Coating of a semi-conducting polymer for use in electrorheological fluids

The power demand of an electrorheological (ER) fluid has a direct effect on the running costs of an ER device, the onset of field breakdown and resulting failure of the ER fluid. In order to reduce the power demand at a particular field, the current drawn by the fluid must be reduced. The emeraldine hydrochloride form of polyaniline is unsuitable as an ER substrate due to its high conductivity (10(-1) S cm(-1)) and resulting high current and power demand. However, polyaniline can be used as an effective ER substrate when in its 'insulating' emeraldine base form (10(-9) S cm(-1)). This can be achieved by polymerising insulating vinyl monomers onto the surface of polyaniline. The redox induced initiation of various monomers of insulating polymers was investigated by reaction of the monomers at the surface of polyaniline modified electrodes held at potentials corresponding to distinct oxidation states of polyaniline. The results of these experiments show that the coating of polyaniline with vinyl monomers is directly related to the oxidation state of the initial film. The electrochemical experiments have been repeated using bulk chemical conditions as ER fluids require the substrates to be in the powdered form. The oxidation state rather than degree of protonation was found to be the controlling factor of the coating reaction. Electrorheological measurements of synthesised fluids have been carried out using a static yield test rig. Samples which had been coated with insulating polymers passed less current at particular applied electric fields, however, these samples also demonstrated polarisation-saturation phenomenon under high field strengths (> 2400 V mm(-1)). (C) 2001 Elsevier Science B.V. All rights reserved.