Influence of Additives on the Properties of Casting Nafion Membranes and SO-Based Ionic Polymer–Metal Composite Actuators Yanjie Wang, 1,2 Hualing Chen, 1,2 Yongquan Wang, 1 Bin Luo, 1 Longfei Chang, 1 Zicai Zhu, 1,2 Bo Li 1,2 1 School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an, People’s Republic of China 2 State Key Laboratory for Strength and Vibration of Mechanical Structure, Xi’an Jiaotong University, Xi’an, People’s Republic of China As a typical smart material, ionic polymer metal com- posite (IPMC) has a sandwich structure, which con- sists of a base membrane and two thin metallic electrodes on both sides of the base membrane. The properties of the base membrane, Nafion as the most used base material, strongly affect the performance of IPMC actuator. This paper reports the effects of differ- ent additives, such as ethylene glycol (EG), dimethyl sulfoxide (DMSO), N, N 0 -dimethyl formamide (DMF), and N-methyl formamide (NMF), on the performances of the casting membranes and SO-based IPMC actua- tors. Studies have shown that the microstructures of the casting membranes with EG and DMSO as addi- tives are more loose and amorphous, leading to higher water contents and thus higher conductivity than those with DMF, NMF, and Nafion 117. Among the casting membrane-based IPMC actuators, EG-based IPMC actuator has larger deformation and blocking force, higher strain energy density and conversion efficiency at 2 V DC voltage, whose electromechanical properties are most close to that based on Nafion 117. POLYM. ENG. SCI., 00:000–000, 2013. V C 2013 Society of Plastics Engineers INTRODUCTION Ionic polymer–metal composites (IPMCs), as one of electroactive polymers (EAPs), are very suitable for actuators and sensors because of their electromechanical and mechanoelectrical response to applied voltage and mechanical deformation, respectively [1, 2]. When applied as actuators, IPMCs have many particularly advantages, such as large deflection, low-activation voltage, high compliance, lightness, softness, and so on. Hence, they are considered as an attractive smart material and have a large quantity of potential applications in robotics, aerospace, biomedicine, and so on [3–9]. How- ever, there are still some defects, such as slow response, back relaxation and low-blocking force, which mainly limit the IPMC actuator as a practical actuator in variety of applications and need to be addressed urgently [10, 11]. Generally, a typical IPMC has a sandwich structure, which consists of a base membrane, usually Nafion TM membrane (by DuPont), and two thin metallic electrodes on both sides of the membrane. The membrane is made of perfluorinated ionomers, varying in the length of back- bones (I) and branches (II) and in the nature of the ionic side group, usually sulfonate anions (III), whose chemical formula is given in Fig. 1. A certain amount of cations (R1) inside the base membrane, which balance the elec- trical charge of the anions fixed on the backbone of the membrane, could provide actuating ability when the volt- age is on-load. This coupled electrical–chemical–mechan- ical properties of IPMCs highly depend on several factors, such as the microstructure of the ionomer back- bone, type of the cations, the morphology and conductiv- ity of the electrodes, and so on. One of the most important factors that seriously affects the blocking force of IPMCs is the base membrane, which provides the backbone and ion transport medium of IPMCs during actuation process. At present, most of the studies on IPMCs are limited to the base membrane of Nafion series, for example, N117, N1110, which have a relatively poor thickness range from 50 to 250 lm result- ing in low-blocking force. Apparently, to enhance block- ing force, the easiest and the best way is to increase the thickness of the base membrane. So far there are two ways to form thick base membrane, namely, hot pressing [13] and solution casting [14], developed by Lee and Kim, respectively. The former integrates multilayers of Correspondenc to: Yongquan Wang; e-mail: yqwang@mail.xjtu.edu.cn Contract grant sponsor: National Natural Science Foundation of China; contract grant number: 51290294; contract grant sponsor: Natural Sci- ence Basis Research Plan in Shaanxi Province of China; contract grant number: 2012JM7002. DOI 10.1002/pen.23634 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2013 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2013