Oct 22, 2025

Eco-friendly polymer particles shimmer like opals and never fade

Researchers created polymer particles that mimic opal's lasting colors, offering a sustainable way to make vivid pigments for inks, coatings, and displays.

(Nanowerk News) A research team at UNIST has found a way to recreate the dazzling colors of opal gemstones—using plastic, not minerals. The group developed a new method for making polymer-based particles that shimmer with vivid, stable color, offering a sustainable alternative to conventional dyes and pigments (Angewandte Chemie International Edition, "Disordered Inverse Photonic Beads Assembled From Linear Block Copolymers").

Opals owe their shifting rainbow hues to their internal structure: tiny silica spheres stacked in a precise pattern that bends light. Inspired by this, Professor Kang Hee Ku and her team in UNIST’s School of Energy and Chemical Engineering designed synthetic “inverse photonic glass” particles using amphiphilic block copolymers. These materials, made from poly(styrene-block-4-vinylpyridine) or PS-b-P4VP, self-assemble into porous, nanostructured beads that produce brilliant, angle-independent colors—no fading, no chemical dyes required.

The breakthrough comes from a scalable emulsion-templating process. In this method, water seeps into an organic solution, creating nanoscale pockets that solidify into pores as the solvent evaporates. The resulting microparticles, each only tens of micrometers wide, contain tiny cavities hundreds of times smaller that control how light interacts with the material.

This process uses the physics of surface tension and the chemistry of self-assembling polymers. The outer shell, made of hydrophobic polystyrene, resists water, while the inner structure forms naturally from the molecular arrangement of the copolymer blocks. By adjusting the chemical composition, researchers can precisely control pore size, shell thickness, and color—spanning the full visible spectrum.

Unlike natural opal, which changes color when viewed from different angles, these synthetic pigments maintain a steady hue no matter how they’re seen. The team demonstrated fine color control by tweaking surfactants, molecular weights, and chemical modifications of the polymers. They even embedded the particles into hydrogels to make “optical inks” that can print colorful, detailed patterns using standard printing tools.

“By employing relatively simple linear block copolymer structures, we have developed a versatile platform for generating vibrant, angle-independent structural colors,” said Professor Ku. “This technology holds promise for applications in displays, security features, and functional coatings.”

Source: UNIST (Note: Content may be edited for style and length)