Conjugated polymers as active components of electrorheological fluids

ER properties of suspensions of four conjugated polymers - polyaniline, polyphenylene, polythiophene and pyrolysed polyacrylonitrile - in relation to their electric properties and chemical nature were studied. The polymer samples were synthesized and characterized by various methods and flow curves of their mixtures with silicone oil were recorded under electric field. It was found that the ER activity resulted from surface polarization processes due to presence of polar species (polyaniline and pyrolysed polyacrylonitrile) or bulk polarization related to mobile ions (polyphenylene). Polythiophene, despite its conjugation, showed only residual ER effect. The main conclusion is that many conducting (conjugated) polymers exhibit ER activity but the most characteristic and important feature of these materials - the conjugated system of multiple bonds - does not seem to be responsible for that. The electronic conductivity resulting from the conjugation contributes to higher currents which is unfavourable for technical applications. Conjugated polymers are ER active due to the enhanced mobility of ions within the bulk of particles dispersed in a liquid matrix and/or polar groups present on their surface.