Effect of Sulfur-Containing Dopants on Filling Efficiency for Conducting Polymers

Abstract

Cellular physiology is sensitive to minute changes in the chemical composition of its environment. Therefore, understanding the effect of ionic concentration is significant to understanding healthcare (diagnosis and treatment). Electrically conductive polymers, such as polypyrrole, exchange ions with solution by the application of electrical potentials and thus alter the chemical composition of the solution without the use of microfluidics. Calculation of morphology-dependent parameters, such as filling efficiency, assists in quantifying these transport phenomena. In an effort to understand how conducting polymers may influence cellular physiology, a conducting polymer's cation storage capacity was measured to calculate the ability of the conducting polymer to change the chemical makeup of an ionic solution. Polypyrrole samples were fabricated using three dopants (p-toluene sulfonate, dodecyl sulfate, and dodecylbenzenesulfonate) at charge densities of 0.4 C/cm2, 0.8 C/cm2, and 1.2 C/cm2. These membranes were pretreated with cyclic voltammetry until all ion exchange was reversible and then characterized by chronoamperometry. All tests were conducted with 100mM potassium chloride solution. The number of ions exchanged by polypyrrole with the solution was calculated by fitting the data to an exponential function used to describe ion transport and compared to the theoretical maximum ion storage of the polypyrrole film. Preliminary findings indicated that filling efficiency (ionic ingress divided by the theoretic maximum) was approximately equal across all dopants. As all three dopants possess a similar morphology, they form polymers with a comparable number of redox sites, and filling efficiency is largely dependent on the number of available redox sites. These findings establish that the filling efficiency of polypyrrole is independent of the dopant for a given dopant morphology.