Liquid crystal added electrorheological fluid

Abstract

Electrorheological (ER) fluids are a class of materials whose rheological properties are controllable via the application of an external electric field. Without the presence of an electric field, the ER fluid exhibits Newtonian fluid behavior. However, when an electric field is applied to an ER fluid, its rheological response demonstrates Bingham characteristics. Since a typical ER fluid consists of a suspension of fine dielectric particles in a dielectric liquid, this ER behavior is considered to stem from polarization of the particles and the resultant structural change [1–3]. In order to obtain the polarization of the suspended particles, the dielectric constants of both the particles and the liquid medium must be different with the dielectric constant of the particles being typically higher than that of liquid. When an electric field is applied, a mutually interacting force occurs among these polarized particles, which form chains and aggregate to form thick columns bridging the two electrodes [4]. Increasing the ER effect is a natural way to improve the yield stress since the shear stress is related to the rate of change for the electric energy density with respect to the shear deformation. This rate of change depends mainly on the particle structures formed in an external electric field and the energy density of the ER fluids. When the structures are the same, the energy densities increase at a given electric field either by a increasing the mismatch between the dielectric constants of the particle and the carrier fluids or additives [5]. Although there exist reports of many particledispersed ER fluids, their practical utilization has been limited due to particle sedimentation, aggregation or solidification; particle or electrode abrasion; poor durability; and temperature dependence [6]. Low molar mass liquid crystals (LC) [7], lyotropic polymeric liquid crystals [8], and ferroelectric polymer solutions [9] have been proposed as alternative materials to resolve these problems. Compared to wet-base ER materials, in which the particles contain small amounts of moisture, various anhydrous systems, including zeolite [10] and conducting polymers such as polyaniline and its derivatives [11–14], poly(acene guinone) radicals [15], poly(p-phenylene) [16], polypyrrole [17], polymer/clay nanocomposites [18–20], and phosphate cellulose [21],