Reaction engineering principles in materials synthesis and design - I am working with students and collaborators to develop chemical reaction engineering and design principles for a class of materials whose properties rely on molecular structure direction from solution. For instance, in network polymerization, small molecules dissolved in solution are caused to knit together in three dimensions to form a metastable solid structure.
The processes we are currently addressing are:
1) sol/gel ceramic synthesis and hybrid inorganic/organic polymer synthesis,
2) radiation-induced crosslinking of polymer coatings, and
3) templating of and shape selective placement and motion in zeolite frameworks.
Each of these projects is motivated by engineering and materials needs of the coming decades. Each process as currently performed is more an art than an exact science; we are submitting them to reaction engineering analysis. Sol/gel techniques are providing materials with designer properties - optical, electronic, mechanical, and surface chemical - and there is compelling economic interest to truly engineer these materials as well as traditional polymers. Photo-induced crosslinking is currently used to make exceptionally tough, stable, and impermeable glassy polymer coatings without the use of volatile organic solvents, but the principle challenge is to avoid excessive buildup of stress. The placement and motion of guest molecules in frameworks such as those of zeolite crystals is responsible for the performance of most catalysts and sorbents used today, but quantitative non-empirical optimization, design, and control of these structures and properties is just being developed. Materials reaction engineering has much in common with classical reaction engineering - the principal difference is that the product is a solid and the selectivity being sought has to do with the molecular structure of the solid. The reaction engineering approach is taken - we identify and use key characterization techniques (usually spectroscopy, frequently nuclear magnetic resonance) to monitor reaction kinetics and selectivities as functions of design parameters. We supplement these real experiments with computer experiments (simulations) that help us to conceptualize reasons for the process behavior. These concepts lead us to propose models that are used for design. We test these models to ensure that they are predictive over a range of design parameters. Frequently the limits of a model provide instruction about physical chemistry of the reacting system.