Fabrication of Responsive 4D Micro-Structures for Dynamic Structural Color and Optical Sensing

Self-assembly of colloidal particles into crystalline colloidal arrays have attracted great interest from chemists, physicists and materials scientists alike due to their broad applications in the fields of optics and photonics¹. In particular, application of colloidal crystal arrays offers a means for controlling and manipulating light flow, and gives rise to some of the most brilliant structural colors. This phenomenon is also present in nature, where many species of birds, insects, butterflies, fish and even flowers, owe their vivid color to hierarchical assemblies of photonic structures.<br/><br/>Changing the structural color of photonic crystalline structures typically requires the synthesis of different size particles, in order to modulate inter-particle distance². This can add different degrees of difficulty as precise control of particle size and inter-particle distance in the self-assembly process can be time-consuming. In this work, we prove how using just one size polymer particle spheres, a wide gamut of reflected colours can be obtained in a range of different polymer matrices.<br/><br/>Using direct laser writing (DLW) in nanocomposite photoresists (at particle concentrations conducive to self-assembly), we can fabricate complex 3D microstructures with sub-micron feature sizes. Furthermore the DLW fabrication technique allows for fine control over a series of fabrication parameters, such as laser power, structure slicing and hatching, thereby providing minute control over the inter-particle distance in all 3 dimensions, to obtain hierarchically ordered nanocomposite microstructures showing a wide gamut of color.<br/><br/>We present the expansion of this work to encompass soft, stimuli-responsive polymers in which an external stimulus can be further used to vary periodicity of the ordered nanocomposite, thereby further changing the reflected colour in and out of the visible spectrum. We will show routes of exploitation for this approach which span sensing and encryption.<br/><br/>In conclusion, the strategy presented herein offers a novel and efficient route for creating responsive photonic microstructures that can be used qualitatively (for analyte determination) or qualitatively (for go/no go interventions).<br/><br/>1. Zhang, H., Bu, X., Yip, S., Liang, X., & Ho, J. C. (2020). Self Assembly of Colloidal Particles for Fabrication of Structural Color Materials toward Advanced Intelligent Systems. Advanced Intelligent Systems, 2(1), 1900085.<br/>2. Li, R., Zhang, S., & Zhang, R. (2023). Recent progress in artificial structural colors and their applications in fibers and textiles. Chemistry Methods, e202200081.