Static and dynamic light scattering from polyelectrolyte microcrystal cellulose

This work describes the static and the dynamic properties of fractionated microcrystal cellulose whiskers using elastic and quasi-elastic light scattering techniques. These colloidal particles have been obtained by acid hydrolysis from raw materials (tunicate, a marine animal) that lead to stable aqueous suspensions. The presence of charges along these rod-shaped particles induces a structural order in these suspensions, This has been highlighted, using light scattering, by the existence of several scattering peaks in the structure factor S(q) = 1(q)/P(q) as a function of the wavevector q. We have studied the static structure factor as well as the autocorrelation functions as a function of whisker concentration, C (2.6 x 10(-3) to 1.3 x 10(-2) g/cm(3)) and ionic strength (1 x 10(-6) to 1 x 10(-5) mol/L NaCl). In the absence of added salt, salt-free suspensions, the observed maxima, that are due to the electrostatic interactions, depend on the whisker concentration C and scale roughly as C-1/2. These maxima disappear progressively as the ionic strength is increased. At high ionic strength, the intensity scattered by these charged colloidal particles increases and reaches neutral system behavior, before the suspension flocculates. All these properties are found also in the dynamic behavior where the measured effective diffusion coefficient Gamma(q)/q(2), at low ionic strength, presents minima and maxima as a function of q and, as expected, is found to be inversely proportional to S(q).