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UBC Theses and Dissertations

High-speed conducting polymer actuators for thin, flexible vibrotactile displays : fabrication, electro-chemo-mechanical characterization, and feasibility Hik, Freya


Fast-acting, thin, flexible, bending-type actuators are an emerging technology for applications, such as in tactile feedback devices. Conducting polymer (CP) tri-layer actuators are a category of electroactive material that exhibit relatively high strain (>1 %), high work density, operate at low voltages (< 1 V), are thin (microns), and biocompatible. Strain is proportional to charge in the CP; therefore, the faster charge moves through of the system, the faster the tri-layer actuates. Our objective was to optimize the electrical, ionic, and material properties of PEDOT:PSS/PVDF/PEDOT:PSS actuators to increase charge storage and transfer capabilities. The goal was to increase the actuation speed of these devices, such that they achieved sufficient displacements and forces at physiologically relevant frequencies for vibrotactile feedback. We hypothesized that we could optimize the electro-chemo-mechanical properties of the PEDOT:PSS-based actuators using polar solvents and ionic liquid, to increase actuation speed. We soaked samples in methanol, methanol mixed with EMITFSI (50%v/v), ethylene glycol, ethylene glycol mixed with EMITFSI (50%v/v), or dimethyl sulfoxide. These treatments improved both electrical and ionic conductivity of PEDOT:PSS. Our results suggested that diffusion of ions through the CP layers was the largest source of impedance. Therefore, ionic resistance dictated the RC time constants. Treatment with polar solvent combined with ionic liquid resulted in the largest actuation speed, with a cut-off frequency of 4-Hz. We measured resonant frequency at ~300-Hz for a 5-mm long beam treated with MeOH and EMITFSI. We then investigated designs for vibrotactile displays. We applied a viscoelastic model to predict the skin deflection our actuators achieved. Results showed that force generation was the primary limiting factor. Free beam deflection exceeded the frequency-dependent minimum perception threshold by up to two orders of magnitude. However, this deflection decreased substantially when the actuators were mechanically impeded by the fingertip. The model predicted that our actuators just barely exceeded the absolute threshold of human perception on the hand. In future work we plan to further optimize the fabrication process and design of these conducting polymer tactors for applications such as in non-invasive biomedical, wearable, and communication devices.

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