Dynamic Viscoelastic Functions of Liquid-Crystalline Chitin Nanofibril Dispersions

The dynamic viscoelastic functions of aqueous chitin nanofibril (ChNF) dispersions are defined by their liquid-crystalline fibril arrangement. Four ChNF dispersions with different structures were prepared from squid-pen β-chitin, by sonication in aqueous acetic acid at pH 3 for 4-40 min. Squid-pen β-chitin was disintegrated into randomly oriented bundles of ChNFs during the initial stage of sonication and then became more finely dispersed with further sonication up to 8 min. The additional sonication resulted in the individualization of the approximately 3 nm-wide ChNFs. The individual ChNFs self-organized into a nematic liquid crystalline phase. All ChNF dispersions showed power-law concentration c dependences of their storage moduli G' at a certain angular frequency ω (G_ω' = Ac^α). The front factor A was positively correlated with the degree of disintegration. The exponent α increased from 2.7 to 3.8-3.9, as the ChNF dispersion self-organized from the randomly dispersed structure into the nematic-ordered fibril arrangement. This demonstrated an enhancement in the solid concentration dependence.