Co-condensation of nonane and D2O in a supersonic nozzle

Abstract

We study the unary and binary nucleation and growth of nonane-D2O nanodroplets in a supersonic nozzle. Fourier Transform Infrared spectroscopy measurements provide the overall composition of the droplets and Small Angle X-ray Scattering experiments measure the size and number density of the droplets. The unary nucleation rates Jmax of nonane, 9.4 × 10(15) < Jmax /cm(-3) s(-1) < 2.0 × 10(16), and those of D2O, 2.4 × 10(17) < Jmax /cm(-3) s(-1) < 4.1 × 10(17), measured here agree well with previous results. In most of the binary condensation experiments new particle formation is dominated by D2O, but the observed nucleation rates are decreased by up to a factor of 6 relative to the rates measured for pure D2O, an effect that can be partly explained by non-isothermal nucleation theory. The subsequent condensation of D2O is inhibited both by the increased temperature of the binary droplets relative to the pure D2O droplets, and because the binary droplet surface is expected to be comprised largely of nonane. For the one case where nonane appears to initiate condensation, we find that the nucleation rate is about 50% higher than that observed for pure nonane at comparable pv0, consistent with significant particle formation driven by D2O.

The structure of D2O-nonane nanodroplets

“…8 Although the mixed population fits are reasonably consistent with both the SAXS and FTIR data, we are skeptical that such a distribution of droplets can exist in our experiments, since it requires either two nucleation events, or significant droplet break-up to occur. Based on the analysis presented in Pathak and co-workers 23 we only observe one nucleation pulse during co-condensation and in most cases particle formation is dominated either by the nucleation of D 2 O or by the nucleation of nonane. Given the very small relative droplet velocities and the low probability of droplet col-lisions, droplet breakup is also considered to be an extremely unlikely event.…”

“…To fully characterize the properties of the flow we combine the results of axially resolved static pressure and FTIR measurements in an iterative data analysis procedure described in detail in Pathak et al 23 Summarizing briefly, we first measure p along the nozzle axis while the vapor is condensing and for the carrier gas alone. The latter yields the effective area ratio of the dry expansion (A/A*) dry where A is the area of flow and A* is the area at the nozzle throat.…”

Morphology of Liquid–Liquid Phase Separated Aerosols

“…67,70,96 The contact angles predicted from the experimental surface tensions 88,97,98 at 308 K are 23° and 19.4° in the Young and Neumann regimes, respectively, and quite insensitive to temperature (e.g. with the surface tension values at 283 K, Young's equation predicts θ = 26°, and with surface tensions extrapolated to 233 K, it predicts θ = 29°).…”

Overview: Homogeneous nucleation from the vapor phase—The experimental science

“…To do so they adopted the analysis methods used for LFDDs to estimate the characteristic time and used small angle neutron scattering to determine the aerosol number density. Small angle X-ray scattering extended the reach of these experiments to nondeuterated compounds, 60,78,79,81,[169][170][171] and Fourier transform infra-red spectroscopy (FTIR) enabled both multicomponent nucleation rate measurements 171 and freezing studies. [172][173][174] Tunable diode laser absorption spectroscopy (TDLAS) measurements were used to measure the temperature of the flowing gas mixture 175,176 and the concentrations of small condensable molecules in the gas phase.…”

“…In particular, experimentalists are introducing new techniques such as vibrational spectroscopy 56,171,176,249 and mass spectrometry, 193,233,234,[237][238][239][240]244,[250][251][252][253][254][255] combining multiple complementary techniques to generate redundant data with which to test experimental self-consistency, 68,162,175,249 improving the sophistication of models, 74,231 and conducting complementary quantum chemical calculations. 248,256,257 In this section, we present several examples that highlight recent experimental advances.…”