Electrochemically driven polypyrrole bilayers for moving andpositioning bulk micromachined silicon plates

The conjugated polymer polypyrrole undergoes a volume change of several percent when its oxidation state is changed electrochemically by the application of voltages between 0 and -1 V (versus Ag/AgCl). This volume change is due to ion movements in or out of the polymer film. Bilayers of polypyrrole and gold undergo a large bending and can deliver high force. They can thus function as hinges to lift rigid components. In this work, we demonstrate that silicon plates produced by reactive ion etching can be lifted by such PPy/Au hinges. The strength and efficiency of these bilayers are also determined     

Edge effects determine the direction of bilayer bending

We elucidate the reason for preferential bending along the long edge in thin rectangular bilayers in which one of the layers is isotropically strained. While this preference has been observed previously, the physical basis for this preference has not been understood. We find that the bending direction is determined by the existence of doubly curved regions at the curled edges, which lower the energy. This energy difference between "spiral" and "cigar" shapes increases with aspect ratio.     

Elastomers filled with exfoliated graphite as compliant electrodes

A compliant electrode material has been realized by blending an insulating polydimethylsiloxane (PDMS) elastomer with a conductive exfoliated graphite filler, which was produced by microwave irradiation. The conductivity and stiffness of the electrodes were determined as a function of filler concentration. These materials exhibited a low percolation threshold: above 3 wt.% loading they became conductive, with conductivities reaching as high as 0.4 S/cm. They remained elastomeric upon loading up to 25 wt.%, having a Young’s modulus of only 1.4 MPa. This modulus (corresponding to a 220% increase compared to the unloaded PDMS) is the lowest reported for loaded elastomers above the percolation threshold. Scanning electron microscopy showed that the composites contained small voids, unlike unloaded PDMS, which might be responsible for the low modulus. The performance of these electrodes is comparable to that of PDMS loaded with carbon nanotubes, but the exfoliated graphite material can be produced at a fraction of the cost.     

Conjugated Polymer Actuators for Biomedical Applications

Conjugated polymers are electroactive and have found applications as artificial muscles. Actuators that have been developed over the last decade have now reached the early stages of commercialization, particularly for use in biomedical devices. This article reviews the motivation for using this class of actuator, the types of devices that have been fabricated, and some of the biomedical applications that are being developed. Recommendations are presented for future work on understanding the actuation mechanisms, on actuator design, and on the measurement of metrics.