Operation of a variable saturation condensation particle sizer with 2-propanol, ethanol, methanol, and propylene glycol: Resolution and delay time versus volatility

Abstract

The variable saturation condensation particle sizer (VSCPS) of Gallar et al. (2006) determines a condensation (Kelvin) diameter by scanning over the saturation ratio at fixed instrument temperatures, sample flow rate, and total sheath flow rate. This is achieved by mixing a saturated and a dry stream while scanning over the dry/wet flow rate ratio. Previous studies with this VSCPS have used n-butanol and Fluorinert™ FC-43. A slightly modified form of the instrument is tested here with polyethylene glycol particles 3–9 nm in diameter and four working fluids: Propylene Glycol (PG), 2-propanol, ethanol, and methanol. The latter three give steep activation curves (FWHM∼ 2 %). However, this steepness depends on the quality of the bipolar electrospray used to produce monodisperse seed particles. Nevertheless, methanol yields the narrowest activation curves at all sizes studied, especially the smallest ones. All liquids tested except methanol show a widening of the activation curve at diminishing particle diameters, in qualitative agreement with classical heterogeneous nucleation theory with perfect wetting. The response time depends strongly on working fluid volatility (7.8 s for PG; 1.2 s for methanol), apparently due to the time required to dry the condensate film deposited on the wall of the thermal insulator separating the saturator from the condenser.