Dissertation Defense: Kinetics of Ion Transport in Conducting Polymers
- Dr. Vishnu Baba Sundaresan, Chair (ME)
- Dr. Carlos Castro (ME)
- Dr. Jonathan Song (ME)
- Dr. Vishwanath Subramaniam (ME)
- Dr. Jose Otero (Neuroscience)
Conducting polymers (CPs) exhibit coupling in the electrochemical and mechanical domains; reversible ion exchange with an electrolyte under an applied electrical voltage causes volumetric changes in the polymer matrix. The goal of this dissertation is to develop precise quantification techniques to assess the kinetics of ion transport in CPs. These techniques are based on the mechanics of ion storage in polypyrrole doped with dodecylbenzene sulfonate (PPy(DBS)). In this work, it is postulated that CP response is dictated by the driving force for ion ingress and the accessible ion storage sites in the polymer. Two mechanistic models are founded on this premise. First, a mathematical constitutive model is derived from the first law of thermodynamics to describe the chemomechanically coupled, structure dependent, input-output relationship in PPy(DBS). The uniqueness of this model is that mechanical expansion of the polymer is predicted without the incorporation of empirical coefficients available in literature. Further, a kinetic model is proposed to describe the current and charge response of PPy(DBS) to a step voltage input. The transfer-function based approach used to validate this model offers advantages over traditional lumped parameter models by quantifying the effect of polymer mass and morphology on the magnitude and rate of ion ingress. These metrics are valuable control variables for tuning the performance of CP based sensors, actuators and energy storage devices. This research leads to the development of a calibrated PPy(DBS) sensor for the determination of bulk electrolyte concentration. Additionally, a miniaturized sensor incorporated at the tip of an ultramicroelectrode demonstrates near-field sensing capabilities. These electrodes are used in conjunction with scanning electrochemical microscopy (with shear force imaging) to develop a novel imaging technique with potential biological applications.