate) (PMMA) were chosen as inner and outer layers of BCP-g-SiO₂, respectively.
The heat-pressed film consisting of BCP-g-SiO₂ exhibited structural color due to the formation of photonic colloidal structure. The color changed under uniaxial stretching. The first order ring of USAXS pattern changed from circle to ellipsoid under elongation, indicating the lattice distance increased along the elongation direction but decreased in the direction perpendicular to elongation. Moreover, the BCP-g-SiO₂ with higher PBA ratio had larger transverse strain which was calculated from the d-spacing of the first order ring of structure factor, because the polymer layer was compressed more in the transverse direction under uniaxial stretching.