The formation of ordered phases of acid-hydrolyzed cellulose suspensions was studied as a function of cellulose crystallite concentration and added electrolyte (HCl, NaCl, and KCl) concentrations. A chiral nematic phase formed when the suspension concentration was higher than 5.14 × 10-6 nm-3 in water. For biphasic samples, the cellulose concentrations in both isotropic and anisotropic phases increase with the total suspension concentration and with added electrolyte. The experimental results were compared with the predictions of the theory of Stroobants, Lekkerkerker, and Odijk for the phase separation of charged rods. The suspensions were not stable at electrolyte concentrations sufficiently high to allow complete evaluation of the electrostatic contribution to the interparticle interactions, but the general behavior was in line with theoretical predictions. The chiral nematic pitch of the anisotropic phase decreased with increasing crystallite concentration and with added electrolyte concentration. Apparently, a decrease in double layer thickness increases the chiral interactions between the crystallites.

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Stable colloidal suspensions of cellulose crystallites with negatively charged sulfate groups on their surface were prepared by acid hydrolysis of filter paper. The suspensions, which were free of added electrolyte, formed chiral nematic ordered phases above a critical concentration. A sharp boundary was observed between coexisting chiral nematic and isotropic phases, enabling measurements to be made of the relative amounts of each phase as a function of total cellulose concentration. The isotropic-to-chiral nematic phase equilibrium was sensitive to the nature of the counterions present in the suspension. Samples were prepared with sodium, potassium, cesium, ammonium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, trimethylammonium, and triethylammonium counterions. Suspensions with H+ counterions formed an ordered phase at the lowest concentrations of crystallites. For inorganic counterions, the critical concentration for ordered phase formation increases in the order H+ < Na+ < K+ < Cs+. For the organic counterions, the critical concentration in general increases with increasing counterion size, suggesting that the equilibrium is governed by a balance between hydrophobic attraction and steric repulsion forces. The nature of the counterions also influences other properties of the suspensions, such as their stability, the temperature dependence of the phase separation and of the chiral nematic pitch, and the redispersability of dried samples made from the suspensions.

Stable colloidal suspensions of rodlike cellulose crystallites, prepared by acid hydrolysis of cellulose fibers, form a chiral nematic phase above a critical concentration. The direction of the chiral nematic axis may be controlled by applying a strong magnetic field. In the presence of Congo red, a dye with strong affinity for cellulose, the suspensions show induced circular dichroism (ICD) at the dye absorption wavelengths, indicating that the dye molecules are in a chiral environment. The isotropic suspension shows a relatively weak positive ICD peak, while the chiral nematic phase shows a very strong negative ICD peak when viewed along the chiral nematic axis. The peak is weaker for unaligned chiral nematic samples and is very small when viewed at right angles to the chiral nematic axis. Thus the ICD in the chiral nematic phase results from the orientation of the dye molecules in a chiral nematic array. The ICD band intensity increases with chiral nematic pitch.