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Ionic polymer transducers (IPTs) are soft sensors and actuators which operate through a coupling of micro-scale
chemical, electrical, and mechanical interactions. The use of an ionic liquid as solvent for an IPT has been
shown to dramatically increase transducer lifetime in free-air use, while also allowing for higher applied voltages
without electrolysis. In this work we model charge transport in an ionic liquid IPT by considering both the
cation and anion of the ionic liquid as mobile charge carriers, a phenomenon which is unique to ionic liquid
IPTs compared to their water-based counterparts. The electrochemical behavior of the large ionic liquid ions is
described through a modification of the Nernst-Planck equation given by Kornyshev which accounts for steric
effects in double layer packing. The method of matched asymptotic expansions is applied to solve the resulting
system of equations, and analytical expressions are derived for the nonlinear charge transferred and capacitance
of the IPT as a function of the applied voltage. The influence of the fraction of mobile ionic liquid ions and steric
effects on the capacitance of an ionic liquid IPT is shown and compared to water-based IPTs. These results show
the fundamental charge transport differences between water-based and ionic liquid IPTs and give considerations
for future transducer development.
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