Bending actuators based on ionic electroactive polymers

Official URL: http://risc01.sabanciuniv.edu/record=b1737579 (Table of Contents)

In this thesis, two actuation systems based on two different conductive polymers were designed, prepared and characterized. In the first part, polyaniline nanofibers were used as main actuation component. Polyaniline nanofibers have shown promising electrical and electrochemical properties which make them prominent candidates in the development of smart systems employing sensors and actuators. Their electrochemical actuation potential is demonstrated in this study. A trilayer composite actuator based on polyaniline nanofibers was designed and fabricated. Cross-linked polyvinyl alcohol was sandwiched between two polyaniline nanofibrous electrodes as ion-containing electrolyte gel. First, electrochemical behavior of a single electrode was studied, showing reversible redox peak pairs in 1 M HCl using a cyclic voltammetry technique. High aspect ratio polyaniline nanofibers create a porous network which facilitates ion diffusion and thus accelerates redox reactions. Bending displacement of the prepared trilayer actuator was then tested and reported under an AC potential stimulation as low as 0.5 V in a variety of frequencies from 50 to 1000 mHz, both inside 1 M HCl solution and in the air. The decay of performance of the composite actuator in the air is investigated and it is reported that tip displacement in a solution was stable and repeatable for 1000 s in all selected frequencies. In the second part of the thesis, a high performance ionic polymer-metal composite actuator (IPMC) based on proton conductivity of poly(styrene sulfonic acid) was fabricated using a simple and novel method. Poly(styrene sulfonic acid) (PSSA) as a well-known hydrophilic proton conductive functional group was radiation grafted on polyvinylidene fluoride (PVDF) at different graft levels. The material system is well known for the proton exchange membranes of fuel cells, however, its IPMC application is novel. Flexible, soft and porous membranes were prepared by simple solution casting technique. Physical, mechanical, thermal and actuation properties of prepared membranes were characterized and compared with Nafion®. The membrane with highest graft level showed comparable ion exchange capacity and proton conductivity with that of Nafion whereas its water uptake is near three-fold greater than Nafion. To make PVDF-g-PSSA based IPMC actuators, Pt particles were deposited on both sides of the membranes using electroless plating method. Actuation performance of the IPMC actuators under various AC potentials and different frequencies were investigated. The results revealed that the PVDF-g-PSSA membrane with highest graft level showed highest average bending strain at 0.1 Hz and 4 V. The enhanced bending actuation behavior was attributed to porous morphology and large water uptake of graft polymerized actuators. Compared with traditional Nafion-based IPMC, our bending actuator is cheaper, and its preparation is fast and simple. So, it can be a viable replacement candidate for the traditional Nafion in soft actuator systems.