Solvent-dependent morphology and anisotropic microscopic dynamics of cellulose nanocrystals under electric fields.

Cellulose nanocrystals (CNCs) are interesting for the construction of biomaterials for energy delivery and packaging purposes. The corresponding processing of CNCs can be optimized through the variation of intercellulose interactions by employing different types of solvents, and thereby varying the degree of cellulose hydrogen bonding. The aim of this work is (i) to show how different types of solvents affect the self-assembled morphology of CNCs, (ii) to study the microscopic dynamics and averaged orientations on the CNCs in aqueous suspensions, including the effect of externally imposed electric fields, and (iii) to explore the nonlinear optical response of CNCs. The homogeneity of self-assembled chiral-nematic phase depends on both the polarity of the solvent and the CNC concentration. The variation of the chiral-nematic pitch length with concentration, as determined from real-space and Fourier images, is found to be strongly solvent dependent. The anisotropic microdynamics of CNCs suspension exhibits two modes, related to diffusion parallel and perpendicular to the (chiral-) nematic director. We have found also the coupling between translational and orientational motion, due to existing correlation length of twisted nematic elasticity. Preliminary second-harmonic generation experiments are performed, which reveal that relatively high field strengths are required to reorient chiral-nematic domains of CNCs.