A number of materials have been explored for their use as artificial muscles Among these, dielectric elastomers (DEs) appear to provide the best combination of properties for true muscle-like actuation DEs behave as compliant capacitors, expanding in area and shrinking in thickness when a voltage is applied Materials combining very high energy densities, strains, and efficiencies have been known for some time To date, however, the widespread adoption of DEs has been hindered by premature breakdown and the requirement for high voltages and bulky support frames Recent advances seem poised to remove these restrictions and allow for the production of highly reliable, high-performance transducers for artificial muscle applications

Advances in dielectric elastomers for actuators and artificial muscles.

The increasing understanding of the advantages offered by fish and insect-like locomotion is creating a demand for muscle-like materials capable of mimicking nature's mechanisms. Actuator materials that employ voltage, field, light, or temperature driven dimensional changes to produce forces and displacements are suggesting new approaches to propulsion and maneuverability. Fundamental properties of these new materials are presented, and examples of potential undersea applications are examined in order to assist those involved in device design and in actuator research to evaluate the current status and the developing potential of these artificial muscle technologies. Technologies described are based on newly explored materials developed over the past decade, and also on older materials whose properties are not widely known. The materials are dielectric elastomers, ferroelectric polymers, liquid crystal elastomers, thermal and ferroelectric shape memory alloys, ionic polymer/metal composites, conducting polymers, and carbon nanotubes. Relative merits and challenges associated with the artificial muscle technologies are elucidated in two case studies. A summary table provides a quick guide to all technologies that are discussed.

Artificial muscle technology: physical principles and naval prospects

This review collects recent developments in the field of liquid crystalline elastomers (LCEs) with an emphasis on their use for actuator and sensor applications. Several synthetic pathways leading to crosslinked liquid crystalline polymers are discussed and how these materials can be oriented into liquid crystalline monodomains are described. By comparing the actuating properties of different systems, general structure-property relationships for LCEs are obtained. In the final section, how these materials can be turned into usable devices using different interdisciplinary techniques are described.

Liquid Crystalline Elastomers as Actuators and Sensors

Energy harvesting exploits ambient sources of energy such as mechanical loads, vibrations, human motion, waste heat, light or chemical sources and converts them into useful electrical energy. The applications for energy harvesting include low power electronics or wireless sensing at relatively lower power levels (nW to mW) with an aim to reduce a reliance on batteries or electrical power via cables and realise fully autonomous and self-powered systems. This review focuses on flexible energy harvesting system based on polyvinylidene fluoride based polymers, with an emphasis on manipulating and optimising the properties and performance of the polymeric materials and related nanocomposites through structuring the material at multiple scales. Ferroelectric properties are described and the potential of using the polarisation of the materials for vibration and thermal harvesting using piezo- and pyro-electric effects are explained. Approaches to tailor the ferroelectric, piezoelectric and pyroelectric properties of polymer materials are explored in detail; these include the influence of polymer processing conditions, heat treatment, nanoconfinement, blending, forming nanocomposites and electrospinning. Finally, examples of flexible harvesting devices that utilise the optimised ferroelectric polymer or nanocomposite systems are described and potential applications and future directions of research explored.

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Multiscale-structuring of polyvinylidene fluoride for energy harvesting: the impact of molecular-, micro- and macro-structure

The complexity of materials aging may be seen as a result of the interplay between several activation processes operating on multiple spatial and temporal scales. Though the disciplines involved may seem disparate at first, material aging fundamentally could be linked by the same set of underlying activations and responses of the system. We examine how recent studies of shear-induced deformation and rheological flow initiated in the soft-matter community can be leveraged to probe the mechanisms of radiation damage in nuclear materials. Bridging these two traditionally separate areas of research demonstrates the emerging notions of mesoscale science as a research frontier concerned with linking macroscale behavior to microscale processes in driven systems. We suggest the combining of microstructuresensitive measurements with fundamental theories and mechanism-specific simulations is essential to addressing metastable materials responses of strongly activated states.

Current Opinion in Solid State and Materials Science

Microtomized sections of single-crystalline ferroelectric liquid crystalline elastomers (SC-FLCE) have been prepared. The piezoelectric (and electrostrictive) responses in these sections have been measured by means of an interferometric setup and the pyroeletric properties have been determined using the laser intensity modulation method (LIMM).

Piezoelectric and Pyroelectric Investigations on Microtomized Sections of Single-Crystalline Ferroelectric Liquid Crystalline Elastomers (SC-FLCE)

The pyroelectric response and the thermal properties of microtomized sections of 'single-crystalline' ferroelectric liquid crystalline elastomers (FLCE) have been investigated. The microtomized sections were manufactured in the thickness range from 20 to 100 mum. The roughness of the surfaces due to the cutting process was investigated with an alpha-stepper and found to be in the range of about 5 mum. The thermal diffusivity of the elastomer at different temperatures was determined by placing the sample on a pyroelectric substrate and measuring the pyroelectric signal of the substrate under appropriate conditions. From the pyroelectric current spectra, information about the spatial distribution of the polarization could be deduced. It was found to be constant except in a range also about 5 mum near the surface. From the combination of this result and that of the alpha-stepper measurements, the conclusion is drawn that the molecular orientation at the surface is destroyed due to the cutting process. The ma...

Measurement of the pyroelectric response and of the thermal diffusivity of microtomized sections of 'single crystalline' ferroelectric liquid crystalline elastomers

Spatially resolved polarization and charge distributions have been investigated in sandwich cells of two ferroelectric liquid crystal side-chain polymers and a low molecular weight ferroelectric mixture. For measurements without external field, contributions to the distribution at the surface of the liquid crystal layer have been found for all three materials. These are attributed to nonvanishing polarization due to surface interaction of the molecules. For both polymeric materials there is a strong dependence of the shape of the measured pyrospectra on the sample temperature. This is attributed to changes in material parameters. In contrast to this, for the low molecular weight substance only minor changes are visible.



For an applied external electric field, additional contributions to the resulting distribution caused by charge layers and by polarization due to helix unwinding can be observed. Charge layers are located near the surface of the liquid crystal layer. Helix unwinding can be observed for the low molecular weight material at room temperature. One of the polymers which is in the glassy state at room temperature shows corresponding effects above its glass transition point. © 1998 John Wiley & Sons, Ltd.

Investigations on ferroelectric liquid crystalline systems with the laser intensity modulation method

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Piezoelectric and Pyroelectric Investigations on Microtomized Sections of Single-Crystalline Ferroelectric Liquid Crystalline Elastomers (SC-FLCE)

Measurement of the pyroelectric response and of the thermal diffusivity of microtomized sections of 'single crystalline' ferroelectric liquid crystalline elastomers

Investigations on ferroelectric liquid crystalline systems with the laser intensity modulation method