EFFECTS OF IONIC IMPURITIES ON EHD MOTION AND CONDUCTION IN NONPOLAR LIQUIDS

This paper reports the influence of an anionic surfactant, dodecyl ben zenesulfonic acid on charge injection and convection assisted conducti on in a naphthenic transformer oil, and three paraffinic liquids subje cted to a step voltage. When impurities are present in a liquid they s cavenge the surfactant and reduce its effective conduction; hence the surfactant has less influence on conduction in naphtenic oil than in t he paraffinic liquids. The transient currents in test liquids containi ng surfactant were similar to injection currents with electrohydrodyna mic (EHD) motion rather than to currents due to ionic dissociation. In jection in nonpolar liquids containing an anionic surfactant was contr olled by the charge density at the interface due to adsorption of surf actant molecules and not by true charge injection. Based on the relati on between the delay time t(d) and field E a simple expression of the form C-n = kE(-(2+beta)) has been derived to describe the injection st rength in nonpolar liquids with weak injection. The results show that the beta values for nonpolar liquids with weak injection range between -0.90 and -1.32 which are significantly different from the beta = -2 value for polar liquids with strong injection. Also, the steady state current I-33 varied as I-33 = k'E(alpha) with alpha < 2. Hence conduct ion in naphtenic and paraffinic solvents is considered electrode limit ed and not space charge limited.