Mustafa YAVUZ, Halil İbrahim ÜNAL

Electrorheological properties of suspensions prepared from poly (Li-tert-btyl methacrylate) ionomer

The synthesis, characterisation and partial hydrolysis of poly(tert-butylmethacrylate), (PTBMA), and the electrorheological (ER) properties of its suspensions were investigated. The polymer was syn-thesised by radical polymerisation and partially hydrolysed by para-toluenesulphonic acid monohydrate (PTSA.$H_2O$), and then converted to a lithium salt (PTBMA-Li) by washing with a $LiOH_{(aq)}$ solution. Prom particle size measurements, the average particle size of PTBMA-Li was determined to be 74 $mu$ m. Colloidal suspensions of ionomer were prepared in various insulating oils [silicone oil (SO), mineral oil (MO), threeoctylthreemellitate (TOTM) and dioctylphatalete "(DOP)] at a series of concentrations (c = 5-33 m/m, %). The sedimentation stabilities of these suspensions were determined at 20 °C and were observed to increase with decreasing suspension concentration. Maximum gravitational stability was observed as 32 days in SO at c = 5 m/m, %. Flow times of suspensions were measured under no applied electric field (E = 0 kV/mm) , and under an external electric field (E $neq$ 0 kV/mm) , and ER activity was determined. The highest flow time was found to be 32 s in SO at c = 33 m/m, %. Further, the effects of solid particle concentration, shear rate $(gamma)$, electric field strength, (E) addition of polar promoters and high temperature on the ER activities of colloidal suspensions were investigated. Excess shear stresses $(Deltatau)$ were determined to be 74 Pa under E = 1.0 kV/mm.

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