Breakdown and buildup mechanisms of cellulose nanocrystal suspensions under shear and upon relaxation probed by SAXS and SALS

Abstract

Highlights The structure of CNC suspensions under shear was studied by rheo-SAXS and SALS. A broad range of lengthscales from nanometer to micrometer has been explored. Changes in cholesteric organization and disappearance of pitch under shear have been evidenced. The CNC organization over the three-regime rheological behavior has been clarified. Buildup mechanisms, from nematic to cholesteric were highlighted on large scales.

Orientation of Cellulose Nanocrystals Controlled in Perpendicular Directions by Combined Shear Flow and Ultrasound Waves Studied by Small-Angle X-ray Scattering

“…This complexity could be associated to the acoustic pressure effect needed to firstly disrupt the cholesteric organization of the CNCs initially existing at rest, and then to induce the orientation of the isolated CNCs until reaching a parallel arrangement in a stable nematic organization. concentration, 44 the PCA Anisotropy value at high shear flow of 1000 s -1 was about 0.45, which is higher than the one reached in this work under US (0.25). For comparison an equivalent PCA Anisotropy value of about 0.25 (the one achieved under US) was reached under flow at shear rate of 5 s -1 , 44 which gives the order of magnitude of an equivalent shear rate induced by US, if one consider US radiation as a streaming phenomena.…”

“…concentration, 44 the PCA Anisotropy value at high shear flow of 1000 s -1 was about 0.45, which is higher than the one reached in this work under US (0.25). For comparison an equivalent PCA Anisotropy value of about 0.25 (the one achieved under US) was reached under flow at shear rate of 5 s -1 , 44 which gives the order of magnitude of an equivalent shear rate induced by US, if one consider US radiation as a streaming phenomena. 4,5 After a high shear flow of 1000 s -1 and upon the cessation of this high shear that induced a complete dissociation of the CNCs, it was evidenced a kinetic of relaxation up to 700 s. 44 In this case, the relaxation time corresponded to a decrease of the PCA anisotropy at nanometer scale (calculated from 2D SAXS patterns), and a simultaneous increase in viscosity.…”

“…SAXS data from diluted suspensions at rest, assuming a parallelepipedal shape for the sonicated CNCs, gave 121 × 20 × 5 nm 3 average dimensions. 15,44,54 Shear flow/US-Cell. A Shear flow/US-Cell composed of a parallelepipedic channel containing an immersed vibrating blade was developed to, on one hand, apply shear flow and/or ultrasonic waves to the feed suspensions and, on the other hand, to monitor in situ the dynamical structural organization changes by SAXS.…”

“…The effect of several external solicitations on the CNC structural organizations have been extensively studied in the literature. This includes shear flow field, [9][10][36][37][38][39][40][41][42][43][44] magnetic field, 45,49 electric field, 29 surface tension in drying processes, 19,20,50,51 and pressure forces in membrane separation processes. [52][53][54] More specifically, the effect of shear flow on the structural organization of CNCs have been extensively explored from a fundamental 9,10,36-41-44,51,54-56 to an industrial point of view in several processes inducing a flow.…”

Shear-Coated Linear Birefringent and Chiral Cellulose Nanocrystal Films Prepared from Non-Sonicated Suspensions with Different Storage Time

“…Region II is found at intermediate shear rates where a plateau in viscosity is ascribed to disruption of tactoids into smaller units and release of CNC to some extent. Region III is located at higher shear rates where another shear-thinning zone reflects the breakdown of tactoids and the alignment of the individual CNC in the direction of the applied shear [ 17 , 32 ]. In Figure 3 , the viscosity profile of the sample with 120 days of storage shows characteristics of the liquid crystalline phase identified by the plateau below shear rate 1 s −1 (region II) and the shear-thinning behavior at higher shear rates (region III).…”