Evaluation of Photonic Materials with Biomimetic Structural Coloration

Importance of the Topic

Structural coloration inspired by natural examples such as morpho butterflies, peacocks and jewel beetles offers vibrant, non-fading hues without the need for traditional pigments. Biomimetic photonic materials harness microscopic architectures to control light interference and scattering, promising sustainable, tunable colorants for applications in inks, coatings and optical devices.

Aims and Study Overview

This study evaluated synthetic melanin-mimicking particles composed of polystyrene cores coated with polydopamine (PSt@PDA). By varying core diameter and coating thickness, researchers sought to reproduce iridescent and non-iridescent structural colors and to quantify their spectral and angular optical responses.

Methodology and Instrumentation

The PSt@PDA samples were characterized using a SolidSpec-3700DUV spectrophotometer equipped with a variable-angle absolute reflectance attachment. Measurements spanned 380–780 nm at incident angles of 5°, 12°, 30° and 45°, with a 1 mm beam aperture and 5 nm slit width. Color coordinates (CIE x,y) were calculated using commercial software. Particle arrangement was observed by combining laser scanning and probe microscopy on an SFT-4500 Nano Search Microscope, capturing 5 µm × 5 µm height images to resolve colloidal ordering.

Main Results and Discussion

Increasing polydopamine thickness produced a systematic redshift in reflectance peaks, shifting visual appearance from blue to green to yellow. Larger core diameters likewise induced redshifts. Angle-dependent measurements on thinly coated (iridescent) samples exhibited a blueshift as incident angle increased, consistent with Bragg reflection behavior. Microscopy revealed that thin PDA coatings formed well-ordered colloidal crystals, while thick coatings led to disordered, amorphous arrangements, explaining the loss of angular color dependence in non-iridescent samples.

Benefits and Practical Applications

Tunable structural coloration through precise control of particle size, refractive index and assembly offers a pathway to durable, environmentally friendly colorants. Potential uses include anti-counterfeiting inks, colorimetric sensors and decorative coatings requiring stable, non-toxic pigments.

Future Trends and Applications

Advances may focus on dynamic color-changing systems responsive to external stimuli (e.g., pH, temperature), integration into flexible displays, and scale-up of biomimetic assembly processes. Combining structural color with functional materials may yield smart coatings for sensing and energy applications.

Conclusion

This work demonstrates that melanin-mimicking PSt@PDA particles can be engineered to produce vivid iridescent and non-iridescent colors. Spectral and microscopic analyses confirm that color tuning arises from controlled core size, coating thickness and particle ordering, pointing toward versatile, sustainable photonic materials.

Reference

1. Shimadzu Corporation. New World Opened Up by Biomimetics.
2. Yoshioka S. & Kinoshita S. Effect of Macroscopic Structure in Iridescent Color of the Peacock Feathers. Forma. 17:169 (2002).
3. Kawamura A., Kohri M., Morimoto G., Nannichi Y., Taniguchi T. & Kishikawa K. Full-Color Biomimetic Photonic Materials with Iridescent and Non-Iridescent Structural Colors. Scientific Reports. 6:33984 (2016).