Song Jianing, Parker Richard M, Frka-Petesic Bruno, Deng Tao, Xu Luqing, Deng Xu, Vignolini Silvia, Shen Qingchen
Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK.
Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Shenzhen, 518110, P. R. China.
Adv Mater. 2025 Jun;37(22):e2416607. doi: 10.1002/adma.202416607. Epub 2025 Jan 29.
Photonic pigments, especially those based on naturally-derived building blocks like cellulose nanocrystals (CNCs), are emerging as a promising sustainable alternative to absorption-based colorants. However, the proposed manufacturing methods for CNC pigments, via either grinding films or emulsion-based production, usually require several processing steps. This limits their commercialization by increasing the costs, timescales, and environmental impacts of production. Toward addressing these challenges, it is reported that photonic pigments can be produced in a single process by drying microdroplets of aqueous CNC suspension on a superhydrophobic surface. Such liquid-repellent substrate ensures the microdroplets maintain a near-spherical shape, enabling the radial self-organization of the cholesteric phase. Upon drying under ambient conditions, the CNC mesophase becomes kinetically arrested, after which the strong capillary forces induced by water evaporation result in extensive buckling of the microparticle. This buckling, coupled with prior tuning of the CNC formulation, enables photonic pigments with adjustable color across the visible spectrum. Importantly, the elimination of an emulsifying oil phase to create microdroplets enables a much faster drying time (≈40 min) and improved color stability (e.g., polar solvents, elevated temperatures), while the reduction in reagents (e.g., oils, surfactants) and post-processing steps (e.g., solvent, heat) improves the sustainability of the fabrication process.
光子色素，尤其是那些基于纤维素纳米晶体（CNC）等天然构建基块的色素，正成为一种有前途的可持续替代吸收型着色剂的材料。然而，目前提出的用于制造CNC色素的方法，无论是通过研磨薄膜还是基于乳液的生产，通常都需要几个加工步骤。这通过增加生产成本、生产时间和环境影响限制了它们的商业化。为了应对这些挑战，有报道称光子色素可以通过在超疏水表面上干燥水性CNC悬浮液的微滴在单一过程中生产。这种拒液性基材确保微滴保持近乎球形，从而使胆甾相能够进行径向自组织。在环境条件下干燥后，CNC中间相在动力学上被捕获，此后水蒸发引起的强大毛细作用力导致微粒发生广泛屈曲。这种屈曲，再加上之前对CNC配方的调整，使得能够制备出在可见光谱范围内颜色可调的光子色素。重要的是，消除用于形成微滴的乳化油相能够实现更快的干燥时间（约40分钟）并提高颜色稳定性（例如，极性溶剂、高温），同时减少试剂（例如，油、表面活性剂）和后处理步骤（例如，溶剂、加热）提高了制造过程的可持续性。
