Electrification Associated with Breakup of Drops at Terminal Velocity in Air

Abstract The electrification accompanying the breakup of large drops falling in air in the absence of an electric field has been studied. A closed circuit vertical tunnel has been used, and the chemical composition of the drops has been carefully controlled. The results obtained for the average charge separation between the large and small fragments are non-specific regarding the nature of the ions present (except for surface-active species), but strongly dependent on the electrolytic conductivity. The magnitude of the effect goes from about +10−2 esu per breakup (5 × 10−2 esu cm−3) for pure water to −10−2 esu for concentrated solutions, reversing sign at about 10−5 Ω−1 cm−1 (concentrations ∼10−4 N). It was shown that these results can be interpreted on the basis of two competing processes, one of which is the shelling of the electrical double layer on the water–air interface while the air develops the characteristic liquid film bag or bubble.