Michael P. Anisimov

Correlations for Vapor Nucleating Critical Embryo Parameters

Condensation nucleation light scattering detection in principle works by converting the effluent of the chromatographic separation into an aerosol and then selectively evaporating the mobile phase, leaving less volatile analytes and nonvolatile impurities as dry aerosol particles. The dry particles produced are then exposed to an environment that is saturated with the vapors of an organic solvent (commonly n-butanol). The blend of aerosol particles and organic vapor is then cooled so that conditions of vapor supersaturation are achieved. In principle, the vapor then condenses onto the dry particles, growing each particle (ideally) from as small as a few nanometers in diameter into a droplet with a diameter up to about 10 μm. The grown droplets are then passed through a beam of light, and the light scattered by the droplets is detected and used as the detector response. This growth and detection step is generally carried out using commercial continuous-flow condensation nucleus counters. In the present res...

n-Pentanol–helium homogeneous nucleation rates

An international collaboration to examine the effects of different experimental systems on nucleation measurements has resulted in a series of nucleation experiments on the n-pentanol–helium system. In particular, using a laminar flow diffusion chamber, nucleation rate data were obtained for temperatures between 258 and 266 K and total pressures of 0.10, 0.20, and 0.30 MPa. These results are compared with other data on nucleation measured experimentally using an expansion wave tube, a two-piston expansion chamber, a flow diffusion chamber, and a static diffusion chamber. The influence of the carrier gas pressure on nucleation rates was explored. It was concluded that the critical embryo phase transitions should be detectable in an analogous manner to the recently reported phase transitions in the glycerin–carbon dioxide system. The experimental detection of the melting point is suggested as a critical test for the ability of an experimental system to provide adequate measurements of nucleation rates. For ...

Relationship of phase diagrams and surfaces of new phase nucleation rates

Experimental and theoretical investigations of vapor nucleation began about 100 years ago. Until the 1980s, experiments generally measured only critical supersaturation values. Since then, measurement procedures have substantially improved and nucleation rates can now be measured as a function of temperature, vapor activities, and pressure with high accuracy. Nucleation theory has made obvious progress, but the understanding of nucleation phenomenon is far from complete. New approaches to conceptualizing nucleation are necessary in order to identify possible new directions for further improvement of nucleation theory. One such approach is the analysis of the topology of nucleation rate surfaces. The creation of a nucleation rate surface is based on knowledge of phase equilibrium diagrams, limited experimental nucleation results, and a few plausible assumptions. In this article, the surfaces of the nucleation rates as a function of pressure or activity for single and binary systems for nucleation from meta...

Binary N-octanol–sulfur hexafluoride nucleation

Recently, the accuracy of vapor nucleation rate measurements has increased substantially. However, when experimental conditions become close to the values to the critical parameters of investigated systems, significant discrepancies were found between the experimental results and theoretical predictions. Some studies have found agreement between results and theory only within a narrow range of nucleation conditions. Therefore, it is appropriate to investigate the nucleation of additional systems to obtain new information to guide nucleation theory development. Alcohols are the most studied class of chemical compounds, but currently there are no experimental data on n-octanol vapor nucleation. The present study is devoted to the investigations of the homogeneous nucleation of the n-octanol in sulfur hexafluoride. Comparison of the critical pressures for binary mixture with the Laplace pressure calculated in the droplet approximation using the bulk liquid surface tension shows that the carrier gas has a mor...

General Requirements and Recommendations for Vapor Nucleation Rate Experiments

Agreement between experimentally measured vapor nucleation rates and current theoretical predictions exists for only a limited number of systems. These inconsistencies can result from differences in measurement methods and assumptions used to interpret the experimental results. Usually the causes of these disagreements are unclear. The current state of the art is such that experimental results using different methods can lead to very different interpretations of the same phenomenon. In this note, well-defined standard systems are suggested as a means to verify experimental system performance. The combination n-pentanol-helium is suggested as a standard reference system. Using this system, measurements produced by multiple research groups have been compiled, and from these experimental results, a nucleation rate equation was developed that can serve as a standard basis for method comparison. This equation provides a scale to relate nucleation rates over a range of nucleation temperatures and is a useful basis of comparison even if the proposed equation is not fully accurate. It is further suggested that the nucleation rate measurements be performed using small steps in nucleation temperature of around 2 or less to identify the features in the system such as phase changes in the critical embryos. In this note, a method that uses monotonicity and continuity conditions for the nucleation rate surface to detect such singularities is outlined. These monotonicity and continuity criteria can be formulated as a dimensionless quantity. The semiempirical construction of nucleation rate surfaces can indicate conditions where multiple nucleation rate surfaces may be detected. Experimental systems that include size distribution measurements have the potential to discern particles produced through multiple nucleation channels such that nucleation rates can be measured for each channel. Detection of nucleation rate surface singularities is important because these singularities indicate the existence of two-channel nucleation where one-channel nucleation theory cannot be applied.

Dynamic state phase diagrams for nucleated systems

In the present research the topological analysis of nucleation rates surfaces based on the nucleation rate surface and the phase diagram relationship is used. The qualitative relation of phase (stable) state diagram behavior with intermolecular interaction is well known in theory of solutions. The dynamic state phase diagrams are introduced and discussed here. Transformation of these diagrams with deviation of system from equilibrium states is considered. It is found in agreement with results of non-equilibrium thermodynamics, that for system moving away from the equilibrium state the molecules are losing individuality and intermolecular interaction becomes interaction similar to the unimolecular system.

Surface Topology of the Ion-Induced Vapor Nucleation Rate

ABSTRACT Ion-induced nucleation involves additional electrostatic interactions between vapor molecules (atoms) and ions. The electrostatic force helps to form the ion stabilized prenucleation embryos and lowers the free energy barrier for nucleation. The free energy for ion-induced critical embryos formation has been calculated using the Thomsons term in the framework of the classical theory of nucleation. Nucleation theory has made obvious progress, but the understanding of the nucleation phenomenon is far from complete. Some ideas for the identification of possible new directions to improve both homogeneous and heterogeneous nucleation theories can be found by analyzing the topology of nucleation rate surfaces. The creation of the ion-induced nucleation rate surfaces is based on the knowledge of phase state diagrams, experimental results on ion-induced nucleation, and a few plausible assumptions. In this article the surfaces of the ion-induced nucleation rates for metastable vapor nucleation will be co...