The Green Group

Department of Chemical Engineering

The Green Group

Welcome to the Green Group website!

Overview

The primary mission of the Green Research Group is to establish ourselves as leaders in the formulation of advanced nanocomposite materials. It is far simpler and more cost effective to create new materials from existing components assembled in innovative systems. These new materials have the potential to exhibit enhanced mechanical, optical, thermal, or electrical properties depending on their formulation. Future applications of this research include the automotive, aerospace, product packaging or medical industries. The overarching theme of our fundamental studies is to elucidate and quantify how polymers at interfaces control the actions of hard nanoparticles and soft polymer droplets, in polymer solutions, melts, and blends.

The current research spans a wide variety of standard chemical engineering topics including interfacial phenomena, surface engineering, thermodynamics, mass transport, fluid dynamics, reaction/synthesis engineering, and statistical mechanics. By borrowing theory and techniques from these areas, the Green group is able to forge connections within the field that have not previously been exploited.

 

There are five major thrust areas that transcend all research within the Green group.

Surface/Interface Engineering

When creating dispersions and nanocomposites, the surface interactions control the overall functionality of the system. To make nanoparticle dispersions in polymer melts, polymer chains can be grafted to the surface of colloidal particles. The stability of the dispersion will then be governed by the strength of the interactions between the surface chains and the surrounding matrix. Dispersions of immiscible polymer blends are formulated using block or graft copolymers, which diffuse exclusively to the interface between the two immiscible phases. The presence of the copolymer allows previously immiscible components to become a uniform dispersion. Study of the surface mechanisms and interactions of dispersed systems will lead to enhanced fundamental understanding of these systems.

 

Reaction Engineering and Synthesis 

Controlled reaction schemes are essential to creating well-defined colloidal systems.  In our lab, we use sol-gel synthesis to grow monodisperse metal oxide nanoparticles.  By adjusting reaction parameters, we control nucleation and growth to obtain a desired size, distribution and number density of nanoparticles. We also use reaction engineering to modify the surfaces of the nanoparticles.  Living radical polymerization techniques are currently being implemented to control the chain length (molecular weight) and graft density (number per surface area) of polymer chains grown directly from reaction sites on the nanoparticle surfaces.  Using these techniques, high grafting densities can be achieved.  Also, esterification and grafting reactions are used to end-tether premade polymer chains at low to moderate graft densities.

 

Characterization

A number of techniques are used to characterize various properties of our systems. To determine the size of our particles, dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used.  By analogy, optical microscopy is used to determine the droplet size distribution in our liquid systems.  In order to quantify the composition, graft density, molecular weight of chemisorbed polymers on particle surfaces, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), gas chromatography (GC), nuclear magnetic resonance (NMR) spectroscopy and elemental analysis are employed. These techniques allow us to quantify key parameters in our systems.  Furthermore, static light scattering (SLS), DLS, as well as small- and ultra-small angle x-ray scattering (SAXS and USAXS) are used to characterize aggregation or stability of nanoparticles in simple and complex solutions.

Complex Fluids 

The presence of long chained molecules in fluid systems will commonly induce significant deviation from small molecule simple solutions (solvents) on mass and momentum transfer properties.  Our research investigates the rich behavior of liquid polymers in the both presence and absence of solvent, commonly called polymer solutions and melts.  We explore the gamut of polymer concentration regimes from dilute regime to semi-dilute to concentrated to the melt.  By studying how solvent-polymer interactions affect colloidal stability, we gain insight into the fundamental mechanisms occurring in dispersions.

 

Rheology

Rheology is simply the study of deformation and flow of matter. Since the fluids utilized in experimental systems are complex, sophisticated measures must be used to characterize them. A central idea in this discipline is that different morphologies respond differently to induced flow, stresses, or strain. In this way, it can be used to distinguish and characterize morphology present in experimental systems.  Our stress-controlled rheometers can run a multitude of rheological experiments with several geometries. This equipment can test systems ranging from low viscosity polymer solutions to high viscosity pure polymer melts.