Formation of Perfluoropolyether Coatings by the Rapid Expansion of Supercritical Solutions (RESS) Process. Part 2:  Numerical Modeling

Abstract

The rapid expansion of supercritical solutions (RESS) process is a promising method for the production of ultrafine powders and aerosols of narrow size distribution for coatings and other applications. In this article, part 2 of a two-part study, the nucleation and subsequent growth of 2500 M w perfluoropolyether diamide (PFD) from supercritical carbon dioxide (CO2) by expansion through a small-diameter nozzle is modeled in a three-stage, multidimensional fashion. The stages include a hydrodynamic solution, solvent−solute phase equilibria analyses, and an aerosol transport model. The hydrodynamics model successfully captures the vapor−liquid transition that occurs as carbon dioxide is expanded to ambient conditions. Cloud-point pressures and equilibrium compositions of the separated solvent−solute system are determined and are used in a multidimensional aerosol transport model. This model incorporates various mechanisms influencing droplet growth. Parametric studies are conducted to investigate the influences of the interfacial tension, the equilibrium addition of carbon dioxide, and the diffusion coefficient on the predicted droplet diameter. Turbulent coagulation in the ambient region downstream of the expansion nozzle is found to be the dominant mechanism responsible for the production of micron-sized droplets observed in companion experiments.

Polymer Chain Collapse in Supercritical Fluids. 2. Experimental Evidence

“…For the polyisobutylene mixtures (see Figure 7) the tendencies are similar than à Parameters S-L of PDA [104] Copyright ß 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.ms-journal.de those obtained from molecular simulation. However, the deviations are larger considering the C values.…”

“…4). Several experimental techniques such as the IGC (Inverse Gas Chromatography), [85][86][101][102][103][104] intrinsic viscosity measurement, density measurement are commonly used.…”

Deagglomeration of nanoparticle aggregates via rapid expansion of supercritical or high‐pressure suspensions

“…Additionally, a constant value was assumed for the friction factor in the momentum equation, as has been done in many studies. 40,43,44,53,[62][63][64] In reality, however, the friction factor would depend on the flow rate, and thus, would be a function of position. Moreover, in the free expansion, the 1D flow approximation would not be applicable.…”

“…The RESS/REHPS process has been modeled by many researchers in the literature; for example, refer to Debenedetti, 40 Reverchon and Pallado, 43 Franklin et al, 53 Hirunsit et al, 54 Khalil and Miller, 55 and Weber and Thies. 45,46 Therefore, only a skeletal description of the model is presented here and the analysis is limited to conditions close to those employed in our experiments.…”

Precipitation Technologies for Nanoparticle Production

“…Aspirin ( For needle-shaped particles: length/diameter; For spherical particles: diameter; Nonspherical refers to particles that do not possess an aspect ratio typical of needle-shaped particles, but deviate signifi cantly from an aspect ratio of unity (i.e., rectangle with aspect ratio ~2 drug solubilities and thus increase supersaturation and nucleation rates (Liu and Nagahama 1996 ) , the higher temperatures also tend to increase turbulence within the mixing chamber, leading to higher instances of particle coagulation (Franklin et al 2001 ) . The increased rate of particle coagulation appears to outweigh the benefi ts of enhanced nucleation rates achieved by elevated T pre-exp conditions.…”