Multifunctional polymer colloidal microspheres for stimuli-responsive structural color coatings with intrinsic...

Stimuli-responsive structural color coatings based on photonic crystals (PCs) have attracted considerable research attention due to their potential as advanced and eco-friendly platforms for sensing and display. While current research is largely centered on achieving single-stimulus response or monofunctionality, the integration of multi-stimuli responsiveness and multi-functionality into a single structural coating remains a major challenge. Herein, we successfully synthesized novel multi-functional poly(methyl methacrylate-acrylic acid-[3-(methylacrylamide) propyl] trimethyl ammonium chloride) (PMAM) microspheres with a one-pot, soap-free emulsion polymerization strategy. A series of six distinct PMAM microsphere samples with uniform and tunable particle diameters was obtained by precisely adjusting the monomer mass ratio. Atomization deposition of these microspheres onto fabric substrates enabled the fabrication of vivid structural color coatings, yielding hues ranging from purple and blue to green, and light red. These structural color coatings demonstrated a fast (1-2 s) and reversible response to water, allowing precise monitoring of water content. Moreover, the carboxyl groups present on PMAM microspheres enabled distinct pH-dependent color changes, making these coatings applicable for non-invasive sweat pH sensing. Most notably, the cationic quaternary ammonium moieties of PMAM microspheres confer robust inherent antibacterial properties to these coatings, with inhibition efficiencies surpassing 96% for both E. coli and S. aureus. This work integrates structural color generation, dual (solvent/pH) responsiveness, and intrinsic antibacterial function into a single coating, offering a multifunctional platform that holds promise for next-generation wearable sensors in real-time physiological monitoring and personal hygiene within healthcare and sportswear applications.