Chiral-structural-color materials produce color through microscopic structures that interact with light rather than through pigmentation or dyes. Some beetle exoskeletons, avian feathers, butterfly wings, and marine organisms feature these structures naturally, producing iridescent or polarization-dependent colors. Over the last 10-15 years, scientists have made progress in developing artificial chiral-structural-color materials.
Recently, Chinese researchers have made a breakthrough in the field by discovering that microdomes made from common polymers exhibit tunable chiral structural colors with broad-spectrum capabilities and multiple polarization-modulated chirality. This advancement could have significant implications for applications in displays, sensors, and data security.
Published in PNAS on February 25, the study was led by Prof. LI Mingzhu's team from the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences. The researchers discovered that microdomes composed of widely available polymers exhibit polarization-modulated chiroptical responses, with an exceptional dissymmetry factor of approximately ~1.998-setting a new record for chiral materials. Such a high level of dissymmetry means that the material exhibits almost total polarization selectivity between left- and right-handed circularly polarized light.
Artificial chiral-structural-color materials, which exhibit vivid colors due to their intricate nanostructured chirality, offer the advantage of high-dimensional controllable channels, including wavelength, amplitude, polarization, and phase, making them highly versatile and functional.
In this study, through experimental and theoretical investigations, the researchers revealed that the chiroptical response results from a phase delay between two orthogonal linearly polarized components of incident light. The light undergoes multiple total internal reflections (TIRs) within the microdomes, contributing to the material's unique optical properties. These microdomes are not only tunable across a broad range of wavelengths but also allow for switching through modulation of the incident polarization.
Furthermore, the researchers identified that the brightness of the structural color in the microdomes follows a cosine-squared function in relation to the polarization angle, mirroring Malus' law. This relationship opens up new possibilities for information encoding, offering a degree of freedom that extends beyond the traditional two-dimensional (2D) hexagonal symmetry plane.
In addition, the integration of chiral-structural-color microdomes into contact lenses opens up avenues for advancing information security in identity authentication and potentially enhancing human-computer interaction through the incorporation of diverse optical components.
This work was supported by the National Science Fund of China for Distinguished Young Scholars, the National Natural Science Foundation of China, and the National Key R&D Program of China, among others.
Optical properties of the chiral structural color microdomes and a concentric-arc pattern using these microdomes on a contact lens for identity authentication mimicking the personal identification system based on iris patterns. (Image by LI's group)
