Alon McCormick, Fellow

Modeling of Linear Viscoelasticity; Molecular Scale Chemical Reaction Engineering of Materials Synthesis; Visualization of Sorbates in Zeolite Pores

Free-radical polymerization of multifunctional monomers such as (meth)acrylates lead to the formation of highly crosslinked polymer networks. These networks have found applications in coatings, films, information technology, and other areas. However, such crosslinking polymerization exhibits special features that are not observed in linear polymerization. These features include unequal reactivity of pendant and monomeric functional groups, microgel formation, and structural heterogeneity. To characterize these features, this group is developing a lattice percolation model.

The microscopic structure of a linear viscoelastic material is mechanically equivalent to a network of linear viscous and elastic elements. The elements considered in this analysis are “springs” that represent elastic deformation, and “dashpots” that represent viscous-like changes in the stress-free state. Each element is joined at each of its two ends to one or more other elements. The node-element incidence matrix method is used to model the force balance in the network. An incidence matrix is defined which incorporates the connectivity of the entire network. The equation governing the stress development is then given by a differential algebraic equation (DAE), which can then be solved to obtain changes in the stress state of the system with time. The model’s results have provided valuable insight into viscoelasticity in a network.

A network of springs and dashpots can also be used for modeling curing coatings. The liquid monomer is represented by a network of dashpots. As the reaction in the network takes place, a dashpot is replaced with a spring as bonds start forming. Thus, elasticity in the network builds up as the network cures. The goal is to study the evolving viscoelasticity in the curing coating and to track the stress development. This model will be combined with the kinetic gelation modeling described above. This will also allow the group to optimize the curing process in order to maximize the conversion and minimize stress.

Studies have also been started to understand wrinkling of coating surfaces. This will involve modeling of stress in the coating and some instability studies for the coating surface.

Molecular simulations have been a potent tool in studying the behavior of molecules in nano-confined spaces—in small- and mediumpore zeolites, for example. They have been used to study mobility of the molecules, their adsorption dynamics, and separations based on the above-mentioned behavior, all of which may be very different from what one would expect from their bulk properties. In the past, simple spherical molecules or those that could be approximated reasonable as spheres were studied. This group has begun to look at aromatics, a set of molecules with complex geometry, to learn about their packing behavior, mobility, and adsorption dynamics using molecular dynamics and Monte Carlo simulations.

The group used simulations of adsorption of shaped molecules in zeolite pores of different types to identify certain principles of shape selectivity. The next step in this research will be to study how shaped molecules diffuse differently in zeolite pores. The group hopes to be able to use the results of these studies to develop separation techniques for these compounds —a very important, economically-driven need for the petroleum and petrochemical industry. Also, the group hopes to learn enough from this research to develop a technique for economical, good separation of similar compounds used by the pharmaceutical and specialty chemical industries.

Research Group

Soumendra Basu, Graduate Student Researcher
Joseph J. Miller, Undergraduate Student Researcher
Sanat Mohanty, Graduate Student Researcher
Vijay Rajamani, Graduate Student Researcher
Diane M. Vaessen, Research Associate
Mei Wen, Graduate Student Researcher