From Brittle to Flexible: Influence of Glucose‐Based Additives on Cellulose Nanocrystal Self‐Assembly in Suspension and Dried Photonic Films

Abstract Cellulose nanocrystal (CNC) films can exhibit reflective and iridescent coloration due to their self‐assembled structure, but are brittle. This study compares glucose (monosaccharide), maltose (disaccharide), and gluconic acid (acidic sugar) as plasticizers and links suspension self‐assembly behavior to the optical and mechanical properties of the resulting films. Glucose‐plasticized films have been previously studied, but maltose and gluconic acid have not yet been applied in this capacity. Here, glucose and maltose do not change CNC liquid crystalline suspension properties, whereas gluconic acid significantly increases the critical concentration for liquid crystal formation and the chiral nematic pitch. All additives redshift the film color, with gluconic acid inducing the largest redshift; the homogeneity of the optical response trends as follows: pure CNC > gluconic acid > glucose > maltose. The pronounced changes induced by gluconic acid are attributed to its acidity and negatively charged nature, which modify CNC‐CNC interactions. Added sugars increase strain‐at‐break and decrease Young's modulus – for example, an eight‐fold increase in strain‐at‐break and a nine‐fold decrease in Young's modulus are observed with gluconic acid. These results indicate that plasticizer identity offers a straightforward lever to tune CNC film properties for photonic applications but requires balancing mechanical performance against optical quality.