Electrokinetic characterization of Zeonor and Nafion Surfaces: Onsager kinetic matrices for polymer-water systems
Brian Kirby (Cornell University)
Electrohydrodynamics and electrokinetics of fluid systems
Mon 10:45 - 12:15
Barus-Holley 161
We derive coefficients of the Onsager kinetic matrix for a system with porous and charged interfaces grafted onto a solid surface having a known potential, and demonstrate Onsager reciprocity for the cross terms. Our results link known and estimative physical and chemical properties of the solid-fluid system to flux densities of current and flow. Our expressions for the electrokinetic coupling coefficients are in terms of the potential and fixed charge only, removing dependences on field gradients and fluid velocity. Additionally, we present simplified expressions of these coupling coefficients in limiting regions of the parameter space. Away from these limits, we convey numerical results demonstrating the facility of our functional form for facile numerical approximation, as well as the utility and accuracy of our analytical approximations. Experimentally, we present results for electrokinetic characterization of Zeonor and Nafion films and interpret these results in the context of the onsager kinetic matrix. Both materials generate long transients (as long as days), for completely different reasons. Zeonor thin films lead to decaying electrokinetic response attributed to transient surface nanobubbles introduced following surface wetting; the decaying electrokinetic enhancement is a function of dissolved gases, electric fields applied, and solvent exchanges. Nafion thin films lead to decaying electrokinetic response attributed to oligomeric leaching and polymeric restructuring. The electrokinetic observations are supported by XPS, contact angle, AFM, and charge titration experiments.