NUCLEATION

Basic Studies of Nucleation

Heterogeneous Nucleation Initial experiments were conducted using the original turbulent mixing CNC system (Mavliev and Wang, 2000; Mavliev et al., 2001). Supersaturation was controlled by means of changing the DBP vapor pressure in nozzle flow by saturating only a predetermined part of the flow while the total flow and temperature remain constant. This approach allows changing the initial DBP vapor pressure while keeping the flow structure and temperature field unchanged. The DBP concentration in the outlet of the vapor generator was measured experimentally for different ratios of saturated and bypass flows and found to be close to estimated values. Experimental results for transitions from heterogeneous nucleation to homogeneous nucleation are presented for NaCl and WOx particles at various DBP vapor pressures. With increasing of the DBP vapor pressure, the concentration of enlarged particles increases until it reaches a plateau. At higher initial values of DBP pressure, homogeneous nucleation prevails and the number concentration of particles follows a curve typical for homogeneous nucleation recorded in the absence of nuclei. Nuclei with different mobility diameters were activated at different values of vapor pressure. There are significant differences in the slopes of particle activation curves for NaCl and WOx particles. The reasons for such differences are a subject for the continuing research of this project and studies continue at this time. These results have been presented and published by Mavliev et al. (2001). This work largely completes the work on the nucleation of dibutylphthalate on various substrates. A new and improved turbulent mixing CNC has been designed, constructed, and studied. We made side-by-side tests of two identical units to ensure that the parallel measurements made at IIT and Clarkson would be comparable. We made a series of measurements of nucleation of additional vapor compounds on a series of different composition nuclei at both schools. Nucleation for all of the vapors have been measured for NaCl, silver, and carbon particle particles. These results have prompted some limited additional studies on related solid substrates such as KCl and AgCl. We have experimentally measured the contact angle for most of the combinations of the vapor compounds on the various substrates. These data were then used in interpreting the results of the nucleation measurements.

Vapor Substance

Nuclei Substance

Dibutylphthalate(DBP)

NaCI

Octodecane

Ag

Octadecanol

C

Octadecanoic Acid

KC1 and AgC1

At IIT, heterogeneous nucleation of working fluids' vapor on NaCl, Ag, KCl, and AgCl was examined. Three different patterns of nucleation and growth were observed. In the case of octadecanoic acid, all of the nuclei were activated and could then grow as they accumulated vapor. The activation of these nuclei did not appear to be dependent on the composition of the nucleus. For octadecane, octadecanol, and DBP, a bimodal pattern was observed for all of the nuclei except the case of octadecanol on NaCl. In this case, some nuclei activate and grow while the remaining particles keep their initial size distribution. In the case of octadecanol with NaCl, a second mode only slightly larger than the initial size distribution forms in the presence of even small amounts of vapor. When the partial pressure of octadecanol reaches a sufficiently high value, some of the nuclei activate into a grown mode. It appears nucleation occurs on both of the smaller modes in equal proportion as the relative intensity of the two smaller modes remains unchanged as the vapor concentration is increased. These results were submitted to the Journal of Chemical Physics. In order to more fully interpret these results, a theoretical model was developed. They outline of this model was developed by Vladimir Smorodin and this work is being prepared for publication. At Clarkson, experimental heterogeneous nucleation of the working fluids' vapor on carbon particles was measured. Experimental nucleation rates from these results were calculated and, then, compared to the estimated nucleation rates based on Fletcher's heterogeneous nucleation theory. This theory matches well with the experiments with octadecanol and octadecanoic acid, and at high supersaturation ratio for DBP. However, the theory shows discrepancy with the observed phenomena at low supersaturation for dibutyl phthalate, and, especially, for octadecane. Hydrophilicity of functional groups of working fluids was considered as an important factor. Several other possible hypotheses related to physico-chemical properties of carbon particles and working fluids' vapor for the discrepancies in heterogeneous nucleation and observed particle growth are discussed in Lee et al., 2003).

Homogeneous Nucleation: We are also examining the influence of pressure on homogeneous nucleation of vapors. Prior work has suggested that there are effects of both the composition and pressure of the support gas on the rate of homogeneous vapor nucleation. However, there is no theoretical basis for the observed effects. Thus, additional experimental work is needed to better understand the nature of this effect.

The List of Recent Publications is as follows:-

  • Use of a Turbulent Mixing CNC to Study the Influence of Composition and Vapor Properties on Heterogeneous Nucleation, P.K. Hopke, D.W.Lee, Rashid Mavliev, and Hwa-Chi Wang, In:  Nucleation and Atmospheric Aerosols, B. Hale, and M. Kulmala, eds., American Institute of Physics, AIP Conference Proceedings 534, pp.139-142 (2000).
  • Improvement of the Homogeneous Nucleation Rate Measurements in a Static Diffusion Chamber with Use of a CCD Camera, V. Zdímal, J. Smolík, P.K. Hopke, and J. Matas, In: Nucleation and Atmospheric Aerosols, B. Hale, and M. Kulmala, eds., American Institute of Physics, AIP Conference Proceedings 534, pp. 311-314 (2000).
  • n-Pentanol-Helium Homogeneous Nucleation Rates, M.P. Anisimov, P.K. Hopke, S.D. Shandakov and I.I. Shvets, J. Chem. Phys. 113:1971-1975 (2000).
  • A Transition from Heterogeneous to Homogeneous Nucleation in the Turbulent Mixing CNC, R. Mavliev, P.K. Hopke, H.-C. Wang, and D.-W. Lee, Aerosol Sci. Technol. 35: 586-595  (2001).
  • Two Channel Vapor Nucleation in the Vicinity of the Triple Point, L. Anisimova, P.K. Hopke, and J. Terry, J. Chem. Phys. 114:9852-9855 (2001).
  • Binary N-Octanol - Sulfur Hexafluoride Nucleation, M P. Anisimov, P. K. Hopke, I.N. Shaimordanov, S. D. Shandakov, and L.-E. Magnusson, J. Chem. Phys. 115: 810-816 (2001).
  • Nucleation Rate Surface Topologies for Binary Systems, M.P. Anisimov and P.K. Hopke, J. Phys. Chem.  B; 105:11817-11822 (2001).
  • General Recommendations For Vapor Nucleation Rate Experiments, M.P. Anisimov,  P.K. Hopke, and Z.N. Esina, Aerosol Sci. Technol.  37:183-186 (2003).
  • Comparison of Experimental and Theoretical Heterogeneous Nucleation on Ultrafine Carbon Particles, D.-W. Lee, P.K. Hopke, D.H. Rasmussen, H.-C. Wang, R. Mavliev, J. Phys. Chem. B  107: 13813-13822 (2003).
  • Characteristics of Nucleation and Growth Events of Ultrafine Particles Measured in Rochester, NY, C.-H. Jeong, P.K. Hopke, D. Chalupa, M. Utell, Environ. Sci. Technol. 38: 1933 - 1940 (2004).
  • Experimental Studies of Heterogeneous Nucleation in the Turbulent Mixing Condensation Nuclei Counter, R. Mavliev, P.K. Hopke, H-C Wang, D.-W. Lee,  J. Phys. Chem. B 108: 4558-4564 (2004).
  • Condensation Activation and Nucleation on Heterogeneous Aerosol Nanoparticles, V.Y. Smorodin and P.K. Hopke, J. Phys. Chem. B 108: 9147-9157 (2004).

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