Translational and rotational dynamics of rodlike cellulose whiskers

The dynamic properties of suspensions of rodlike cellulose microcrystallites (whiskers) are investigated using polarized and depolarized dynamic light scattering (DLS, DDLS) and transient electric birefringence (TEB). The whiskers were prepared by controlled sulfuric acid hydrolysis from cotton and tunicate cellulose fibers. Translational (D) and rotational (Theta) diffusion coefficients in dilute suspensions were measured. For the cotton system, D = 5.5 x 10(-8) cm(2)/s, Theta(DDLS) = 552 s(-1), and Theta(TEB) = 536 s(-1). With the use of Broersma's relations, the rotational and translational diffusion coefficients lead to values of the length L = 255 nm and the cross-section diameter d = 15 nm. For the tunicate-derived whiskers, D = 1.5 x 10(-8) cm(2)/s, Theta(DDLS) = 11 s(-1), and Theta(TEB) = 14 s(-1). These values and Broersma's relations give L = 1160 nm and d = 16 nm. The DDLS and TEB techniques are in good agreement for the rotational diffusion coefficients, especially for the cotton whiskers. These results provide validation for using DDLS to study the dynamics of cellulose whisker systems in both simple suspensions and complex environments. Cellulose whiskers may thus be used as model rigid rods dispersible in aqueous suspensions the structure and dynamics of which may be readily studied by widely available techniques.