Original Article Journal of Intelligent Material Systems and Structures 1–14 Ó The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1045389X15581520 jim.sagepub.com In situ scanning electron microscopy study of strains of ionic electroactive polymer actuators Andres Punning, Veiko Vunder, Indrek Must, Urmas Johanson, Gholamreza Anbarjafari and Alvo Aabloo Abstract We have developed a technique to determine the bending strain of ionic electroactive polymer actuators without the use of the macroscopic bending geometry. In situ comparisons of the scanning electron microscope micrographs from a bending ionic electroactive polymer actuator, using a digital image correction methodology, identify its bi-directional deformation field. The developed technique allows verification of the factual axial and thickness strains of any notional layer of the actuator, including the outer surfaces of the electrodes. Thus, calculation of the bending and thickness strains of the ionic electroactive polymer laminate becomes possible. Moreover, the technique allows the determination of the position of the neutral layerof bending that is an important requirement for the calculation of the second area and bend- ing moments of the beam. The four examples presented demonstrate the potential variations of the bending schemes, in cases where the neutral layer is at the centroid and shifted away from the centroid. Keywords Ionic electroactive polymer, actuator, digital image correlation, scanning electron microscope, neutral layer Introduction Ionic electroactive polymers (IEAP) are composite polymeric laminate materials that exhibit changes in their spatial extent when stimulated electrically. Even though the term ‘IEAP’ emphasises the word ‘polymer’, the composite is not necessarily consisted of only poly- meric materials. All IEAPs consist of a polymeric mem- brane and deformable electronically conducting electrodes. Depending on the particular IEAP type, the compliant electrodes are made of metal (Shahinpoor and Kim, 2001), some allotropes of carbon (Kosidlo et al., 2013), naturally conducting polymers (Temmer et al., 2013) or even from some conducting chemical compounds, such as RuO 2 (Akle et al., 2006). The third relevant component of the IEAPs is the liquid electro- lyte, consisted of cations and anions. Although some aspects of the mechanism are still under dispute, the volumetric changes of the IEAP materials are caused by the physical displacement of ions between the separate regions of the composite. Depending on the electrode material, two essentially different operating principles lead to similar bending or buckling behaviours of the membrane. When the elec- trodes are just electronically conductive, the cations and anions migrate in the presence of the applied electric field, causing imbalanced internal pressures near the opposite electrodes (Bhandari et al., 2012; Jo et al., 2013). In the case of the conducting polymer elec- trodes, the strain difference, responsible for bending, is generated by reversible electrochemical reactions within the opposite conducting polymer layers (Temmer et al., 2013). The resulting bending behaviours, caused by the two different processes, are so similar that they cannot be distinguished by a cursory examination. Commonly, the IEAP actuators are used in a canti- lever configuration, where the width of the actuator is up to a few dozen times larger than its thickness, and the length is several times larger than its width. When voltage is applied between the opposite faces of such a trilayer strip, the different expansion or contraction patterns of the two electrodes produces a large and eas- ily perceived bending of the ribbon. Even though the bending of the IEAP actuator is effective and visible, Intelligent Materials and Systems Laboratory, Institute of Technology, University of Tartu, Tartu, Estonia Corresponding author: Andres Punning, Intelligent Materials and Systems Laboratory, Institute of Technology, University of Tartu, Nooruse 1, Tartu 50411, Estonia. Email: andres.punning@ut.ee at Tartu University Library on June 14, 2015 jim.sagepub.com Downloaded from