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Ionic polymer transducers (IPT), sometimes referred to as artificial muscles, are known to generate a large bending strain
and a moderate stress at low applied voltages (<5V). Recently Akle and Leo[1] reported extensional actuation in ionic
polymer transducers. In this study, extensional IPTs are characterized under forced and free displacement boundary
condition as a function of transducer architecture. The electrode thickness is varied from 10 μm up to 40 μm while three
extensional actuators with Lithium, Cesium, and tetraethylammonium (TEA) mobile cations are characterized. Three
fixtures are built in order to characterize the extensional actuation response. The first fixture measures the free
displacement of an IPT sample sandwiched between two aluminum plates glued using the electrically conductive silver
paste. In the second fixture a spring is compressed against the test sample with variable amounts to generate different
levels of pre-stress and prevents the bending of the IPT. In the third fixture dead weights are placed on top of the sample
in order to prevent bending. In the spring loaded fixture a thermocouple is placed in the proximity of the actuator and
temperature is measured. The different transducers are characterized using a step voltage input and an alternating
current (AC) sine wave input. The step input resulted in a logarithmic rise like displacement curve, while the low
frequency (<0.1 Hz) AC excitation generated a sine wave displacement response with a strong first harmonic. The high
frequency AC excitation generated a response similar to that of the step input. Comparing the measured temperature for
step and AC response demonstrated that the sample is heating up when exited with a high frequency signal; which is
leading to the expansion of the sample. Initial experimental results demonstrate a strong correlation between electrode
architecture and the peak strain response. Strains on the order of 2% are observed with air stable ionic liquid based
transducers. A correlation between the strain and charge buildup in the polymer is also characterized. Cesium (Cs)
mobile cation outperformed all other tested mobile charges, while Potassium displaced the least.
Keywords: Ionic Polymers, Transducer, Actuator, Electroactive Polymer, Extensional Actuator.
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