Solvent-Free Shear-Induced Assembly of Polymer-Grafted Silica Particles into Thermoplastic Colloidal Crystals

Solvent-free preparation of colloidal crystals (CCs) remains challenging because conventional approaches typically rely on particle dispersions in liquid media. Here we report a rational strategy for preparing well-ordered CC films by direct shear treatment of bulk particles without solvent. Silica particles (SiPs) are surface-modified with well-defined poly(n-butyl acrylate) (PBA) chains synthesized by atom transfer radical polymerization (ATRP). At 150 °C, thermoplastic softening of the PBA chains leads to a disentangled polymer network, allowing the PBA-grafted SiPs to be directly sheared without the need for a dispersion medium. Direct shear treatment at 150 °C induces the rearrangement of SiPs into well-ordered CC assemblages, leading to significant enhancement of visible reflectance. Such intensified light reflection can be retained even after cooling to 20 °C by the thermoplasticity of grafted PBA chains. Moreover, the reflection colors of well-organized CC films are finely tuned by controlling the molecular weight of grafted PBA chains through ATRP.