Abstract
Motivated by the development of cellulose-based functional materials, we investigate the microscopic dynamics of suspensions of cellulose nanocrystals (CNCs) at different ionic strengths, both in the absence and in the presence of AC electric fields and for various temperatures. A concentration of 5 wt% of the CNCs is chosen for which the dispersions are in the full chiral-nematic state at low ionic strengths. Dynamic light scattering is used to characterize the wave vector-dependent decay rates of number-density fluctuations. Contrary to an isotropic suspension, the dispersion relations (the wave vector dependence of the correlation-function decay rates) as obtained by means of depolarized light scattering are found to exhibit anomalous behavior. The dispersion relations, both without and with an external field, exhibit minima at small wave vectors, which is attributed to coupling of translational motion to the orientation of the CNCs, shown in the chiral-nematic state. The location of the minima is found to weakly depend on ionic strength and shifts significantly towards larger wave vectors upon applying an external electric field for sufficiently high ionic strengths. Finally, preliminary results are presented for smaller length-scale density fluctuations (at larger wave vectors) as a function of temperature, revealing the anisotropic mobilities in the chiral-nematic state of CNCs.
Highlights
Various applications of cellulose have been developed, such as alternative ecofriendly thermal insulator materials which consist of aligned nanocellulose fibers [1] and the ion-induced formation of hydrogels and glasses consisting of nematically ordered cellulose nanocrystals [2] using both monovalent and divalent salts [3]
For a cellulose nanocrystals (CNCs) suspension with a concentration of 5 wt % without added salt, plots of the measured normalized intensity autocorrelation functions for various values of the wave vector as obtained from the SAeDLS setup in the VH mode and for the wide-angle dynamic light scattering (DLS) setup in the VH and VV modes are given in Figs. 3(a)–3(c), respectively
Dynamic light scattering on CNC dispersion relations have been performed at small wave vectors in order to probe the relaxation of long-wavelength density fluctuations
Summary
Various applications of cellulose have been developed, such as alternative ecofriendly thermal insulator materials which consist of aligned nanocellulose fibers [1] and the ion-induced formation of hydrogels and glasses consisting of nematically ordered cellulose nanocrystals [2] using both monovalent and divalent salts [3]. The anisotropic shape of cellulose nanocrystals [commonly abbreviated as (CNCs)] gives rise to a chiral-nematic phase at sufficiently low ionic strengths where in the optical pitch is reported to depend on the ionic strength [4,5]. The length of individual cellulose nanocrystals is on the order of a few hundreds of nanometers, resulting in chiral-nematic domains with sizes of a few microns.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
