Paper-based sacrificial template method: Preparation of large-area, robust, and reusability iridescent photonic crystal film

The vibrant colors in our daily lives predominantly come from chemical dyes and pigments. However, these traditional colorants face challenges such as fading and environmental pollution. Inspired by natural structures like butterfly wings and peacock feathers, scientists have begun exploring an alternative coloring mechanism—structural color. Generated through the interaction between microscopic structures and light, structural color produces vivid color and iridescent effects unattainable with conventional dyes. Among the structures capable of producing such colors, photonic crystals (PC) -- artificial microstructures composed of periodically arranged materials with different refractive indices -- are one of the most commonly used. Embedding an orderly array of microspheres into a polymer matrix to form large-area, flexible, free-standing photonic crystal films not only eliminates the need for rigid substrates but also enhances mechanical stability. These advantages make such PC films promising for applications in displays, optical devices, anti-counterfeiting, wearable electronics, sensors, and adaptive camouflage.

However, current technologies for PC film are constrained by the limited refractive index contrast between the microspheres and the polymer matrix. Potential solutions often rely on harsh processing conditions—such as high-temperature calcination or hydrofluoric acid etching—to construct specific architectures like hollow silica spheres or inverse opals, or require large-scale roll-to-roll equipment. Consequently, developing a simple strategy to produce PC-polymer composite films that simultaneously exhibit bright color, good flexibility, excellent mechanical durability, and reusability remains a critical challenge.

To address this, Professor Suli Wu’s team at Dalian University of Technology has proposed an ingenious strategy to fabricate large-area, free-standing PC films that combine vibrant iridescence, outstanding mechanical strength, and remarkable durability. The core innovation of this research lies in the use of cheap porous paper as a "sacrificial template." The high-performance PC composite film is constructed through four key steps: (1) evaporation-induced self-assembly of a mixture of monodisperse PMMA microspheres and binders on paper to form a crack-free, brightly colored photonic crystal layer; (2) application of a transparent aqueous acrylic resin onto the photonic crystal layer, followed by curing to form a top protective layer; (3) peeling off the paper substrate and encapsulating the exposed bottom of the photonic crystal layer with the same aqueous acrylic resin, followed by curing, ultimately forming a unique "polymer-PC-polymer" sandwich-structured composite film.

This unique sandwich design produces a synergistic "1+1>2" effect, delivering bright iridescent colors (tunable across the spectrum from purple to red), excellent structural stability (withstanding 100 dry/wet rubbing tests), and notable flexibility and reusability (capable of recovering completely after extreme stretching, crumpling, or folding via brief heat treatment). Furthermore, by replacing the bottom polymer layer with a double-sided adhesive, a universally adherent photonic crystal sticker can be created. It firmly adheres to various surfaces such as wood, plastic, glass, and even curved fingernails, demonstrating broad application prospects.

The team published their review in Nano Research on December 5, 2025.

Other contributors include Yaqun Han, Jingyuan Huyan, Jiaming Huyan, Hao Zong, and Shufen Zhang from the State Key Laboratory of Fine Chemicals, Frontier Science Center for Smart Materials, School of Chemical Engineering, Dalian University of Technology, Dalian 116024.

This work was supported by the National Natural Science Foundation of China (22178047 and 21878042), the Fundamental Research Funds for the Central Universities (DUT22LAB610), and Liaoning province science and technology plan projects (2022JH2/101300233). The authors acknowledge the assistance of DUT Instrumental Analysis Center.

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.