Sensors and Actuators B 147 (2010) 170–179 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb O 2 plasma treatment for ionic polymer metal nano composite (IPMNC) actuator Saim Saher, Sungwon Moon, Seong Jun Kim, H. Jin Kim ∗ , Yong Hyup Kim School of Mechanical and Aerospace Engineering and the Institute of Advanced Aerospace Technology, Seoul National University, Seoul 151-742, Republic of Korea article info Article history: Received 1 November 2009 Received in revised form 11 February 2010 Accepted 11 March 2010 Available online 18 March 2010 Keywords: O2 plasma Ionic polymer metal composite (IPMC) Nano particles Actuator abstract Ionic polymer membrane is successfully treated with O 2 plasma, by which needle-like structures from 1.5 m to 3 m in height are created on the membrane surface. Subsequently, a thin platinum electrode layer is deposited on the membrane surface by electroless chemical metal plating. By these processes, spherical nano platinum particles of about 80 nm in diameter are dispersed uniformly in a localized manner near the electrode surface. The concentration of nano particles is significantly increased with the repetition of the electroless chemical metal plating process. Our results indicate that this type of morphology reduces the surface resistance of IPMNC electrodes and increases electrical capacitance. The localized concentration of nano particles and improved electrical properties of the electrode significantly enhances the actuation displacement, force, and operational life of plasma-treated IPMNC actuator when compared with conventional IPMNC prepared under similar conditions. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Ionic polymer metal nano composites are smart actuators that utilize an ion exchange membrane (IEM). IEMs are permeable to cations or anions because of the unique ionic nature of the fixed per- fluorinated polymer backbone. There are several commercial ion exchange material manufacturers, and the popular products that have been used as IPMC materials include Aciplex TM from Asahi Chemical, Nafion TM from DuPont, Neosepta TM from Tokuyama, and Flemion TM or Selemion TM from Asahi Glass. At present all these products perform fairly well when they are properly treated by the IPMNC chemical plating techniques. In this research nafion from DuPont is used and platinum is selected as electrode material due to its good conductivity, high corrosion resistance, and work den- sities. In nafion the top and bottom electrode surfaces are formed by exchanging H + ions with metal ions. The cross-section of IPMNC resembles a sandwich with elec- trode layers outside and a polymer matrix in the center [1]. Ionic polymer consists of a fixed network with negative charges, bal- anced by mobile cations. The polymer network consists of pockets of solvents and thin boundary layers are generated by the appli- cation of an electric field. A layer deficient in cation forms on the anode side, while a layer containing large number of cation forms on the cathode side. Due to the accumulation of cations on the cath- ode side, water molecules move to this side and cause hydrophilic expansion. The stress in the polymer matrix causes bending toward the anode [2,3]. With time, the back diffusion of water molecules ∗ Corresponding author. Tel.: +82 2 880 1552; fax: +82 2 887 2662. E-mail address: hjinkim@snu.ac.kr (H.J. Kim). causes a slow relaxation toward the cathode. The degree of actua- tion obtained is a function of various parameters such as polymer thickness, type of polymer, type of counter ion, amount of water, quality of metallization, and surface area of the polymer membrane [4,5]. When a voltage higher than the electrolysis voltage of water is applied, blistering and damage to the electrodes was observed, which degrades performance of the IPMNC [6]. There have been various efforts to improve the performance of the IPMNC actuators in terms of displacement, actuation force, or water containment. Initial compositing followed by a surface elec- troding process was adopted to effectively grow platinum on the top of initial platinum surface. This approach yields thick, dense electrodes, which reduce the surface resistivity and enhance the actuator displacement [7]. Sputtering of gold or silver nano par- ticles on the platinum electrode layer was performed to improve the surface conductivity [8]. It was reported that Cu–Pt electrodes decrease the electrode resistance compared with the situation where Cu is absent [9]. The argon plasma treatment was performed to improve the adhesion between the metal electrode and parylene coating layer by suppressing the water leakage [10]. The effects of oxygen plasma treatment were observed to improve the actuator deflection by 20% [11]. Incorporation of silicate nano particles to nafion, forming a nano composite, greatly alters the mechanical and electrical properties of the IPMNC polymer matrix. The result- ing IPMNC has higher current density when subjected to an electric field. The silicate composite exhibits larger actuation forces due to the increased cation content and better surface coverage of the platinum electrode [12]. Performance improvements in one aspect usually accompany degradation in other aspects. For instance, if the actuation force is enhanced then the displacement is decreased, or if the actua- 0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.03.038