The current work investigates how the nanoscale conformal coating layers of non-chiral polymeric materials can influence the chiral nematic liquid crystal (CLC) behaviors of the rodlike cellulose nanocrystals (CNCs), the bio-derived nanomaterials that have attracted significant attention. For this, we developed strategies to coat the CNC rods on the single-particle level with a homogeneous bioinspired polydopamine (PDA) layer, leading to well-defined core−shell CNC@PDA rods with various PDA coating thicknesses and excellent colloidal stability. Comprehensive investigation revealed that the CNC@ PDA hybrid nanorods in concentrated suspensions form well-defined nematic liquid crystal phases with clear phase separation behavior that depend on the rod concentrations and ionic strengths, typical of charged rods. Most intriguingly, the nematic LC phases formed by the CNC@PDA rods with the PDA coating thickness achieved herein are indeed the perfect CLC phases, which form following the classic pathway of nucleation and coalesce of chiral tactoids and have colorful chiral fingerprints standing out from the dark suspensions. The pitches of the CLC phase increase sharply with increasing PDA coating thicknesses and are significantly larger than those of the pristine CNCs. Such observations can be attributed to the blurring effects of the PDA coating on the intrinsic surface chiral features of CNC of whatever origins that drive the formation of the CLC phases, resulting in weakening chiral interactions between CNC@PDA rods. Besides benefiting the understanding of the long-sought origin of the CLC phases of the pristine CNC, the current work demonstrates the possibility of controlling the CLC phase behaviors of CNC by tuning the thickness of the coating materials and also serves as the first example of directly transferring the unique chirality of CNC to other non-chiral materials.
Many biological species combine the helical organization of cellulose or chitin microfibrils with broadband light absorption of black melanin to produce brilliant structural colors with metallic and glossy effects and other diverse functions. In this work, based on core−shell CNC@PDA chiral nanorods consisting of cellulose nanocrystals (CNCs) as the core and melanin-like polydopamine (PDA) as the shell that can form welldefined chiral liquid crystal phases, we report chiral photonic materials that closely mimic the unique coloration mechanisms and functionalities mastered by several biological species. The photonic films formed by such single CNC@PDA nanorods have brilliant iridescent structural colors originating from selective reflection of circularly polarized lights by the helical organization of CNC@PDAs across the films. Furthermore, the colors of such films have background-independent brightness, high visibility, and metallic effects that arise from the light absorption of the PDA component. Especially, the color ranges and metallic effects of the films can be conveniently tuned by varying the thickness of the PDA shell. In addition, the UV absorption and hygroscopic properties of PDA endow these CNC@PDA films with efficient broadband UV shielding and sensitive humidity-induced dynamic color changes. Due to the mussel-like superior adhesion of PDA, CNC@PDAbased photonic coatings can be formed conformably onto diverse kinds of substrates. A shiny eye shadow with viewing angledependent colorful patterns was used to demonstrate the potential applications. With combinations of multiple unique properties in one photonic material fabricated from a single building block, these CNC@PDA-based films are expected to have potential applications in cosmetics, UV protection, anticounterfeiting, chiral reflectors, etc.
Anisotropic hydrogel fibers consisting of distinct blocks with heterogeneous internal structures and chemical components are expected to have many advanced functionalities. Based on the chiral liquid crystals (CLCs) of the...
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