Sensors and Actuators B 151 (2010) 198–204 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Electric-stimuli-responsive bending actuator based on sulfonated polyetherimide Mahendran Rajagopalan, Jin-Han Jeon, Il-Kwon Oh ∗ Division of Ocean Systems Engineering, School of Mechanical, Aerospace and Systems Engineering, Korea Advanced Institute of Science and Technology, 335 Gwahak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea article info Article history: Received 25 April 2010 Received in revised form 8 September 2010 Accepted 9 September 2010 Available online 18 September 2010 Keywords: Electromechanical actuators Polyetherimide Functionalization of polymers Proton conductivity Scanning electron microscopy abstract In this study, based on the ionic exchangeable membrane of biocompatible sulfonated polyetherimide (SPEI), a novel electric-stimulus-responsive bending actuator was developed. The degree of sulfonation of SPEI was controlled with chlorosulfonic acid and was analyzed by using 1 H nuclear magnetic resonance spectroscopy and thermogravimetric analysis. The SPEI membrane prepared by a solution casting method shows good electro-chemical properties of ion-exchange capacity, water uptake and proton conductivity required for a high-performance ionic polymer actuator. The SPEI ionic polymer–metal composite actu- ator, which was prepared by coating platinum layers on both sides of the membrane by an electroless plating process, shows good harmonic and step responses as an electro-active polymer. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Electroactive polymers (EAPs) can convert electrical energy to mechanical energy, and are potential candidates for artificial mus- cle actuators [1], active catheters [2] and biomimetic robots [3,4]. EAPs, such as ionic-polymer metal composites (IPMCs) [5,6], ionic polymer gels [7], conductive polymers [8], carbon nanotube actua- tors [9], dielectric elastomers [10] and cellulose actuators [11] are commonly employed in making artificial muscles. The IPMC [5] is a new class of biomimetic actuators, whose electromechanical per- formance is similar to that of natural muscles. In the IPMCs, the mobility of ions, protons and water molecules inside the mem- brane are strongly involved in the actuation mechanism [12] under electrical fields. IPMCs are prepared by plating electrode layers on the surface of an ionic exchangeable membrane like Nafion and Flemion. The IPMC shows transverse bending deformation, when electrical fields are applied across the surfaces of the polymer elec- trolyte membrane. The IPMC has several advantages such as light weight, physical flexibility, quick actuation, and large bending dis- placement at low voltages. Nafion perfluorosulfonic polymer was generally used for the IPMC actuators, because of its light weight, large bending deforma- tion, and low power consumption [13]. However, they have certain drawbacks such as low actuation bandwidth, low blocking force, high cost and a hazardous fluorinated polymer. To overcome these ∗ Corresponding author. Tel.: +82 42 350 1520; fax: +82 42 350 1510. E-mail address: ikoh@kaist.ac.kr (I.-K. Oh). drawbacks, functionalized ionic polymers are being considered as candidates for the novel IPMC actuators. Sulfonated polymers are commonly used in the IPMC actuators [14–18], because of their high hydrophilic nature, water uptake, and high proton conductivity. Polyetherimide (PEI) is an amorphous polymer that has excel- lent mechanical and chemical stability, solvent resistance, high heat resistance and good film-forming properties [19]. It has repeated phenyl groups, imide groups, ether linkages and angular bonds between aromatic rings [19,20]. Compared to conventional Nafion membranes, the biocompatibility of PEI membranes was validated for potential use as a biomaterial [21–24]. Also, the PEI membrane has important advantages of cost effectiveness and stiffness con- trollability required to be used for polymer actuators. The cost of polyetherimide (255.4 US $/kg) is much cheaper than Nafion 117 solution (363.7 US $/100 ml). However, until now the PEI mem- brane was not used to make a cost-effective ionic polymer actuator with electric-stimuli-responses, focusing on the biomedical appli- cations. In this study, an electro-active polymer based on a sulfonated polyetherimide (SPEI) that has good biocompatibility was first developed for future biomedical active devices such as active catheters and stents. To improve the performance of PEI for use in actuators, the sulfonic acid group is introduced into the polymer backbone to increase its physicochemical properties such as proton conductivity, water uptake, and hydrophilic nature. Mechanical, electrical, and thermal properties and the water uptake of the SPEI membrane were also studied. Through electroless plating and ion- exchange processes, the electro-active SPEI actuator was finally obtained and the electromechanical bending deformations and 0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.09.021