(649b) Brownian Particle Coagulation in a Rapidly Expanding Solvent; Example of the “Allowable” Coupling Between Homogeneous Kinetics and Fluid Dilation Rate

Using recently studied supercritical ?anti-solvent? (SAS-) examples for precipitating high-value particles (eg., pharmaceuticals) we suggest1 that the characteristic dilation time [(1/vol)*D(vol)/Dt]^-1 of the swelling solvent can be deliberately made small enough to noticeably reduce the operative coagulation rate ?constant?, beta. Moreover, we expect that this previously neglected coupling can occur under conditions in which post-nucleation Brownian coagulation must be accounted for in predicting the efficacy of such micron-sized powder production methods. A rational approximate theory for this rate constant ?correction factor?, beta/beta(0), is proposed1 -------summarized here, with emphasis on the applicable limit of continuum Brownian diffusion-controlled coagulation. We also present a preliminary assessment of the PSD-implications of these ?corrections?, and indicate possible generalizations. Note that, while P. Curie's principle applied to an isotropic medium of arbitrary EoS does NOT preclude coupling between homogeneous (chemical,?) rate processes and local fluid dilation rate (trace of Def(velocity vector)), this may be the first practical example of such a coupling------ with consequences that can be exploited in the processing of pharmaceutical powders. __________________________________

a Supported at Yale University by NSF Grant CTS 0522944 1. Rosner,DE and Arias-Zugasti M, AIChE J, vol 56 (in press, 2010)