Papers by Author: Tissaphern Mirfakhrai

Abstract: Conducting polymer actuators are of interest in applications where low voltage and high work density are beneficial. These actuators are not particularly fast however, with time constants normally being greater than 1 second. Strain in these actuators is proportional to charge, with the rate of charging being found to limit the speed of actuation. This rate of charging is in turn limited by a number of factors, the dominant factor depending on the actuator and cell geometry, the potential range, the composition and the timescale of interest. Mechanisms that slow response can be as simple as the RC charging time arising from the actuator capacitance and the series resistances of the electrolyte and the contacts, or may involve polymer electronic or ionic conductivities, which can in turn be functions of potential. Diffusion can also be a factor. An approach is presented to help estimate the relative magnitudes of these rate limiting factors, thereby enabling actuator designs to evaluated and optimized for a given application. The general approach discussed is also useful for analyzing rate limits in carbon nanotube actuators and other related technologies.

Abstract: Carbon nanotubes have attracted extensive attention in the past few years because of their appealing mechanical and electronic properties. Yarns made through spinning multiwall carbon nanotubes (MWNTs) have been reported. Here we study the application of these yarns as electrochemical actuators, and as force sensors. MWNT yarns are mechanically strong with tensile strengths reaching one GPa. When charge is stored in the yarns they change in length. This is thought to be because of a combination of electrostatic and quantum chemical effects. We report strains up to 0.6 %. The charged yarns can also generate current and change in voltage in response to a change in the applied tension. Electrostatic and quantum effects contributing to actuation are introduced along with the effect of the yarn geometry on actuation and other contributing factors.