## Research Abstracts Online

January
2008 - March 2009

### University of Minnesota Twin Cities

Institute of Technology

Department of Chemical Engineering and Materials Science

## PI: Alon V. McCormick, Fellow

### Molecular-scale Chemical Reaction Engineering of Materials Synthesis

These researchers use Galerkin’s method with finite element basis function (GFEM) to calculate viscoelastic stress generation for curing coatings. During solidification, the stress-free state of the coating changes, causing shrinkage. Along with this, the physical properties transition from viscous fluid to hard elastic solid. Adhesion to a solid substrate frustrates shrinkage in the coating plane and can lead to residual elastic stress. To calculate how the material behaves, equations of momentum conservation and a constitutive equation must be combined and solved simultaneously. Computer calculations allow researchers to "look inside” coatings as the cure properties or substrate geometry changes, allowing results that are impossible to measure physically. Such information will help optimize the curing process and shine light on defect formation mechanisms.

Another project concerns master equation analysis of kinetic cluster growth. Cluster growth has been traditionally described with Classical Nucleation Theory (CNT), which approximates the net growth as monomer addition and evaporation. The addition of monomer is approximated by assuming a hard sphere gas kinetic collision rate and monomer evaporation is calculated through detailed balance. These assumptions lead to predictions of the particle growth rate that are at best several orders of magnitude different from experimental values. This project seeks to model cluster growth through the formalism of unimolecular reaction rate theory and weak collision theory, taking into full account the energetics of cluster-monomer collision and the redistribution of that energy within the internal structure of the newly formed cluster. The growth and decay rate constants obtained from collision analysis will then be used in a kinetic Monte Carlo simulation to model cluster growth in a variety of settings that are of industrial, environmental, and academic importance.

### Group Members

Chongai Kuang, Graduate Student

Daniel J. O’Neal, Graduate Student