Electrorheological fluids based on chitosan particles

Abstract

Electrorheology (ER) is concerned with the effect of an applied electric field on the flow of fluids, including a sharp increase in shear viscosity and exhibition of a yield stress. Typical ER fluids are suspensions of polarizable particles dispersed in insulating oils [1]. Under an imposed electric field, the viscosity increases drastically, and the suspensions may even become solidlike due to induced particle dipoles. Furthermore, all the physical and mechanical property changes are virtually reversible as soon as the applied electric field is switched off [2]. The formulation of ER suspensions with optimal properties to control ER effects is determined by a number of factors such as particle concentration, particle size and size distribution, and electric and dielectric properties. Conventional fluids require active substrates, such as water [3], surfactant [4] and glycerin [5]. However, the main disadvantage of the water-activated systems is their limited temperature range [6]. Viscous and conductive heating of the fluid also causes waterloss, which results in a decrease in the fluid effectiveness. Furthermore, the presence of substantial amounts of water could lead to dielectric breakdown, corrosion, and high power consumption. Novel dry-base ER systems composed of inorganic and polymeric materials [7–9] possess several advantages and have been studied to meet the requirements of a broad working temperature range, reduced abrasion, and a relatively low current density. Examples include carboneous particle [10], zeolite [11, 12], and various polymer semi-conductors, such as acene quinone radical polymers [13, 14], poly(p-phenylene) [15], polyaniline [16–18], polyphenylenediamine [19], and copolyaniline [20, 21]. Recently, organic-inorganic hybrid particles, such as polyaniline-clay nanocomposite [22], polyaniline coated silica particle [23] and SANclay nanocomposite [24, 25], have also been adopted as materials for dry-base ER fluids. It is noted that these synthetic organic polymers possess either branched polar groups, such as amino, hydroxy, and amino-cyan, or repeated semi-conducting groups. The polar groups may affect the ER performance by acting as electron donors.