| Ionic polymer transducers (IPTs) represent a relatively new class of active ('smart') materials, which can function as highly sensitive mechanical sensors as well as actuators. An IPT is made of an ionic polymer membrane sandwiched between two conductive electrodes. They generate controllable strain when applying a low voltage (<5 V) across their thickness and generate measurable currents due to extremely small mechanical strain. IPTs are cost effective and often have superior sensing capabilities compared to other active materials such as piezoelectrics. However, this novel class of transducers has not been widely employed mainly because the mechanism of IPT sensing is not clearly understood.In this dissertation, the mechanical properties of ionic polymers (Nafion and Selemion), the ionomer morphology, and the fundamental mechanism responsible for the electromechanical sensing responses of IPTs are studied. A multiscale model for the prediction of material stiffness is presented. The results give access to a fundamental material parameters currently inaccessible via experimentation, namely local stiffness. Subsequently the sensing mechanism of stream potential is hypothesized. It is argued that the mechanism of streaming potential, unlike prior hypotheses, is able to systematically explain generalized experimentally observed sensing phenomena, such as the observation of an optimum conductive particulate volume fraction in the interpenetrating electrode region of the transducer. Moreover, it is argued that coupling the exploration of local stiffness and streaming potential is prerequisite to gaining insight into subtler experimental sensing phenomena such as experimentally observed variations in sensing due to variations in IPT architecture. |
