Electrostatic charging and novel applications of atomised liquids

During the atomisation of liquids from pressure-pack dispensers, an electrostatic charge is imparted to the droplets. This is usually small, in the region of 10-5 to 10-8 C.kg-1, and therefore insufficient to affect the behaviour of the droplets. When the charge generated naturally is enhanced to a value in excess of 1 x 10-4 C.kg-1 using the techniques presented in this thesis, the characteristics of the aerosol spray are beneficially modified. Highly charged aerosols have been generated by making modifications to the formulation, valve and actuator of pressure-pack dispensers. This has been shown to augment the current function of some pressure-pack products. Two applications for this technology are investigated: removal of airborne particles by liquid sprays, and improved bioefficacy of insecticide sprays. It has been established that conventional liquid sprays rapidly reduce the concentration of airborne particles, and that this is significantly enhanced when the aerosol is highly charged, particularly for small particles. Particle depletion is believed to result from contact with the liquid droplets, which quickly precipitate onto surfaces. Increased contact between particles and highly charged droplets by electrostatic attraction and space charge effects would enhance depletion. Application of this novel technology to domestic sprays will be of particular benefit in achieving local depletion of particles that become airborne during domestic activities. Highly charged aerosol insecticides demonstrated faster rates of knockdown and higher levels of mortality in houseflies and mosquitoes than conventional sprays. This improved performance is attributed to enhanced dispersion of the aerosol through the test chamber due to space charge effects, and to electrostatic attraction of the droplet to the insects during flight. Use of highly charged domestic insecticide sprays has not previously been considered and would increase spray efficiency, or lead to equivalent bioefficacy with reduced concentration of active ingredients.