(753d) AC Impedance Spectroscopy and Equivalent Circuit-Based Modeling As a Means to Probe the Micro and Nanostructure of Charged Colloidal Systems

Reducing costs and increasing power densities of fuel cell and battery technologies requires improved material utilization.  We are studying ionically conductive layered nanoclays (smectites and layered double hydroxides) as possible building blocks for fuel cell and battery structures.  The goal of this technique is to locate the ionic conductor in close-proximity to the fuel cell catalyst or battery electrode material by tailoring the structure at the nano-level.  Self-assembly characteristics of these charged, colloidal systems can then also be employed to produce structures with appropriate transport characteristics (ionic, electronic, and in the case of fuel cells, fuel and air).

The orientation, self-assembly, and aggregation characteristics of colloidal particles is often probed using rheological or light scattering techniques.  Standard rheological techniques do not generally afford a long time window for study on an individual sample if solvent evaporation is a concern.  Light scattering techniques (static and/or dynamic) allow for sealed samples to prevent solvent evaporation, but are often limited to dilute and/or transparent dispersions.  AC impedance measurements can provide a study of these properties while allowing for sealed samples for long periods of time as well as over a wide range of colloid concentrations.

We have been using AC impedance measurements to characterize the conductivity of our colloidal gels, and have begun to realize a side benefit of also providing insight into the colloidal micro and nanostructure as well, particularly when coupled with relatively simple equivalent circuit-based models.  This technique has been used to investigate the micro and nanostructure of nanclay-based gels, with varying clay cation-exchange capacity and primary particle size, as well as varying salt concentrations.  We have begun to study the impact of organic solvents and water soluble polymers and have been designing a modified system to provide insight into the self-assembly behavior of these materials.  The general technique will be presented, as well as past and current results.