The measured isoelectric points of the bubbles were consistently very close to the isoelectric points of the free amine or free acid precipitate, which appear in alkaline solutions for amine and in acid solutions for fatty acids.This indicates the electric charge of bubbles in such systems results from the armoring of bubbles by the partially hydrophobic surfactant precipitate.Registry No. Dodecylamine hydrochloride, 929-73-7; lauric acid, 143-07-7; sodium oleate, 143-19-1; sodium dodecyl sulfate, 151-21-3; sodium dodecanesulfonate, 2386-53-0.

Two light-scattering techniques have been applied to study the kinetics of droplet evaporation and attendant interfacial phenomena. The first technique, which is particularly useful for noisy data, utilizes the fast Fourier transform of phase function data (intensity vs. scattering angle) to obtain the size by comparing the phase function with LorenzMie theory. The second method applies optical resonance measurements to obtain very precise measurements of size and/or refractive index as functions of time. The techniques have been used to measure the slow evaporation of multicomponent and single-component organic microdroplets, rapid evaporation of water droplets, and rapid evaporation of droplets of aqueous solutions and surfactant solutions. The experiments were performed in an electrodynamic balance, which was used to suspend single microdroplets in a polarized laser beam. Rapid evaporation rate data yield information on the surface temperature, and data for surfactant solution evaporation show that insoluble monolayer formation at the microdroplet surface reduces the evaporation rate by a factor of 200. In addition, it is shown that droplet explosion due to surface charge effects can occur well below the Rayleigh limit of charge.

No abstract

No abstract

No abstract