Electrohydrodynamic Stability of Space-Charge-Limited Currents in Dielectric Liquids. II. Experimental Study

Abstract

Electroconvective effects are being studied in films of dielectric liquids, using an electron beam as an injecting electrode. The experiments are performed on a dual electron beam system in which one beam is used to charge up the free surface of a thin layer of the liquid, the other beam is directed across the surface and is used to determine the surface potential of the sample. The conduction properties of a silicone fluid (Dow Corning 703) have been determined, using this system. At low currents the conduction is space-charge-limited. Above the critical voltage, V0 = 99μη/ε, the space-charge-limited conduction becomes unstable; cellular convection motion of the liquid occurs, and there is a transition between space-charge-limited conduction and convection-enhanced conduction. Thus, the conductivity of the liquid increases due to the bulk motion of the fluid. A further effect of convection can be seen in the charging transients. For low values of current the voltage follows a charge-up curve which is characteristic of a space-charge-limited capacitor. For larger currents a well-defined peak occurs in the charging curves and this is indicative of a change in the conduction properties of the fluid. The time delay from current onset to the onset of convection has been measured as a function of current, for several sample thicknesses. These time delays are in close agreement with theoretical values calculated from a heuristic model of transient stability in space-charge-limited current flow.