Extraction of charged droplets from charged surfaces of liquid dielectrics

Abstract

Charges are extracted from charged liquid-vapor interfaces in a diode semiimmersed in liquid helium or nitrogen at moderate applied electric fields. A sudden onset of positive charge in the case of helium and of either sign in the case of nitrogen is collected in the vapor at a critical field given empirically by E _c = (12.3 ± 0.8) (δϱΣ)^0.28±0.03 kV/cm, where δϱ is the difference between the liquid and gas densities, and Σ is the surface tension. The data are explained by a model in which charged droplets are extracted from the liquid state with a radius of r _c = (3Σ/δϱg)^1/2, where g is the acceleration of gravity. The current noise is peaked at low frequencies, which possibly indicates a correlation between droplets due to surface waves. If charge is prevented from leaking off the surface by appropriate electrodes, the increased surface charge macroscopically lifts the surface before entering the vapor and generates surface waves in one of the modes of the cylindrical cell.