Electrorheology of Suspensions of Aluminum Borate Whiskers Bonded with Poly(Ethylene Glycol)

We prepared aluminum borate whiskers/PEG complex powder (PEG 0.5 similar to 5.0 wt%) by freeze-drying aqueous solutions of PEG with whiskers and studied ER properties of suspensions (contains 10 wt% powder). When the external electric field was not applied, the shear stress of complex powder (PEG 0.5 similar to 1.5 wt%) suspensions at low shear rate was higher than that of neat whisker suspensions. The suspension of whiskers with 1.0 wt% PEG showed higher shear stress than that of neat whiskers under dc electric field. However, whiskers with 0.5 wt% PEG showed weaker ER effect than neat whiskers. When electric field is applied to neat whisker suspensions, whiskers comprise highly branched chains between electrodes. It is assumed that attached PEG alters the structure of whisker chains but this effect is weaker than that of engagement of whiskers in case of 1.0 wt% PEG. In addition, ER effect was not enhanced when whiskers and PEG powder are added in silicon oil severally. Thus, bonding whiskers with PEG by freeze-drying is effective to enhance the ER effect of whisker suspensions.