The effect of a polymeric additive on the evaporation of organic aerocolloidal droplets

 The evaporation of single triethyl phosphate (TEP) micro-droplets containing a high molecular weight polymer, poly(methyl methacrylate) (PMAA), was inves-tigated using an electrodynamic trap and light scattering measurements to explore the suppression of evaporation by the additive. Pure-component evaporation rates were measured to determine the vapor pressure over a range of temperatures, and the polymer was found to significantly decrease the evaporation rate. A numerical solution of the problem of simultaneous solvent evaporation and polymer diffusion within the droplet indicated a rapid build-up of PMMA at the surface of the drop, but vapor/liquid thermodynamic considerations alone do not account for the observed reduction in the evaporation rate for the droplets containing PMMA. After significant evaporation of TEP occurred, the ultra-low evaporation rate was measured using changes in the Raman spectra associated with morphology-dependent resonances. The evaporation in this regime appears to be controlled by the rate of solvent molecules diffusing through the polymer matrix. Received: 17 June 1997 Accepted: 24 October 1997