Design of polymeric substrates for controlled molecular crystallization
Author(s)
Diao, Ying, Ph.D. Massachusetts Institute of Technology
DownloadFull printable version (22.51Mb)
Other Contributors
Massachusetts Institute of Technology. Dept. of Chemical Engineering.
Advisor
Bernhardt L. Trout and T. Alan Hatton.
Terms of use
Metadata
Show full item recordAbstract
It is essential to control crystallization in many areas of science and technology, such as the production of pharmaceuticals, pigments, concrete, semiconductors, as well as the formation of biominerals. In most practical circumstances, crystallization starts with heterogeneous nucleation at a foreign surface. Despite its widespread occurrence, mechanistic understanding of the role of a surface in heterogeneous nucleation is limited, especially in a solution environment. My thesis aims at elucidating the roles of surface chemistry and nanostructure on nucleation to enable rational design of surfaces for controlling crystallization from solution. To this end, I systematically investigated the role of surface chemistry, morphology, in particular porous structures of various polymeric materials on heterogeneous nucleation using small organic molecules as model compounds. I have demonstrated quantitatively the significance of surface chemistry to nucleation kinetics using a variety of polymer surfaces. By tuning the surface composition of the polymers, aspirin nucleation was promoted by up to an order of magnitude compared to the bulk. Further mechanistic investigations revealed that, macroscopically, it is through interfacial free energies that the surfaces influence the surface nucleation activity. Equipped with nucleation induction time statistics as a powerful tool, I found that nanoscopic pores of 50-100 nm accelerated nucleation by up to two orders of magnitude compared with surfaces without pores. Moreover, I demonstrated for the first time that the shape of surface nanopores is essential in determining the nucleation behavior, using lithographic methods for nanopatterning the polymer films. A molecular mechanism was further proposed based on additional mechanistic investigations. Furthermore, the nanoconfinement effect on nucleation was studied using polymeric microgels with tunable nanostructures and chemistry, whose mesh sizes range from 0.7-2 nm. We presented the first experimental evidence for the existence of an optimum confinement size at which the rate of nucleation was dramatically enhanced by up to four orders of magnitude. The degree of nucleation enhancement depends on the extent of polymer-solute interactions, whose role was elucidated from the perspective of adsorptive partitioning and nucleation-templating effect. In addition, the microgel nanostructure was also shown to play an important role in determining the crystal polymorphism of pharmaceutical compounds.
Description
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2012. Cataloged from PDF version of thesis. Includes bibliographical references (p. 171-175).
Date issued
2012Department
Massachusetts Institute of Technology. Department of Chemical EngineeringPublisher
Massachusetts Institute of Technology
Keywords
Chemical Engineering.