Rheological properties and material characteristics of field-responsive fluids

Abstract

In this thesis, experimental studies on the field-responsive fluids were performed in terms of the development of novel materials and characterization of the rheological properties. The field-responsive fluids are representative smart materials having electric or magnetic field-dependent properties induced by the patterned structures in the external field. Among them, electrorheological (ER) and magnetorheological (MR) fluids can offer a potential applicability in development of a novel device as a fast, reversible mechanical-electrical interface. However, the performance of ER and MR fluids should be further improved along with the fundamental understanding of related mechanisms. Therefore, major objective of this thesis is placed in the understanding of the relation between the material properties and microscopic/rheological behavior of these fluids. As a novel ER material for the high temperature application, semiconductive polymeric particle suspension is prepared. In order to investigate the effects of the electrical properties of polymeric particles on the ER phenomena, conductivity of semiconductive poly(p-phenylene) particle is controlled. The dielectric behaviors of ER suspension revealed facilitated interfacial polarization for the suspension with intermediate conductivity of particle. These behaviors were closely related with the magnitude of dynamic yield stress, which showed a maximum and then decreased with increasing the conductivity of particles. Therefore, we established an optimum condition of particle conductivity showing the maximum ER activity. In order to promote the ER effect considerably, a novel multiphase dispersion system has been designed and investigated. Here the dispersed emulsion drop is introduced to the polyaniline particle suspension with optimum conductivity. The electrical conductivity of emulsion drop (Celeclor s45) was $10^2$ times higher than that of medium (silicone oil), so that this emulsion itself showed ER activity...