Natural Science Foundation of Fujian Province of China [2011J05140]; Fundamental Research Funds for Central Universities of Xiamen University [2011121045]An ionic polymer metal composite (IPMC) is a kind of electro-active polymer. Due to the properties of low driving voltage, large deformation, flexibility and lightness, it is becoming one of the more popular from a diversity of smart materials. In this study, a novel structure of Nafion (R) film is proposed to improve the performance of an IPMC. IPMC samples with a gradient structure in thickness are fabricated and their performance is investigated to confirm the validity of the gradient structure. The deformation displacement and the blocking force are compared under AC and DC voltage by experiments. The results indicate that the structure of gradient in thickness would improve the performance both in deformation displacement and blocking force

Qiu, Xiaochun

Sun, Daoheng

Xu, Bing

Zhao, Yang

Zheng, Gaofeng

Zheng, Jianyi

Zhuang, Mingfeng

孙道恒

赵扬

郑建毅

郑高峰

Xiamen University Institutional Repository

This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 59.77.43.191This content was downloaded on 12/07/2015 at 08:43Please note that terms and conditions apply.Improving the performance of IPMCs with a gradient in thicknessView the table of contents for this issue, or go to the journal homepage for more2013 Smart Mater. Struct. 22 115035(http://iopscience.iop.org/0964-1726/22/11/115035)Home Search Collections Journals About Contact us My IOPscienceIOP PUBLISHING SMART MATERIALS AND STRUCTURESSmart Mater. Struct. 22 (2013) 115035 (6pp) doi:10.1088/0964-1726/22/11/115035Improving the performance of IPMCswith a gradient in thicknessYang Zhao, Bing Xu, Gaofeng Zheng, Jianyi Zheng, Xiaochun Qiu,Mingfeng Zhuang and Daoheng SunDepartment of Mechanical and Electrical Engineering, Xiamen University, Fujian,People’s Republic of ChinaE-mail: sundh@xmu.edu.cnReceived 21 June 2013, in final form 26 September 2013Published 24 October 2013Online at stacks.iop.org/SMS/22/115035AbstractAn ionic polymer metal composite (IPMC) is a kind of electro-active polymer. Due to theproperties of low driving voltage, large deformation, flexibility and lightness, it is becomingone of the more popular from a diversity of smart materials. In this study, a novel structure ofNafion R© film is proposed to improve the performance of an IPMC. IPMC samples with agradient structure in thickness are fabricated and their performance is investigated to confirmthe validity of the gradient structure. The deformation displacement and the blocking force arecompared under AC and DC voltage by experiments. The results indicate that the structure ofgradient in thickness would improve the performance both in deformation displacement andblocking force.(Some figures may appear in colour only in the online journal)1. IntroductionAn IPMC is a new kind of electro-active polymer which hasa ‘sandwich’ structure. It comprises three layers: one ionexchange film between two thin metal electrode layers. Theinherent property of an IPMC has many advantages, such asflexibility, lightness, chemical stability and fast response, etc.The most attractive property is the large bending deformationunder low driving voltage [1–3]. The bending deformationof an IPMC is generated by redistribution under electricalstimulation of its internal water molecules. When the electricfield is applied across the thickness of an IPMC, the hydratedcations with water molecules move together towards thecathode which results in swelling near the cathode side andcontraction near the anode side of the IPMC. The internalextensional stress of the polymer causes the IPMC to bendtowards the anode direction [4, 5]. An IPMC can also outputan electrical signal under the deformation of an externalforce, so it could be used as both actuator and sensor; thishas significant potential in a wide range of applications,including the field of biomimetics, robotics, medical devicesand aerospace. The major drawback which greatly limitsthe application of IPMCs is the low blocking force andresponse frequency. The challenge of IPMCs is mainly aboutaccurately controlling the interaction of mechanical, electricaland chemical properties in the ionic polymer [6–9].A great deal of research has been carried out intoimproving the performance, environment adaptability andapplicability of IPMCs. Several new fabrication methods havebeen developed, such as physical metal loading, hot-pressing,using new materials as electrodes, etc. Kim et al studiedthe performance of IPMCs with various thicknesses forextensive application [10]. Bennett et al used an ionic liquidto replace water as the solvent to improve the stability ofthe IPMC’s performance in air [11]. Lee et al proposedhot-pressing to fabricate thick IPMCs and performed severalcycles of Pt electroless plating to improve the actuatingperformance [12]. Fukushima et al developed a dry actuatorthat was fabricated by layer-by-layer casting of bucky gel.The advantage of the actuator is durability in air [13, 14].Akle et al proposed a new manufacturing technique of directassembly process to fabricate large strain ionic polymertransducers, in which the electrode material was sprayedonto ionic-liquid Nafion R© and hot-pressed [15–17]. Nguyenet al used Nafion R© layered silicate and Nafion R© silicananocomposites to fabricate IPMCs; the blocking forceis greatly improved with limited relaxation [18]. Plasmatreatment was introduced to roughen the Nafion R© surface in10964-1726/13/115035+06$33.00 c© 2013 IOP Publishing Ltd Printed in the UK & the USASmart Mater. Struct. 22 (2013) 115035 Y Zhao et alFigure 1. The casting procedure of gradient Nafion R© film.order to improve the actuation performance of IPMCs [19].Chung et al proposed micro-fabrication technologies byapplying silver nano-powders for the fabrication of IPMCsto improve the adhesion between electrodes and polymerwithout surface roughening pretreatment [20]. Mukai et alused millimetre long single walled carbon nanotubes to obtaina quick response and large bending actuator [21]. Palmreet al introduced carbon aerogel as a new material for thefabrication of nanoporous electrodes for EAP actuators usingthe direct assembly process [22]. Yip et al developed CNTionic polymer actuators and the performance can be tuned bythe addition of different CNT concentrations [23]. All thesestudies are aimed at improving the performance by usingnew materials in the polymer, increasing the thickness of theNafion R© film, changing the electrode materials or solvent, etc.On the other hand, the performance of an IPMC can vary withits thickness, the bending stiffness and electric field of theNafion R© film can be affected by the thickness of the IPMC.In this study, the IPMC is fabricated with a Nafion R© filmwith a novel structure of gradient in thickness. The filmswith a uniform structure and different gradient structures arecast by the same volume of Nafion R© dispersion. The gradientIPMC which was fabricated by electroless plating is used todetermine how the performance changes. The deformationdisplacement test and blocking force measurement under ACand DC voltage are compared between uniform and gradientstructure in this paper.2. Experiment2.1. Casting gradient filmsTypically, the commercialized ion exchange polymerNafion R© film from DuPontTM is used to fabricate the IPMC.The performance of the IPMC varies with its thickness,such as deformation, blocking force etc. The commerciallyavailable Nafion R© film is uniform with thickness varyingfrom 20 to 183 µm [24]. To achieve the desired gradientNafion R© film, the casting method with Nafion R© dispersionfrom DuPontTM is used in this work. The casting procedureof gradient Nafion R© film is illustrated in figure 1.Nafion R© dispersion and dimethylformamide (DMF)are poured into the casting mould with dimensions of50 mm × 15 mm × 40 mm (length × width × height). Thevolume of the Nafion R© dispersion (D520, polymer content5 wt%) is 15 ml and the volume of DMF is 1/4 of that ofthe Nafion R© dispersion. The use of DMF is to prevent surfacecracks in solidified Nafion R© during solvent evaporation.Tetraethylorthosilicate (TEOS) is another additive to improvethe intensity and keep the internal water molecules of theIPMC. The amount of TEOS is 5% of whole solution byweight.Next, the mixed solution is stirred with a magnetic stirrerto make the solution homogeneous (sometimes ultrasoniccleaner is used to eliminate bubbles in this step). The solutionis then placed in a constant-temperature drying oven. In orderto cast the gradient film, the casting mould is placed at a tilt.The mould must be keep level to get the uniform film. Thesolvent is fully evaporated at 70 ◦C in the oven. It takes almost20 h to form the film; the temperature is then raised to 100 ◦Cfor 3 h to improve the mechanical stiffness of the film andanneal at 140 ◦C for 15 min to relieve the stress in the film.Finally, the gradient Nafion R© films are cast and conserved inde-ionized water.2.2. Fabrication of the IPMCThe electrodes of Pt attached to both sides of the castNafion R© film are fabricated by electroless plating. Theelectroless plating method is as follows: First, 1500#sandpaper is used to roughen the surface of the film alongone direction to increase the interfacial area so that it wouldhelp the electrodes material deposits. Then the film is rinsedchemically with H2SO4 (0.5%) and H2O2 (15%) solution;afterwards, the film is rinsed with boiled de-ionized waterand dipped into H2SO4 (0.5%). Second, the film is dippedinto the solution of [Pt(NH3)4]Cl2 (3 mg mm−2) for about14 h to accomplish ion exchange. Third, the platinum complexcations are reduced to the metallic state by using the reducingagents NaBH4 (5%); the reaction temperature is from 40 to60 ◦C. Then the Pt is deposited on the surface of the film.Fourth, the film is prepared for the second reduction reactionby rinsing in ultrasonic cleaners after the first reductionreaction. Fifth, the solution of hydrazine hydrate (20%) andthe solution of hydroxylammonium chloride (5%) are used toperform the second reduction as the reducing agents. Afterthis reduction, the IPMC sample is fabricated. Then the IPMCsample is rinsed with de-ionized water and stored in a solutionof LiCl for experiment.2Smart Mater. Struct. 22 (2013) 115035 Y Zhao et alFigure 2. Deformation displacement test system.Figure 3. Blocking force measurement system.2.3. Experimental setupThe main performance characteristics of IPMC are de-formation displacement and blocking force. Therefore, thedeformation displacement test system and the blockingforce measurement system is established, respectively. Theexperimental setup of the deformation displacement testsystem is shown in figure 2. The IPMC is gripped in frontof the coordinate paper (1 mm × 1 mm per grid), theactuated deformation process is captured by digital camera,and then the displacement data is acquired by an imageprocessing system in a PC. The experimental setup of theblocking force measurement system is shown in figure 3. Theblocking force is measured by a load cell (XH10-5g) and dataacquisition is by National InstrumentsTM PXI system withPXIe-6361(DAQ). The solid arrow line stands for ‘actuatedby AC voltage’ of the waveform generator (Agilent 33522A).The dotted arrow line stands for ‘actuated by DC voltage’ ofthe DC power supply.3. Results and discussionOne uniform Nafion R© film and two different gradient filmswere cast to fabricate the IPMC. The thickness was 0.42 mmuniform, 0.37–0.47 mm and 0.22–0.54 mm, respectively.The average thickness of the films was nearly 0.42 mm.The schematic of IPMCs cast with different gradient inthickness is illustrated in figure 4. 1#, 2#, 3# stand for the3Smart Mater. Struct. 22 (2013) 115035 Y Zhao et alFigure 4. Schematic of the cast Nafion R© film with differentgradient.IPMC with thickness of 0.42 mm uniform, 0.37–0.47 mm,0.22–0.54 mm, respectively. After electroless plating platinumas the electrodes of the IPMC, the edges of the the IPMC needto be cut away otherwise it would cause a short circuit. TheIPMC was cut away around the edge by a pair of scissors. Thedimension of each IPMC is 35 mm × 7 mm for testing.In the displacement test, the IPMC was clamped bythe thick end. The length of the IPMC is 30 mm outsideof the clamp. The IPMC was actuated under 0–3.5 V DC.Deformation images of the IPMC with different gradientswere recorded in figure 5. Obviously, the deformation of2# IPMC almost reaches 90◦ under 3.5 V DC.Figure 6 shows the deformation displacement of eachIPMC under 0–3.5 V DC. The result in figure 6 shows thatthe deformation displacement of gradient IPMC is almostsimilar to the uniform IPMC below 3 V. When the drivenvoltage was 3.5 V DC, the displacement of 2#IPMC wasalmost 40 mm which is better than that of the uniform IPMC.2#IPMC exhibits the best deformation performance driven byDC voltage.A 0.1 Hz and a 0.5 Hz sinusoidal input voltage withan amplitude that varied from 0 to 3.5 V at 0.5 V intervalswas applied to the IPMC. The displacement of the IPMC ismeasured between the upper and lower positions. The resultof displacement of the IPMC driven by AC voltage is shownin figures 7 and 8, respectively. Remarkably, the deformationdisplacements of gradient IPMCs are better than that of theuniform IPMC. Furthermore, the deformation displacementdriven by low frequency is better than high frequency ofthe sinusoidal wave and the displacement decreases as thefrequency increases. The maximum displacement of gradientIPMCs driven by an AC voltage was almost 17 mm at0.1 Hz with the amplitude 3.5 V which is two times largerFigure 5. The deformation of the IPMC under 0–3.5 V DC: (a) 1# IPMC; (b) 2# IPMC; (c) 3# IPMC.4Smart Mater. Struct. 22 (2013) 115035 Y Zhao et alFigure 6. The deformation displacement of IPMC under 0–3.5 VDC.Figure 7. The deformation displacement of the IPMC under 0.1 Hz3.5 V.than the displacement generated by the uniform IPMC. Fromthese results of the displacement test, although the averagethickness of the gradient and uniform IPMC are the same,the bending stiffness of the forepart of the gradient IPMC islower than that of a uniform IPMC. Therefore, the forepartof the gradient IPMC is easy to deform and exhibits betterperformance of deformation than that of the uniform IPMC.Figure 9 shows the result of blocking force measurementunder 0–3.5 V DC. The blocking force of the IPMC under a0.1 Hz and 0.5 Hz sinusoidal input voltage with amplitudevarying from 0 to 3.5 V at 0.5 V intervals is shown infigures 10 and 11, respectively. The blocking force of theIPMC keeps increasing with increase in the DC voltage. Theblocking force of gradient IPMCs is much better than thatof the uniform IPMC. The maximum of gradient IPMCs isalmost two times larger than that of the uniform IPMC. Infigure 9, the blocking force of 2# IPMC began to decrease at3.5 V, which is caused by the relaxation back phenomenon(perhaps caused by the effects of the fabrication process).When the AC voltage is applied to the IPMC, the gradientFigure 8. The deformation displacement of the IPMC under 0.5 Hz3.5 V.Figure 9. The blocking force of the IPMC under 0–3.5 V DC.IPMCs also show better performance of the blocking forcethan the uniform IPMC. Meanwhile, low frequency voltageresults in a larger blocking force than high frequency voltagebecause the IPMC has more time to reach the maximum ofthe blocking force. The gradient structure makes the bendingstiffness different along the gradient direction. The clampingend of the gradient IPMC is thicker than that of the uniformIPMC, and it provides higher bending stiffness and elasticpressure; as a result it generates a higher blocking force.4. ConclusionsIn this study, a novel structure of cast Nafion R© film isproposed to fabricate an IPMC with a gradient in thicknessby using electroless plating. Three Nafion R© films werecast with thickness 0.42 mm uniform, 0.37–0.47 mm and0.22–0.54 mm, respectively. By using these Nafion R© films,the IPMCs were fabricated with the dimension of35 mm × 7 mm. The experiments of displacement testand blocking force measurement were carried out to verify5Smart Mater. Struct. 22 (2013) 115035 Y Zhao et alFigure 10. The blocking force of the IPMC under 0.1 Hz 3.5 V.Figure 11. The blocking force of the IPMC under 0.5 Hz 3.5 V.how the performance changes for practical use. The resultsshow that the performance of the IPMC is improved both indeformation displacement and blocking force with a gradientstructure in thickness. The low bending stiffness in theforepart of the gradient IPMC makes it easy to deform andgenerates a larger displacement than the traditional uniformIPMC, while the bending stiffness is high near the clampingpart and that is good for higher blocking force output.Therefore, gradient IPMCs would be further studied andwidely used as actuators or sensors in smart materials andapplications. Additionally, it is essential to investigate theinfluence of gradient changes on properties of IPMCs in futurestudies.AcknowledgmentsThis work is supported by Natural Science Foundation ofFujian Province of China (No. 2011J05140), FundamentalResearch Funds for Central Universities of Xiamen University(No. 2011121045).References[1] Shahinpoor M 2003 Electrochim. Acta 48 2343–53[2] Shahinpoor M and Kim K J 2004 Smart Mater. 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Improving the performance of IPMCs with a gradient in thickness

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Improving the performance of IPMCs with a gradient in thickness

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