• CAMPUS MAP
• DIRECTORIES
• SITE MAP
• HELP
• SEARCH:

Tech Home >> College of Engineering >> ChBE >> Faculty and Staff

J. Carson Meredith

 

Combinatorial Materials Science

Professor Meredith is at the forefront of an emerging field in polymer and materials science. The purpose of Combinatorial or High-Throughput Polymer Science is to accelerate by orders of magnitude the pace and efficiency of discovery and characterization. As indicated in the slide below, the driving force for this change is the advanced and complex multicomponent and multi-interfacial structure in modern materials. A selection of active research projects in this area are listed below.

 

High-Throughput Mechanical Property Measurements

 

 

 

 

 

 

One of the most time-consuming and expensive tasks in polymer materials development is the measurement of mechanical properties, and their correlation with chemical and physical properties. The methods of combinatorial chemistry and high-throughput screening have improved efficiency and lead to major discoveries in drug discovery and catalysis, but these techniques have not been extended into the realm of polymer mechanics.

We have developed a novel high-throughput mechanical characterization apparatus, called HTMECH, illustrated in Figure 1. The goal is not to replace conventional detailed mechanics and fracture measurements, but rather to introduce a new high-throughput mechanical screening tool that allows measurement of hundreds of compositions, temperatures, and strain-rates in as little as a few hours. We couple the mechanical measurements with high-throughput AFM and FTIR measurements to develop structure-mechanical property correlations. Figure 2 shows stress versus strain data forpolyurethanes on a composition-gradient library, where the composition of chain extender is varied. We have demonstrated recently that our HTMECH apparatus, although very different in deformation mode and scale from conventional instruments, yields modulus data that are in good agreement with conventional Instron tensile tests.

Financial Support:

• • Air Products and Chemicals

• • ATOFINA Chemicals, Inc.

Combinatorial Screening of Biocompatible Polymer Surfaces

Perhaps the most vital need for developing polymeric biomaterials is surfaces that actively control cellular and physiological responses. Such "bioactive" polymers could be used in tissue engineering scaffolds that support and regulate the adhesion, growth, and function of target cells.

 

We have developed a novel combinatorial methodology for characterizing the effects of polymer surface features on cell function. Libraries containing hundreds to thousands of distinct microstructures and roughnesses are prepared using composition spread and temperature gradient techniques (Figure 1).

The technique overcomes complex variable spaces that limit development of biomaterial surfaces for control of cell function by enabling:

• orders of magnitude increases in discovery rate

• decreased variance

• high-throughput assays of cell response to physical surface features.

In particular, we use the phenomenon of heat-induced phase separation in these polymer mixtures to generate libraries with diverse microstructure and roughness, followed by culture of cells such as osteoblasts (Figure 2), capillary endothelial, human hematopeoitic stem cells, and aortic smooth muscle cells on the libraries. With these high-throughput cell cultures, we discover novel regions of surface chemistry and roughness where cells adhere and function optimally (Figure 2).

Financial Support:

• • NIH - National Center for Research Resources

• • NIH - National Heart, Lung, and Blood Institute

• • Rockefeller Brothers Fund

• • Ga Tech - Emory Biomedical Engineering Seed Grant

Stabilization of Polymeric Semiconductor-Insulator Interfaces

The incorporation of polymeric semiconductors into logic devices, data storage, and sensors is a critical step for 'portable', 'durable' or 'expendable' micro- and nanoelectronics applications, e.g., real-time biosensors in food packaging or medical diagnostics or organic light-emitting diodes (OLEDs). As the need for more computing speed and storage grows, the scale of device structures will shrink into the nanoscale regime: less than 100 nm. A major roadblock to polymeric semiconductors is the inherent instability of nanoscale thin films and interfaces with dissimilar materials like insulators or strong conductors.Researchers at the Georgia Institute of Technology are working on a solution to this dilemma. J. Carson Meredith (Asst. Professor, Chemical and Biomolecular Engineering) and post-doc Santanu Chattopadhyay are applying combinatorial screening techniques to investigate and optimize the stability of semiconducting poly(3-octylthiophene) and its interfaces with simple insulators like poly(styrene). The high-throughput characterization of large numbers of thickness combinations is based upon the creation of thin-film libraries with two-dimensions of thickness variation, shown in Figure 1. A major discovery is that dramatic changes in wetting behavior occur over ranges of P3OT thickness in which molecular alignment is changing (Fig 2). Current theories of film instability do not capture this type of thickness dependent interfacial energy.

Financial Support:

• • ACS Petroleum Research Fund

• • NSF: Nanoscale Exploratory Research Grant

• 
  Molecular Thermodynamics of Nanoparticle-Polymer Systems
  Monte-Carlo Computer Simulation of Chemical Potentials

  Nanoscale colloidal particles, as well and inorganic phases synthesized in situ in organic materials, display fascinating electronic, optical, thermal, and reinforcement properties as a consequence of their dimensions. Stable dispersions of nanoscale colloids may find applications in drug delivery, medical diagnostics, nanopatterning and nanocomposites. The self-assembly of nanoparticles into ordered crystalline arrays offers an attractive route to fabrication of a new generation of optical and electronic devices.

  Unfortunately, robust molecular based models of these complex multiscale mixtures are still in their infancy and relationships between molecular parameters and nanoparticle phase behavior are determined often by trial-and-error experimentation. A major contribution to this complexity is the adsorption of surface modifiers and the subsequent change in their available conformations.

  Towards this goal, we recently developed a novel application of the expanded ensemble Monte Carlo (EEMC) simulation method that allows accurate calculation of the chemical potentials of organically-modified nanoparticles. Knowledge of the modifier chain length, concentration and particle size dependence of chemical potential can be used to predict conditions under which nanocolloids disperse, flocculate, or self-assemble. We are using the simulation technique to understand the structure and free energy of polymers around nanoparticles (Figure 1) and to probe the interparticle forces between nanoparticles immersed in polymer solutions (Figure 2).

  Financial Support:

  • • Ga Tech - IPST Seed Grant & Georgia Tech Start-Up Funds

  • • This work is supported by a grant from the National Science Foundation, CTS-0210479.

  • Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation

 

ChBE Central Office: 311 Ferst Drive, Atlanta, GA 30332-0100    |   Phone: (404) 894-1838   |    Fax: (404) 894-2866

ACCESSIBILITY  |   CONTACT US  |   LEGAL & PRIVACY INFORMATION  |   TECHNOLOGY

©2005 Georgia Institute of Technology   ::   Atlanta, Georgia 30332