Cellulose nanocrystals in aqueous suspensions: rheology of lyotropic chiral liquid crystals
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A thorough rheological study of the behavior of cellulose nanocrystals (CNC) in water was undertaken, focusing on the main characteristics of rod-like suspensions that allign under flow and can display liquid crystal behavior at rest, in at least a range of concentrations. The effect of adding a dispersing agent (gum arabic, GA) to the suspension was analyzed, and different surface treatments were also performed on the CNC using TEMPO, chloro(dodecyl)dimethylsilane and trimethoxysilyl propylmethacrylate, named as TCNC, DCNC and MCNC respectively. The CNC, TCNC and the suspensions prepared with added GA formed stable suspensions with a concentration range in which isotropic and anisotropic (self-organized) phases coexisted in equilibrium. On the other hand, the aqueous suspensions of the two silanized CNCs only displayed flow-induced ordering, with a similar type of rheological behavior to the other nanocrystal suspensions, although with obvious quantitative differences. These latter ones were not stable suspensions and precipitated after a few hours of rest. The rheological tests included steady shear, dynamic oscillations and start-up of steady shear that were performed for all the nanocrystals suspensions prepared at different concentrations. Differences observed were related to the crystals surface modifications or addition of the dispersing agent. A persistent periodic oscillation of the viscosity was measured in the start-up of steady shear tests and the periods of the oscillations were determined and related to the different types of crystals considered.
KeywordsCellulose nanocrystals Liquid crystals Rheology Tumbling Viscosity
The authors acknowledge the funding from ANPCyT (PICT 162034) and UNMdP (15/G494-ING500/17). J.M. Buffa thanks CONICET for a doctoral fellowship.
- Beekmans F (1997) Rheology and changes in structure of thermotropic liquid crystalline polymers. Technische Universiteit Delft, DelftGoogle Scholar
- Mewis J, Wagner NJ (2012) Colloidal suspension rheology, 1st edn. Cambridge University Press, New YorkGoogle Scholar
- Narimissa E, Rahman A, Gupta RK, Kao N, Bhattacharya S (2014) Anomalous first normal stress difference behavior of polymer nanocomposites and liquid crystalline polymer composites. Polym Eng Sci 47:21–25Google Scholar
- Rahman A (2013) Rheology of thermotropic liquid crystal polymers for injection moulding. Royal Melbourne Institute of TechnologyGoogle Scholar
- Xu T (2014) Inorganic nanocylinder lyotropic liquid crystals: rheology, phase behavior and film self-assembly. Ph.D. thesis, Auburn University. https://etd.auburn.edu/handle/10415/4072
- Xu T, Davis VA (2015) Rheology and shear-induced textures of silver nanowire lyotropic liquid crystals. J Nanomater 2015:9Google Scholar