Abstract
A cellulose nanocrystal (CNC) suspension can form liquid crystal films with unique self-assembly behaviors. This gives CNC films a special iridescence, which has potential in many aspects, but the brittleness of pure CNC films limits their application. In this work, we propose a simple physical mixing method to obtain CNC film by adding D-sorbitol as a plasticizer. We first found that low D-sorbitol content (less than 6 wt% in CNC/DS composite solution) did not make a significant difference compared with pure CNC films in optical performance and, at the same time, the mechanical properties of the CNC films were improved. The various low contents of D-sorbitol can be well dispersed in CNC aqueous suspension, and the wavelength of the selectively reflected phenomenon is relatively stable and slightly decreased at 5 nm for concentrations from 0 to 6%. This phenomenon is opposite to that generally reported, where the wavelength of the selective reflected phenomenon increases obviously with the increase in plastic content. The pitch of the chiral structure decreased from 406 to 362 nm with an increase in D-sorbitol concentration. When the content of D-sorbitol reached 4%, the tensile strength, elongation at break, and Young modulus increased to 39.9 Mpa, 3.00%, and 2.99 GPa, respectively.
Highlights
Liquid crystals (LC) can be regarded as a mesophase
We controlled the content of sorbitol in Cellulose nanocrystals (CNC)/DS composite solution below 6 wt%, and we found that sorbitol can improve the flexibility and tensile strength of CNC films without destroying the self-assembly behavior of CNC
It can be observed that pure CNC films have obvious cracks and breakage, whereas CNC/DS2 and CNC/DS3 films have few cracks
Summary
Liquid crystals (LC) can be regarded as a mesophase. They exhibit some degree of isotropy, like a liquid, and can maintain the order of crystal in at least one direction, so anisometric molecules only have orientation order but not position order [1]. The LC assembly behavior results in corresponding optical properties [2], and they show chiral or achiral structures in nature [3,4,5,6]. The CNC suspension can selfassemble to form left-handed chiral liquid crystals when it reaches a certain critical concentration [15,16]. This helix structure can be maintained in the dried film through the slow evaporation of water [17]. It is important to overcome this shortcoming, while maintaining its optical properties
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