Electrorheological properties of chitosan nitrate suspension

Chitosan nitrate (CTS-HNO₃) as an electrorheological (ER) material was synthesized by a simple method. The nontoxic and facile chitosan (CTS) as a substrate of the materials, as well as nitric acid were chosen as starting materials. The ER properties of the suspensions of the CTS and CTS-HNO₃ materials were researched. The CTS-HNO₃ suspension has much better ER performance than the CTS suspension. The ER effect (relative shear stress, τ_r = τ_E/τ₀) of the CTS-HNO₃ suspension (25 wt%) in silicon oil under a dc electric field reached 94 at a shear rate of 14.5 s^-1, which is eight times higher than that of the CTS suspension, where τ_E and τ₀ are the shear stresses at the electric field strengths of 4.2 and 0.0 kV/mm, respectively. The formation of chitosan nitrate helped to decrease effectively the shear stress at zero electric field, and to enhance the ER effect of chitosan material markedly. The influence of the surface energy, conductivity, dielectric constant and dielectric loss tangent on the ER property of the particle materials was investigated, and the results indicate that surface energy played a predominant role. Moreover, the magnitude of the ER effect of the CTS-HNO₃ suspension was closely related to the shear rate. In addition, the chitosan nitrate had better thermal stability. The properties of CTS-HNO₃ are advantageous in its application as an ER material.