Effects of ionic strength on the isotropic-chiral nematic phase transition of suspensions of cellulose crystallites

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 KCI) concentrations. A chiral nematic phase formed when the suspension concentration was higher than 5.14 x 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.