Abstract
Cellulose nanocrystals produced by acid hydrolysis of native cellulose form a well-known chiral nematic liquid crystal phase. The mechanism involved in the formation of chirality has been the subject of a vigorous discussion. The pH and concentration dependence of the phase is studied using cellulose nanocrystal droplets within a silicon oil suspension, which allows for convenient real-time microscale manipulation of phase behaviors and properties. We demonstrate the existence of nematic phases at both low and high pH regions consistent with the Stroobants - Lekkerkerker - Odijk theory. Our results confirm electrostatic interactions play a critical role in controlling the strength of the chirality.
Highlights
Cellulose nanocrystals produced by acid hydrolysis of native cellulose form a well-known chiral nematic liquid crystal phase
Silicone oil plays no noticeable role in the phase behavior itself and Cellulose nanocrystals (CNCs) liquid crystals (LCs) phase behaviors discussed here can be observed in the bulk with no silicone oil present (Fig. 2a–c) or the droplet form (Fig. 2d–f) with same conditions, when the diameter of CNC-silicone oil droplet is above 100 μm[28]
The initial preparation of chiral nematic CNC LC has a pH around 2 after dialysis, and the Zeta potential of CNC LCs is around −26 mV, which is below the threshold for agglomeration in CNC systems[29,30]
Summary
Cellulose nanocrystals produced by acid hydrolysis of native cellulose form a well-known chiral nematic liquid crystal phase. Cotton[12], wood[13], and other higher plants[14,15] allow for the production of CNCs with the average length that can be tuned between 100 nm and 500 nm with high polydispersity depending on the material[16], while bacterial CNCs are typically a few microns long[17] It is more difficult for higher plant CNCs to form nematic phase LCs compared with bacterial CNCs as their aspect ratios are smaller. CNC LCs with tunable pH and fixed concentration showed two nematic phases in low and high pH regions This loss of chirality in CNC LCs corresponds to a reduced Debye length and a mitigated Coulombic repulsion. The effect of electrostatic forces in CNC suspensions was analyzed and experimental results were in accordance with the theoretical analysis
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