Aspects of surface cleaning in dense carbon dioxide: Micron scale particle removal and mass transfer in micelle systems.

摘要

Particle removal and micelle additives are important new areas of research into precision cleaning with near-critical carbon dioxide. Precision cleaning is an important step in the processes such as silicon chip manufacture, micro electronics, and medical sterilization. This study develops a particle adhesion model that incorporates the effect of high pressure on micron-sized particles, and describes the mass transfer characteristics of a micelle-modified CO ₂ system.; The particle adhesion model includes the presence of a fluid layer on the surface and is descriptive of particulate adhesion in precision cleaning applications. The model is applied for an idealized system of graphite/ n-tetradecane/stainless steel at both low and high pressure, and calculations predict that high pressures (as would be required for liquid or supercritical CO₂ cleaning) both increase the particle surface separation distance and decrease the net adhesion force. Experimental data under dynamic conditions validate the theoretical analysis. The data is analyzed to de-couple any effects of changing solvent properties on the particle removal, and results show that increasing system pressure can decrease the minimum required removal force for particles.; Micelle-modified CO₂ systems are important because of their ability to solubilize heavy organics and polar compounds like proteins. Such research has focused on the phase equilibria to determine what chemical properties lead to surfactants that will form micelles in CO₂. The mass transfer in CO₂-micelle systems is relatively unstudied. Accurate descriptions of mass transfer properties are essential to design any processes based on this technology. This study also examines the mass transfer in a CO₂ -micelle system using the solvatochromic probe methyl orange. An effective diffusivity model is presented and experimental data from the adsorption of methyl orange onto silica gel provides insight into the fundamental mechanisms of mass transfer.