Tuning Chiral Nematic Pitch of Bioresourced Photonic Films via Coupling Organic Acid Hydrolysis

Controlling the iridescent photonic film generated by self-assembly of colorless cellulose nanocrystal (CNC) from the nanoscale to macroscale is challenging. This study combines experimental and computational approaches to systematically investigate the correlation between electrostatic interactions and chiral nematic structures. The chiral nematic order of the CNC colloidal is preserved in solid films after the evaporation of water. The cross-sections of the iridescent film show a clear left-handed helical arrangement of nanocrystals. The helical structure with the aid of acrylic acid exhibits longer organized patterns. This work reveals that compared to CNC prepared by pure sulfuric acid (zeta potential -37.1 mV), the CNC prepared using coupled mineral sulfuric and organic acrylic acid has a higher zeta potential (-67.2 mV), which induces the increase of helical pitch of the cholesteric nematic phase from 312 to 409 nm and a red shift of the iridescent film. Consequently, the tuning of reflected light wavelength lies in the variation of chiral nematic pitch inside the layered structure, which gives rise to different iridescent colors. The bioresourced photonic film is appealing to both academia and industry where optical and photonic components are essential.