Determination of ultra-low vapor pressures by submicron droplet evaporation

Abstract

Vapor pressures as low as of order 10−8 mm Hg (10−10 atm) have been determined by measuring the diffusion-controlled evaporation rates of single submicron droplets suspended in an electric field in the path of a laser beam. Using Mie theory to ascertain the droplet radius as a function of time from light-scattering data, the vapor pressures of dioctyl phthalate (DOP), dibutyl sebacate (DBS), and dibutyl phthalate (DBP) have been determined at temperatures near room temperature. In addition to vapor pressures, heats of vaporization and Lennard-Jones molecular interaction parameters are determined from the experiments.