Electrochemical switching of conducting polymers: A variable resistance transmission line model

Numerical Modeling of an Organic Electrochemical Transistor

We develop a numerical model for the current-voltage characteristics of organic electrochemical transistors (OECTs) based on steady-state Poisson’s, Nernst’s and Nernst–Planck’s equations. The model starts with the doping–dedoping process depicted as a moving front, when the process at the electrolyte–polymer interface and gradually moves across the film. When the polymer reaches its final state, the electrical potential and charge density profiles largely depend on the way the cations behave during the process. One case is when cations are trapped at the polymer site where dedoping occurs. In this case, the moving front stops at a point that depends on the applied voltage; the higher the voltage, the closer the stopping point to the source electrode. Alternatively, when the cations are assumed to move freely in the polymer, the moving front eventually reaches the source electrode in all cases. In this second case, cations tend to accumulate near the source electrode, and most of the polymer is uniformly doped. The variation of the conductivity of the polymer film is then calculated by integrating the density of holes all over the film. Output and transfer curves of the OECT are obtained by integrating the gate voltage-dependent conductivity from source to drain.

Computational design of mixers and pumps for microfluidic systems, based on electrochemically-active conducting polymers

We present a theoretical description of the propagation of composition waves along a strip of electrochemically-active conducting polymer, upon electrochemical stimulation. We develop an efficient solution of the electro-neutral Nernst-Plank equations in 2-D for electromigration and diffusional transport in the solution based on an extension of the methods of Scharfetter and Gummel [D. L. Scharfetter and H. K. Gummel, IEEE Trans. Electron Devices, 1969, ED16, 64-77.] and of Cohen and Cooley [H. Cohen and J. W. Cooley, Biophys. J., 1965, 5, 145-162.], and demonstrate important effects of the geometry of the cell. Under some circumstances, waves reflecting back from the end of the strip are predicted. We then demonstrate theoretically how such waves, associated as they are with expansion of the polymer, could be employed to enhance mixing or induce pumping in microfluidic systems.

Active control of epithelial cell-density gradients grown along the channel of an organic electrochemical transistor

Complex patterning of the extracellular matrix, cells, and tissues under in situ electronic control is the aim of the technique presented here. The distribution of epithelial cells along the channel of an organic electrochemical transistor is shown to be actively controlled by the gate and drain voltages, as electrochemical gradients are formed along the transistor channel when the device is biased..