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

Kyongok Kang,Alexey Eremin

doi:10.1103/physreve.103.032606

Abstract

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.

Highlights

Cellulose nanocrystals (CNCs) received much scientific attention due to their versatile applications, especially in the fields concerning biodegradable and biointegrated materials, employed to bioenergy and soft electronics
The vertically aligned small-angle electric-field dynamic light scattering instrument (SAeDLS) setup, equipped with a He-Ne laser, probes small scattering angles q in the range q ∼ 1.8–4.8 μm−1, so that the intensity-correlation functions resolve the dynamics on length scales 2π /q ∼ 1.3–3.5 μm, which is in the range of correlated length scales of CNC particles
There is on average a preferred orientation of the chiral-nematic pitch in the Fourier image, such that the spatial extent of correlated CNC rods exist in the real-space morphology

Summary

Introduction

Cellulose nanocrystals (CNCs) received much scientific attention due to their versatile applications, especially in the fields concerning biodegradable and biointegrated materials, employed to bioenergy and soft electronics. The broad range of their chemical modification is connected to the variation of hydrogen-bond-induced intercellulose interactions, as well the interaction between cellulose with other types of biomolecules, for example, DNA, polysaccharides, and chitin. A further application of cellulose is the scaffolding of tissue for regenerative biomedical substitutes [3]. It is, not yet clear how to tune the morphological structure of CNCbased biomaterials, and how to control the binding properties to external agents. Not yet clear how to tune the morphological structure of CNCbased biomaterials, and how to control the binding properties to external agents This requires a better understanding of the inter-CNC interactions and the resulting self-assembly

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