Structural color formation in soft colloidal systems represents a promising approach toward stimuli-responsive photonic materials. In this study, we investigated the assembly of poly(N-isopropylacrylamide) (PNIPAm)-based microgels incorporating varying percentages of anionic (methacrylic acid), neutral (acrylamide), and cationic (2-(dimethylamino)ethyl methacrylate) comonomers to create multifunctional colloidal building blocks capable of forming dynamic structural colors. Through synthesis optimization and surfactant-mediated size control, we obtained libraries of copolymer microgels with precisely tailored particle diameter, surface charge, and stimuli-responsive swelling behavior.

We generated structural colors across the visible spectrum by colloidal crystal assembly through thermal annealing and modulated the interparticle spacing and consequently the reflected wavelengths by changing the microgel concentration. Additionally, by fine-tuning the microgel responsiveness, we engineered materials with precise wavelength shifts in the reflected color upon environmental stimuli (temperature or pH).

Our findings provide key insights into the interplay between microgel responsiveness, compressibility, and the resulting structural color formation that are expected to support advanced multifunctional colloidal sensors, coatings, and optical tags.

Figure 1: Schematic representation of structural color formation through thermally induced assembly of copolymer microgels. The reflected wavelengths are dependent on the microgel size and concentration.

[1] M. Kraus, M. Malekovic, I.A. Dinu, C.G. Palivan, Small Science, 2026, 6

[2] M. Hildebrandt, D.P. Thuy, J. Kippenberger, T.L. Wigger, J.E. Houston, A. Scotti, M. Karg, Soft Matter, 2023, 19

[3] Y. Xia, S. Gao, H. He, X. Wang, Z. Zeng, B. Chen, N. Zhou, M. Cao, S. Wang, Journal of Physical Chemistry, 2020, 124