Levitated drops of water containing dispersed 1-octadecanol particles were evaporated into a flowing gas stream Evaporation and resulting shrinkage of the drop collected the 1-octadecanol at the drop surface, concentrating the 1-octadecanol to surface densities more than ten times those needed for a phase change in Langmuir trough experiments, before the appearance of the solid (S) surface phase was observed. When acidic species were introduced into the aqueous substrate, this delay was reduced, and for initial pH values less than or equal to 4, the S phase of 1-octadecanol appeared at surface densities predicted from Langmuir trough data, i.e. no delay was observed. Ionic species in pH neutral substrate also speeded the phase change, but less markedly. The addition of NaOH further retarded the phase change at a concentration of 2 x 10(-4) M but exhibited no effect at 2 x 10(-5) M and lower concentrations. The effect of each ionic species added to the substrate on S phase formation was also concentration dependent, being most pronounced at initial concentrations above 1 x 10(-4) M, and indistinguishable from pure water below approximately 4.0 x 10(-7) M. Light-scattering measurements on the experimental mixtures showed that 1-octadecanol in aqueous mixtures exists as small ( < 400 nm radius) particles.