Abstract
The fabrication of self-assembled cellulose nanocrystal (CNC) films of tunable photonic and mechanical properties using a facile, green approach is demonstrated. The combination of tunable flexibility and iridescence can dramatically expand CNC coating and film barrier capabilities for paints and coating applications, sustainable consumer packaging products, as well as effective templates for photonic and optoelectronic materials and structures.
Highlights
Cellulose is an abundant and sustainable biopolymer that has gained renewed interest in materials science.[1]
cellulose nanocrystals (CNCs) can be obtained by controlled acid hydrolysis of cellulosic biomass, yielding spindle-shaped nanocrystals on the order of 5–20 nm in diameter and a few hundred nanometers in length.[11,12]
Hydrolysis using sulfuric acid generates sulfate ester groups on the CNC surface that are crucial for the stabilization of aqueous colloidal suspensions of CNCs.[10b,11,12] Significantly, sulfate-functionalized CNCs organize into a chiral nematic lyotropic liquid crystalline (LLC) phase,[11] and upon slow evaporation of water, the organization of CNCs present in the LLC phase can be retained in solid films endowing the resulting materials with a helicoidal structure and brilliant iridescent colors.[14]
Summary
Cellulose is an abundant and sustainable biopolymer that has gained renewed interest in materials science.[1]. We propose a novel, facile and scalable approach based on the co-assembly of zwitterionic (Zw) surfactants with CNCs resulting, upon evaporation, in flexible, iridescent films with tunable and controllable chiral nematic order. The amount of Zw surfactant (DMAPS) was determined by gravimetry on the final dry films and confirmed by elemental analysis of the nitrogen and sulfur contents, Table 1.
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