Nanoscale electrostatic actuators in liquid electrolytes: analysis and experiment

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Title: Nanoscale electrostatic actuators in liquid electrolytes: analysis and experiment
Author: Kim, Doyoung
Abstract: The objective of this dissertation is to analytically model a parallel plate electrostatic actuator operating in a liquid electrolyte and experimentally verify the analysis . The model assumes the system remains in thermodynamic equilibrium during actuation , which enables the ion mass balance equations and Guass ? ? Law to be combined into the Poisson -Boltzmann equation . The governing equations also include the linear momentum equation including the following forces : the electric force , the osmotic force , the spring force , the viscous damping force , and the van der Waals force . Equations are also derived for the energy stored in the actuator . The analytical results emphasize the stored energy at mechanical equilibrium and the voltage versus electrode separation behavior including the instability . The analytical results predict that the system may not be a good actuator because the displacement has a very limited stable range , although the actuator would be suitable for bistable applications . The experiment consisted of a fixed flat gold electrode and a movable gold electrode consisting of a gold sphere several micrometers in diameter mounted on the end of an Atomic Force Microscope (AFM ) cantilever , which serves as the spring . The electrodes were separated by approximately 100nm of 1mM NaCl aqueous solution . The analytical results were not verified by the experiment . Relative to the analysis , the experiments did not show distinct critical points , and the experiments showed less electrode separation for a given applied electric potential . The experiments did show points at which the electrode separation versus electric potential rapidly changed slope , which may be instability points . It is suggested that this phenomenon may be due to coalesced gas bubbles on hydrophobic regions of the electrode surfaces , which are not included in the model . Although clean gold surfaces are hydrophilic , gold surfaces may become hydrophobic due to impurities .
URI: http : / /hdl .handle .net /1969 .1 /3079
Date: 2006-04-12

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Nanoscale electrostatic actuators in liquid electrolytes: analysis and experiment. Available electronically from http : / /hdl .handle .net /1969 .1 /3079 .

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