Wednesday, 13 October 2004 - 9:40 AM

This presentation is part of : Mechanics and Thermodynamics of Polymers

Thermodynamics of Ion-carrying Polymers: Nano-scale Modeling and Macro-scale Experiments

Sia Nemat-Nasser, UC San Diego, UC San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0416

Ionic polymer-metal composites (IPMCs) are soft actuators and sensors. They consist of a thin polyelectrolyte membrane, plated on both faces by a noble metal, and is neutralized with the necessary amount of counter-ions, balancing the charge of anions covalently fixed to the backbone membrane. The anions in Aciplex and Nafion are sulfonates, whereas those in Flemion are carboxylates. Figure 1 shows the chemical composition of Nafion and Flemion. When a thin strip of an IPMC membrane in the hydrated state is stimulated by the application of a small (1 to 3 V) alternating potential, it undergoes a bending vibration at the frequency of the applied voltage, generally no more than a few tens of Hertz. A dry sample of a bare polymer or an IPMC in an aqueous environment absorbs water until the resulting pressure within its clusters is balanced by the elastic stresses that are consequently developed within its backbone polymer membrane. From this observation the stiffness of the membrane can be calculated as a function of the water uptake for various cations. I first consider the balance of the cluster pressure and the elastic stresses for the bare polymer (no metal plating) and then use the results to calculate the stiffness of the corresponding IPMC by including the effect of the added metal electrodes. The procedure also provides a way of estimating many of the microstructural parameters that are needed for the modeling of the actuation of the IPMCs.

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