All bio-based chiral nematic cellulose nanocrystals films under supramolecular tuning by chitosan/deacetylated chitin nanofibers for reversible multi-response and sensor application

Abstract

Application of green and renewable all bio-based resources on functional nanomaterials has been of much interest, but often limited by their complex supramolecular construction. Herein, two kinds of most abundant biopolymers on earth, cellulose and chitin were selected as raw materials to prepare all bio-based iridescent films. Cellulose nanocrystals (CNCs) were cooperated with chitosan (CS) or deacetylated chitin nanofibers (DChN) at various content ratios to fabricate chiral nematic films via evaporation-induced self-assembly (EISA). The iridescent films showed increased crystallinity (80%∼ 90%) than pristine CNCs as well as lowered crystallite sizes, due to hydrogen bonding linkages and hydrophobic interactions between CNCs and amphiphilic CS/DChN with diverse degrees of acetylation. Obviously enlarged helical pitches were achieved by intercalation of CS/DChN, which reflected optical light with red-shifted wavelength bands. CS and DChN also improved the hydrophobicity of the nanocomposite films with various degrees, but both maintaining good biocompatibility proved by cell viability assay. The films showed wide-range/fast humidity and pH stimuli response capabilities via visible colorimetric changes. Moreover, the materials were equipped with satisfying reversible response, which was confirmed by repeated water ink writing-drying and acidic/alkaline vapor evaporation tests for 10 cycles. A food freshness sensor device was assembled on quick response (QR) code for sensitive and convenient recognition by smart phone, exhibiting high potential on multi-functional sensors of the all bio-based sustainable materials.