Characterization of Mass Transfer within the Crystal-Solution Boundary Layer of l-Alanine {120} Faces Using Laser Interferometry during Growth and Dissolution

Abstract

Crystallization and dissolution are important processes to consider in drug development as well as many other industrial processes. Many current growth and dissolution models are based on bulk solution properties and do not implicitly consider concentration variation close to the crystal surface− solution interface and how this is mediated by solute diffusive mass transfer. Solution boundary layer thickness and concentration distribution, for the {120} crystal habit face of single crystals of Lalanine in saturated aqueous solutions during both growth and dissolution processes, is measured as a function of super/ undersaturation using a Mach−Zehnder optical interferometer system. Further analysis allows determination of the diffusion coefficient and mass flux within the boundary layer as well as whether the processes are controlled by mass transfer or crystal interfacial kinetics. The measurement of this study revealed that the {120} face was not saturated at its surface during growth or dissolution meaning both processes were somewhat limited by their crystal interfacial kinetics. Growth was limited by crystal interfacial kinetics at all supersaturations to the same degree, whereas dissolution had a mixed dependency on crystal interfacial kinetics and mass transfer at lower undersaturations becoming more limited by mass transfer at higher undersaturations. Boundary layer thickness increased with super/undersaturation but to a lesser degree than the increase in the concentration difference between the crystal surface and bulk solution leading to a higher mass flux of solute molecules through the boundary layer. At the same relative super/undersaturation mass flux of solute molecules was faster during dissolution which was concurrent with its increased surface to bulk solution concentration difference and boundary layer thickness.

Thermodynamic and Kinetic Modulation of Methylammonium Lead Bromide Crystallization Revealed by In Situ Monitoring

“…We note that if we use the bulk concentration and assume that the crystal growth is fully interface-controlled, eq will yield an apparent kinetic coefficient. To obtain the “true” kinetic coefficient, we would need to have an accurate measurement of the surface concentration, which is experimentally challenging to determine. ,, Additionally, understanding the role of additives such as HCOOH in modulating local surface concentrations is nontrivial and will require future experiments. With these caveats in mind, we proceeded to evaluate the growth kinetics of MAPbBr 3 as a function of HCOOH concentration.…”

Automated Growth Rate Measurement of the Facet Surfaces of Single Crystals of the β-Form of l-Glutamic Acid Using Machine Learning Image Processing

“… 25 This has been previously highlighted by Garside and Tavare 37 through their definition of an effectiveness factor and their highlighting of the importance of growth rate dispersion for modeling its influence on crystal size distribution in a crystallizer. An improved understanding of MT has been demonstrated by Nicholson et al 38 who used laser interferometry to characterize the MT within the boundary layer between the bulk solution and the crystal faces during growth and dissolution. 39 …”