Research and Application Progress of CNC Structural Color Materials
Structural Color Originates from Ordered Structures, Not Conventional Dyes
Cellulose nanocrystals (CNCs) are rod-like nanoparticles with a defined aspect ratio and surface charge. Under appropriate concentrations and dispersion conditions, CNCs can form an ordered cholesteric liquid-crystalline structure in an aqueous phase. As water evaporates, this helical arrangement can be preserved within the resulting solid film. When the helical pitch falls within an appropriate range relative to the wavelength of visible light, the material selectively reflects specific wavelengths, giving rise to structural colors such as blue, green, and red.
Therefore, the key to structurally colored CNCs is not that the CNC particles themselves possess color, but rather that CNCs self-assemble into a periodic photonic structure. Factors such as CNC concentration, ionic strength, surface charge, particle size, evaporation rate, substrate, additives, and drying-induced stress can all influence the final helical pitch and, consequently, the macroscopic color of the material.
Research Focus Shifts from Color Generation to Controlled Self-Assembly
In recent years, research has shifted from investigating whether CNCs can generate structural color to understanding how to achieve stable and controllable color regulation. On one hand, the helical pitch can be tuned by controlling ionic species, polymers, small molecules, plasticizers, and interfacial interactions. On the other hand, macroscopic orientation and color uniformity can be improved through shear alignment, confinement, templating, external fields, and hierarchical layered structures.
Another critical challenge lies in shrinkage and kinetic arrest during the drying process. As water evaporates, CNC suspensions undergo a sequence of concentration, liquid-crystalline phase formation, structural fixation, and solid-state shrinkage. The kinetics at each stage can influence the final optical response. Therefore, the development of structural-color CNC materials requires simultaneous control of both the raw-material parameters and the film-forming process.
2026 Research Trends: From Optical Materials to Multifunctional Devices
Recent reviews indicate that CNC-based self-assembled structural colors are increasingly being integrated with conductive materials, electrochromic systems, photothermal components, and advanced manufacturing technologies. Research is expanding into areas such as visual sensing, flexible electronics, smart photonic textiles, passive daytime radiative cooling, photothermal anti-icing, and energy conversion.
This evolution suggests that the value of CNC structural colors is moving beyond “dye-free coloration” toward a multifunctional materials platform that integrates structure, optical properties, and responsive functionality. For example, structural changes induced by humidity, mechanical strain, solvents, or temperature can be translated into color variations that serve as visually readable signals. By incorporating functional polymers, the inherent brittleness of pure CNC films can be reduced while simultaneously introducing flexibility and stimuli-responsive capabilities.
Three Key Challenges Remain for Practical Applications
The transition toward practical applications still requires addressing three key challenges.
First, environmental stability. Changes in humidity can affect the cellulose network and helical pitch, resulting in color shifts. Second, large-area uniformity. Although evaporation in small laboratory-scale vessels is relatively easy to control, continuous coating and large-area drying can introduce flow fields, edge effects, and drying gradients. Third, mechanical performance. Pure CNC structural-color films are typically brittle and require strategies such as plasticization, polymer blending, or layered architectures to improve their flexibility and mechanical robustness.
Therefore, structural-color CNC materials intended for industrialization must simultaneously address self-assembly capability, batch-to-batch consistency, ionic environment, film-forming process window, and post-treatment stability.
Application Areas of Interest for CelluBio
Structural-color-grade CNCs are well suited for early-stage development in areas such as photonic films, self-assembly research, structural-color coatings, sensing, and anti-counterfeiting applications. In practical development, it is recommended to first establish a stable film-forming process window using a baseline CNC system, and then gradually introduce PEG, PVA, or other functional components. This stepwise approach helps minimize interference with CNC self-assembly caused by the simultaneous introduction of multiple variables.
Sources and Further Reading
• Self-assembled cellulose nanocrystal: Expanding structural color materials into next-generation functional applications: A review. International Journal of Biological Macromolecules, 2026.
• Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications. Chemical Reviews, 2023.
• Advances in structural color composite films based on cellulose nanocrystals. Industrial Crops and Products, 2024.
Note: This article is intended for technical exchange and discussion within the industry and is based on publicly available research and technological developments. The specific properties and performance of the materials may vary depending on raw materials, surface chemistry, dispersion state, formulation, and processing conditions. Actual applications should be validated through laboratory-scale testing. For applications involving food, medical, or other regulated fields, applicable regulations and compliance requirements for the end products must also be satisfied.