Nematic ordered cellulose properties

The structure of cellulose is closely tied to its synthesis, and although many of the chapters discuss the synthesis of cellulose, the nature of the cellulose product is always kept in mind. A comprehensive account of the structure of cellulose and its polymorphism is provided by French and Johnson, and the structure and properties of a novel form of cellulose (nematic-ordered cellulose) is described by Kondo. Cellulose is the most abundant biomacromolecule in nature, and it is used in a variety of applications. In almost all cases, the applications of cellulose as an industrial material are dependent on its physical and chemical properties. Two chapters discuss novel applications of cellulose. Czaja et al. describe the use of microbial cellulose for applications in wound care and Kim discusses the usefulness of cellulose as a smart material, specifically the production of cellulose-based electroactive paper. 

The authors developed a unique form of i-glucan association, nematic ordered cellulose (NOC) that is molecularly ordered, yet noncrystalline. NOC has unique characteristics in particular, its surface properties provide with a function of tracks or scaffolds for regulated movements and fiber production of Acetobacter xylinum (=Gluconacetobacter xylinus), which produces cellulose ribbon-like nanofibers with 40-60 nm in width and moves due to the inverse force of the secretion of the fibers (Kondo et al. 2002). This review attempts to reveal the exclusive superstructure-property relationship in order to extend the usage of this nematic-ordered cellulose film as a functional template. In addition, this describes the other carbohydrate polymers with a variety of hierarchical nematic-ordered states at various scales, the so-called nano/micro hierarchical structures, which would allow development of new functional-ordered scaffolds. 

Revol, J.-F. (1998). Solid films of cellulose with chiral nematic order and optically variable properties,/. Pulp Pap. Set, 24,146-149. 

Gray DG (1994) Chiral nematic ordering of polysaccharides. Carbohydr Pol5fm 25(4) 277-284 Greiner A, Hou H, Reuning A, Thomas A, Wendorff JH, Zinunermami S (2003) Synthesis and opto electronic properties of cholesteric cellulose esters. Cellulose 10(l) 37-52 Habibi Y, Lucia LA, Rojas OJ (2010) Cellulose nanocrystals chemistry, self-assembly, and applications. Chem Rev 110(6) 3479-3500... 

Cellulose and its derivatives have the ability to behave both as thermotropic and lyotropic liquid crystals. As mentioned above, several specific phases of liquid crystals occurs, depending on the structure or combination of molecules. In the nematic phase, the molecules have only orientational ordering (making the liquid crystal phase less ordered), while in the smectic phase, the molecules have both orientational and positional ordering [75]. In addition, the optically active molecules can form a chiral nematic phase (or cholesteric phase). In this case, the molecules are helix-oriented generating some spectacular optical properties. 

The optical properties of the nanofibers are highlighted by the fact that when the crystals in aqueous suspension reach a specific concentration, they tend to form an ordered chiral nematic phase. Above this critical concentration aqneons suspensions present birefringence characteristics [42], This feature was observed by authors such as Siqueira et al. [63] and Viet et al. [82] in the CNCs obtained from golden grass (capim donrado) and cotton fibers, respectively. In Figure 13.9 it is possible to observe the birefringence characteristics of these cellulose whiskers suspensions obtained from the literature. 

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