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We measured the homogeneous nucleation rates of D2O in a supersonic nozzle. Small angle neutron scattering (SANS) experiments characterized the nanodroplet aerosols and yielded the number density N of particles formed. In these new SANS measurements the number densities were in the range of 4×1011

Small angle neutron scattering (SANS) experiments were used to characterize binary nanodroplets composed of D2O and H2O. The droplets were formed by expanding dilute mixtures of condensible vapor in a N2 carrier gas through a supersonic nozzle, while maintaining the onset of condensation at a fixed position in the nozzle. It is remarkable, given the small coherent scattering length density of light water, that even the pure H2O aerosol gave a scattering signal above background. The scattering spectra were analyzed assuming a log-normal distribution of droplets. On average, the geometric radius of the nanodroplets rg was rg=13 (±1) nm, the polydispersity ln σr was ln σr=0.19 (±0.07), and the number density N was N=(2±0.2)⋅1011 cm−3. The aerosol volume fractions derived from the SANS measurements are consistent with those derived from the pressure trace experiments, suggesting that the composition of the droplets was close to that of the initial condensible mixture. A quantitative analysis of the scattering...

We examined the condensation of H2O, D2O, and four intermediate mixtures (20, 40, 60, and 80 mol % D2O) in a supersonic nozzle. Because the physical and chemical properties of protonated and deuterated water are so similar, this system is ideal for studying the change in condensation behavior as a function of condensible composition. In our experiments dilute mixtures of condensible vapor in N2 are expanded from three different stagnation temperatures resulting in a broad range of onset temperatures (190–238 K) and pressures (27–787 kPa). For a fixed stagnation temperature, the partial pressure required to maintain the onset of condensation at a given location or temperature in the nozzle is consistently higher for H2O than for D2O. In contrast, the supersaturation at fixed onset temperature is usually higher for D2O than for H2O and this difference increases toward lower temperature. The partial pressure at onset for the intermediate mixtures varied linearly between the values observed for the pure compo...

Very recently, Wolk and Strey [J. Phys. Chem. B 105, 11683 (2001)] presented empirical temperature correction functions for calculating homogeneous nucleation rates J of H2O and D2O (1

We present data from the first systematic studies of binary condensation in supersonic nozzles. The apparatus used to conduct the experiments is described in detail, and the important issues of stability and reproducibility of the experiments are discussed. Experiments were conducted with water, ethanol, propanol, and binary mixtures of these compounds. Onset was determined in the temperature range of 190–215 K, and for each mixture composition the pressures of the condensible species at an onset temperature of 207 K were determined. For the ideal ethanol–propanol mixtures, the onset pressures at constant temperature vary almost linearly between those of the pure components. In contrast the isothermal onset pressures for the nonideal water–ethanol and water–propanol mixtures lie below the straight line joining the pure component values. This large reduction in the total pressure of condensible at onset for the aqueous alcohol mixtures is indicative of a strong mutual enhancement in the particle formation process.