Electrorheology of the suspensions of oblate poly(ionic liquid) ellipsoids

The shape of dispersed phase particles is an important factor that influences the properties of composites and suspensions. Plate-like particles have attracted great attention in the development of high-performance electro-responsive electrorheological (ER) suspensions due to their unique shape. However, how the plate-like shape influence the ER effect remains unclear because very few suitable electro-active particles with different shapes but the same volume and chemical structure are available. This limits the material design. Herein, we prepared oblate poly(ionic liquid) (PIL) spheroids with different plate-like shape parameters (axial ratio, q) by uniaxial thermomechanical squeezing of uniform spherical PIL particles with high ER activity. Because no chemical reaction is involved and identical spherical PIL particles are used as precursor, the oblate PIL spheroids have the same chemical composition and structure, the same particle volume and density, uniform size and shape, leaving the plate-like shape or q as the sole factor influencing the ER effect. Under electric fields, we investigated the ER effect of the suspensions of the oblate PIL spheroids and compared it with that of their spherical and rod-like prolate counterparts. The results showed that the ER effect of the oblate PIL spheroids increases as q decreases. The ER effect of the oblate PIL spheroids with low shape anisotropy is still higher than that of their spherical counterpart. This is different from the behavior of prolate PIL spheroids with low shape anisotropy, which show a lower ER effect than their spherical counterpart. Based on dielectric spectroscopy and microscopic structure observations, we analyzed the mechanism underlying the influence of the plate-like shape on the ER effect and its difference from that of the rod-like shape.