Direct Laser Writing of Composite Materials towards Bio-Inspired Photonic Actuators

Colour and colour changes play hugely important roles in the natural world, enabling organisms to camouflage, signal, and mimic. These responsive colour changes are a result of a phenomenon known as structural colour. The reflection of colour in these materials is dependent on a high refractive index and ordered structures with feature sizes comparable with wavelengths in the visible range. [1] In nature, this is often achieved through exploitation of naturally occurring crystals of chitin and guanine that can be ordered from the nano to millimetre scales.[2]<br/><br/>Synthetic analogues of structural colour have often been achieved through the use of liquid crystals, colloidal nanoparticles, and sol gel chemistry, resulting in colloidal crystal assemblies and photonic films.[3] Extrinsic structural colour has also been approached through the use of additive and subtractive manufacturing techniques such as etching, e-beam lithography, and nanoimprint lithography, often from dielectric material. [4] The combination of nanocomposite materials and Direct Laser Writing (DLW) using two-photon polymerisation (2PP) has emerged as a route to obtain ordering of a material in both an extrinsic and intrinsic manner mimicking that seen in biology.[5,6]<br/><br/>In this work we present DLW as a method to produce materials with controlled structural properties on the nm and micron scale in a precise manner resulting in a wide gamut of responsive colours through the exploitation of stimuli-responsive nanocomposite materials, to create responsive photonic materials inspired by those in the natural world. This presentation will encompass a range of nanocomposite materials including colloidal particles, liquid crystalline cellulose, polypeptides, and guanine nanocrystals. Upon incorporation into stimuli responsive materials, we present arrays of printed microstructure pixels, exhibiting dynamic structural colour to stimuli such as light, temperature, humidity and concentration. These materials offer a range of applications in technology such as active display technologies, steganography, and polarisation encryption.<br/><br/>[1] Parker, A.R., (2000). ‘515 million years of structural colour’, Journal of Optics A: Pure and Applied Optics, 2(6), R15.<br/>[2] Gur, D., Leshem, B., Pierantoni, M., Farstey, V., Oron, D., Weiner, S. and Addadi, L., (2015), ‘Structural basis for the brilliant colors of the sapphirinid copepods’, Journal of the American Chemical Society, 137(26), 8408-8411.<br/>[3] Fenzl, C, Hirsch, T., and Wolfbeis, O. (2014), "Photonic crystals for chemical sensing and biosensing." Angewandte Chemie International Edition 53(13), 3318-3335.<br/>[4] Zhu, L., et al. (2015) "Flexible photonic metastructures for tunable coloration." Optica 2(3) 255-258.<br/>[5] Delaney, C., Qian, J., Zhang, X., Potyrailo, R., Bradley, A.L, Florea, L., (2021). ‘Direct laser writing of vapour-responsive photonic arrays’, Journal of Materials Chemistry C 9, 11674.<br/>[6] Qian, J., et al. (2023) "Responsive spiral photonic structures for visible vapor sensing, pattern transformation and encryption." Advanced Functional Materials 2211735.