Baron Peters earned his B.S. and M.S. from the University of Missouri and his PhD from the University of California-Berkeley.

Dr. Baron on simulating nucleation and poly-morph selection.

Dr. Peters introduced three main subjects of this study: Polymorphism, Mitosis, and Laser Induced Nucleation.  Polymorphism was described in terms of Stranski and Totomanov’s theories on nucleation. Mitosis centered on the interfacial free energy that must be overcome in order to promote growth.  Lastly, laser induced nucleation was introduced as a new study on the effects of optical Kerr on nucleation.

Classical nucleation theory estimates the interfacial free energy barrier to nucleation by treating the phase nuclei as the core surrounded by metastable liquid. Dr. Peters stated his challenge was finding a method for calculating the free energy at a nano-scale and maintaining a constant chemical potential in the transition phase of nucleation.  To Dr. Peters, this means determining the appropriate strategy through an anecdotal or mechanistic insight. His approach leans towards a mechanistic view of polymorph selection in which Brownian dynamics and the Yukawa potential are the key to identifying and promoting solid nuclei clusters.

In studying mitosis, he found that the free energy landscape has only one channel towards polymorphism rather than two as traditionally believed. This posed the question that if there is only one channel, how do we get two polymorphs? Dr. Peters states that from an unstable liquid the polymorph nuclei takes the fastest route to stability depending on its particle content and energy level of its interfacial free energy barrier. Using a 2D-steady Smoluchowski model with a 2D-Kramers crossover the polymorphic pathway can be determined due to the particle dynamics of nucleation size overpowering the selection.  Dr. Peters used two methods for estimating the free energy. The traditional approach involves the use of the Frenkel Defect but leads to large scale calculations for each particle insertion.  Therefore, Dr. Peters states he is using umbrella sampling for explicit solvent systems in lattice form from which he can monitor the structure of the polymorph.  This gives him a base for adding particles to change the polymorphic structure.

Not all polymorphs undergo nucleation within a reasonable time frame and some need weeks to undergo nucleation. This is where Dr. Peters proposed laser-induced nucleation.  Discovered by Myerson and Garetz, laser-induced nucleation expedites solid nuclei clusters into a metastable phase through the optical Kerr effect. Dr. Peters’ hypothesis on the effects of optical Kerr is that the laser’s wave frequency is too fast to orient the chemical potential of the solvent. However, the induced electric field torque of the laser aligns the poles of the nuclei clusters fast enough to promote crystallization.  His computational method involved the development of hybrid Potts lattice gas models to describe the two steps of nucleation under the semi-grand canonical Monte Carlo form. To test his hypothesis, Dr. Peters used sparking water as his solvent.  With the laser he examined the optical Kerr Effect on the carbon dioxide molecules and observed crystallization occur in a medium that would otherwise not undergo nucleation.  He believes the Kerr Effect promoted bubble formation along the laser light which in turn caused crystal nucleation.  Questioning the results, does the absence of absorption bands imply non-photochemical nucleation?  Dr. Peters continues to study this subject to provide a concrete answer.  In concluding this presentation, Dr. Peters touched upon the importance of thermo, dynamics and specific size metrics in nucleation and polymorph selection.  His research is funded by NSF and the Los Alamos National Laboratories.

For further reading consider the following:

• Paper: Progress On Polymorph Selection: Structure Specific Coordinates and Dynamics of Structure Formation by Baron Peters, Chemical Engineering, UC Santa Barbara, Santa Barbara, CA
• Journal: Towards Multiscale Modeling in Product Engineering by Zdzislaw Jaworski, Barbara Zakrzewska, Computers & Chemical Engineering, Volume 35, Issue 3, 8 March 2011, Pages 434-445
• Journal: Molecular Mechanism for the Cross-Nucleation between Polymorphs by Caroline Desgranges and Jerome Delhommelle, Journal of the American Chemical Society 2006 128 (32), 10368-10369