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 result ing failure of the ER fluid. In order to reduce the power demand at a parti cular field, the current drawn by the fluid must be reduced. The emeraldine hydrochloride form of polyaniline is unsuitable as an ER sub strate due to its high conductivity (10(-1) S cm(-1)) and resulting high cu rrent 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 su rface of polyaniline. The redox induced initiation of various monomers of i nsulating polymers was investigated by reaction of the monomers at the surf ace 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 relate d to the oxidation state of the initial film. The electrochemical experiments have been repeated using bulk chemical cond itions 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 contr olling 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 insulati ng polymers passed less current at particular applied electric fields, howe ver, these samples also demonstrated polarisation-saturation phenomenon und er high field strengths (> 2400 V mm(-1)). (C) 2001 Elsevier Science B.V. A ll rights reserved.