Electromechanically Active Polymers

Abstract

Polymer InternationalVolume 59, Issue 3 p. 277-278 EditorialFree Access Electromechanically Active Polymers Federico Carpi, Corresponding Author Federico Carpi f.carpi@centropiaggio.unipi.it Interdepartmental Research Centre ‘E. Piaggio’, University of Pisa, ItalyInterdepartmental Research Centre ‘E. Piaggio’, University of Pisa, Italy.Search for more papers by this author Federico Carpi, Corresponding Author Federico Carpi f.carpi@centropiaggio.unipi.it Interdepartmental Research Centre ‘E. Piaggio’, University of Pisa, ItalyInterdepartmental Research Centre ‘E. Piaggio’, University of Pisa, Italy.Search for more papers by this author First published: 01 March 2010 https://doi.org/10.1002/pi.2790Citations: 28AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Electromechanically Active Polymers (EAPs) form a broad family of ‘smart materials’ capable of transducing energy from the electrical to the mechanical form, and vice versa. As such, they are used for electromechanical actuation and mechanoelectrical sensing, as well as mechanical energy harvesting to generate electricity1-5. While EAPs are traditionally known as ElectroActive Polymers, this denomination does not capture the specificity of the family, consisting of the ability to undergo significant deformation and/or stress changes in response to suitable electrical stimuli. Accordingly, that term is not used here, to explicitly exclude any other type of electrically induced/regulated ‘activity’, wherein the mechanical form is not the ultimate (or the initial) stage of the energy transformation chain of interest (as in the case, for instance, of electrically semiconducting or conducting polymers for plastic electronics). Today, EAPs represent a well established and promising scientific field of research and development. EAP materials are commonly classified in two major families: ionic EAPs, activated by an electrically-induced transport of ions and/or solvent, and electronic EAPs, activated by electrostatic forces1-5. Ionic EAPs include polymer gels6, ionic polymer metal composites7 (including later evolutions to ionic polymer conductor composites, and the variant of interpenetrating polymer networks8), conjugated polymers9, and carbon nanotubes10. Electronic EAPs include piezoelectric polymers11, electrostrictive polymers12, dielectric elastomers13, liquid crystal elastomers14, along with what is proposed here as the latest entry, represented by carbon nanotube aerogels15. While each EAP category shows specific electromechanical properties, typically suitable for different needs and applications, general features include high mechanical compliance, low density, ease of processing, inherent responsiveness to electrical stimuli, as well as low cost. As a result, EAP transducers, in general, are flexible, light-weight, structurally-simple, versatile, scalable, and cheap; additionally, when used as actuators they have sizable electromechanical performance and integrated force/stroke feed-back, and are noiseless and heat-free [1–5]. Although several EAP materials and their properties have been known for many decades, they have found very limited applications. Such a trend has changed recently, as a result of an effective synergy of at least three main factors: key scientific breakthroughs being achieved in some of the existing EAP technologies; unprecedented electromechanical properties being discovered in materials previously developed for different purposes; and a higher concentration of efforts for real exploitation of EAP materials. As an outcome, after several years of basic research, today the EAP field is just starting to undergo transition from academia into commercialization, with significant investments from large companies. EAP actuators are being developed for applications that so far have been precluded to conventional actuation technologies (mainly electric/electromagnetic, hydraulic/pneumatic and thermo-chemical motors). Usage spans from the micro- to the macro- scale in different sectors, such as medical and haptic devices, consumer electronics, and automation and robotic systems. Reported examples include micro-pumps and micro-valves for micro-fluidic systems (e.g. for lab-on-a-chip devices)1, 5, controlled release of active compounds for medical therapeutic devices (e.g. insulin release in blood stream)1, 5, miniaturized surgical tools for medical interventional systems (e.g. steerable catheters)1, 5, miniaturized implantable actuators as components of artificial organs (e.g. mechanical stimulators of cardiac tissue)1, 5, 16, robotic systems (including medical and industrial robots)1, 4, 16-18, variable-stiffness devices (e.g. safe actuators for robots interacting with humans and vibration dampers for vehicles)18, active orthoses for rehabilitation systems (e.g. hand and limb orthoses)1, 5, 18, pumps and valves for macro-fluidic systems (e.g. for low-pressure hydraulics and pneumatics)1, 18, tunable lenses for adaptive optics (e.g. for camera phones)1 and tactile displays for haptic systems (e.g. refreshable displays for Braille readers or displays with tactile feedback for control panels of consumer electronics)1, 5, 18. While the EAP technologies hold the potential to be disruptive for these and many other kinds of products, developing them to such an extent that they might become ‘off-the-shelf’, with standard and reliable performance, still requires considerable research efforts today. These should be aimed at addressing a number of remaining scientific and technological issues. Among those deserving of priority, it is worth stressing the need to increase lifetime and response speed for ionic EAPs, and the necessary reduction of driving electric fields for electronic EAPs. In an effort to disseminate current advances on EAP science and technology, including new materials, models, devices and applications, this special issue of Polymer International collects together some twenty papers authored by renowned groups from research and industry in the field. The papers deal with a number of relevant topics inherent to ionic and electronic EAPs. While Rasmussen et al. report some considerations on contractile polymer gels, three papers are focused on ionic polymer metal composites (IPMC): Pugal et alreview IPMC mechano-electrical transduction, Kruusamäe et al. describe a self-sensing IPMC actuator with patterned surface electrodes and Wang et al. report the use of sulfonated poly(styrene-ran-ethylene) as ionic membranes. Variants of IPMC transducers are treated by two additional contributions: Vidal et al. describe how PEDOT containing semi-interpenetrating polymer networks represent a versatile concept to design optical and mechanical devices, while Liu et al. show the influence of imidazolium-based ionic liquids on the performance of ionic polymer conductor network composite actuators. With regards to conjugated polymers (CP), while Otero et al. present a study on the conformational energy of the chains of poly (3, 4- ethylenedioxithiophene) films used as actuators, and Valer et al. describe how polypyrrole free-standing electrodes sense temperature or current during reaction, applications of CP actuators are reported by three additional papers: Shoa et al. describe an analytical model of a CP driven catheter, Naka et al. present the operation of a micro pump driven by actuators made of polypyrrole, and McGovern et al. report the use of the same type of material to operate the tail-fin of a robotic fish. In the field of electronic EAPs, while Sawano et al. describe an actuator that uses shear piezoelectricity of a chiral polymer, the rest of contributions deal with dielectric elastomer (DE) actuators. In particular, two papers address fundamental aspects and modelling, as Liu et al. discuss the electromechanical stability of Mooney-Rivlin-type DEs with nonlinear variable dielectric constant and Zhu et al. model nonlinear oscillations of DE balloons. Three contributions are focused on DE materials: Interpenetrating polymer networks based on acrylic elastomers and plasticizers with improved operating temperature range are presented by Zhang et al., while Michel et al. report a performance comparison between silicone and acrylic elastomers and Gallone et al. discuss perspectives for new DEs with improved performance, comparing approaches based on composites and blends. New devices are presented by Carpi et al., who developed millimeter-scale bubble-like DE actuators, and Benslimane et al., who report performance and challenges of the first commercial linear extending actuators. Finally, Carpi et al. present real-time control of DE actuators via bioelectric and biomechanical signals. As a whole, this special issue reflects the heterogeneity of the EAP field: a great variety of materials, methods, devices, models and applications, characterised by peculiar achievements and challenges, and accompanied by a significant diversity of technological development, spanning from initial laboratory investigations to emerging industrial products. Certainly, the fast growing EAP field appears as one of the greatest opportunities for polymer science and technology to develop useful products with unprecedented functionalities. REFERENCES 1Brochu P and Pei Q, Macromol Rapid Comm 31: 10– 36 (2009). 2Mirfakhrai T, et al, Mater Today 10: 30– 38 (2007). 3Madden J, et al, IEEE J. Oceanic Eng 29: 706– 728 (2004). 4 Y Bar-Cohen (ed.), Electroactive polymer (EAP) actuators as artificial muscles. Reality, Potential, and Challenges, 2nd edition. SPIE, Bellingham,WA (2004). 5 F Carpi and E Smela (eds.), Biomedical applications of electroactive polymer actuators, Wiley, Chichester (2009). 6Tanaka T, et al, Sci 218: 467– 469 (1982). 7Asaka K, et al, Polym. J. 27: 436– 440 (1995). 8Vidal F, Plesse C, Teyssié D and Chevrot C, Synth Met 142: 287– 291 (2004). 9Baughman RH, Synth. Met. 78: 339– 353 (1996). 10Baughman RH, et al, Sci. 284: 1340– 1344 (1999). 11Nalwa HS, Ferroelectric Polymers, Marcel Dekker, New York (1995). 12Zhang QM, et al, Sci 280: 2101– 2103 (1998). 13Pelrine R, et al, Sci., 287: 836– 839 (2000). 14Lehmann W, et al, Nat. 410: 447– 450 (2001). 15Aliev A, et al, Sci. 323: 1575– 1578 (2009). 16Shahinpoor M, Kim KJ and Mojarrad M, Artificial muscles: applications of advanced polymeric nanocomposites, Taylor & Francis, London (2007). 17Kim KJ and Tadokoro S, Electroactive polymers for robotic applications: artificial muscles and sensors, Springer, New York (2007). 18 F Carpi, D De Rossi, R Kornbluh, R Pelrine and P Sommer-Larsen (eds.), Dielectric elastomers as electromechanical transducers, Elsevier, Amsterdam (2008). Citing Literature Volume59, Issue3Special Issue: Electromechanically Active PolymersMarch 2010Pages 277-278 ReferencesRelatedInformation