Responsive Photonic Filaments from Confined Self-Assembly of Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) hold transformative potential for sustainable photonics, particularly in applications such as polarization-selective devices and chiroptical sensors. However, conventional CNC derivatives are primarily limited to dense flat films, restricting their functionalization in soft fibers and wearable textiles. Advancing CNCs into infinitely extending cylindrical filaments presents an opportunity to unlock fascinating applications, yet this transformation is often hindered by the Plateau-Rayleigh instability, leading to the breakup of CNC suspensions into droplets. Here, we propose an innovation strategy for the continuous and scalable production of chiral photonic filaments by confining the photo-cross-linking of CNC/poly(ethylene glycol) diacrylate precursors within cylindrical microtubules. The resulting filaments, driven by both shear flow and chiral self-assembly, exhibit a high degree of orientation along their central axis while preserving the nanohierarchical structure of the uniaxial nematic phase. Notably, these filaments achieve an orientation order parameter of 0.91, coupled with exceptional mechanical performances (14 MJ·m^-3), as well as dynamic interference color-change capabilities in response to variations in hygroscopicity or applied mechanical strain. We present a proof-of-concept for optical fabrics using these photonic filaments, which supports the development of smart textiles and fashionable clothing, thereby significantly enriching the diversity and design possibilities of CNC-based materials.