Water uptake and migration effects of electroactive ion-exchange polymer metal composite (IPMC)...

Sensors and Actuators A 118 (2005) 98–106

Water uptake and migration effects of electroactive ion-exchangepolymer metal composite (IPMC) actuator

Jun Ho Leea, Jong Hoon Leea, Jae-Do Nama,∗, Hyoukryeol Choib, Kwangmok Jungb,Jae Wook Jeonc, Young Kwan Leed, Kwang Jin Kime, Yongsug Takf

a Department of Polymer Systems Engineering, Intelligent Microsystem Research Center (IMSRC), Sungkyunkwan University, Suwon 440-746, South Koreab School of Mechanical Engineering, Intelligent Microsystem Research Center (IMSRC), Sungkyunkwan University, Suwon 440-746, South Korea

c School of Information and Communication Engineering, Intelligent Microsystem Research Center (IMSRC), Sungkyunkwan University,Suwon 440-746, South Korea

d Department of Chemical Engineering, Intelligent Microsystem Research Center (IMSRC), Sungkyunkwan University, Suwon 440-746, South Koreae Active Materials and Processing Laboratory (AMPL), Mechanical Engineering Department and Nevada Ventures Nanoscience Program,

University of Nevada, Reno, NV 89557, USAf Department of Chemical Engineering, Inha University, Inchon 402-751, South Korea

Received 19 July 2003; received in revised form 1 July 2004; accepted 5 July 2004Available online 10 August 2004

A

y attractivef ed to be thei fluorinateds ochemicala free watera ry (CLT), am opic IPMCt PMC wasq©

K

1

bteset

the, re-n aateduceardsdandreas

, dis-ula-ver,

0d

bstract

The low actuating voltage and quick bending responses of ion-exchange polymer metal composite (IPMC) are considered veror the construction of various types of actuators and sensors. The principle of IPMC actuation under electric field has been believon cluster flux and electro-osmotic drag of water from the anode to cathode direction through the hydrophilic channels in the perulfonic acid polymer chains. In this study, the effect of water content residing in the perfluorinated polymer was investigated by electrnd thermal experiments as well as hydraulic mechanical modeling. The water residing in the IPMC actuator seemed to exist asnd bound water, each corresponding to interstitial and hydrogen-bonded water molecules. Using the classical lamination theoodeling methodology was developed to predict the deformation, bending moment, and residual stress distribution of the anisotr

hin-plate actuators. In this modeling methodology, the internal stress evolved by the unsymmetric distribution of water in the Iuantitatively calculated and subsequently the bending moment and the curvature were estimated for the IPMC actuator.2004 Elsevier B.V. All rights reserved.

eywords: Ion-exchange polymer metal composite (IPMC); Water migration; Actuator; Classical lamination theory

. Introduction

Electro-active polymer (EAP) systems are considered toe promising candidates for dynamic sensors, robotic ac-

uators, and artificial muscles. A composite form of ion-xchange polymer film with metal electrodes has been exten-ively investigated because of its balanced mechanical prop-rties with fast response and large deformation[1,2]. When

he electric field is applied to the ion-exchange polymer metal

∗ Corresponding author. Tel.: +82 312907285; fax: +82 312928790.E-mail address:[email protected] (J.-D. Nam).

composite (IPMC), the ions move from one surface toother electrode surface in the form of ion-water clusterssulting in a bending motion of the composite film. Whevoltage is applied in the range of 1.0–10.0 V to a hydrIPMC, the large ionic conductivity is considered to indthe electro-osmosis resulting in a bending of the film towthe positive electrode (anode)[3–7]. Due to its distinguishecharacteristics of low driving voltage, rapid response,actuation capability in water, it has been applied to the aof artificial muscles/actuators/sensors, active cathetertributed actuation device, underwater robot, micromaniptors, micropump, face-type actuator, wiper of asteroid ro

924-4247/$ – see front matter © 2004 Elsevier B.V. All rights reserved.oi:10.1016/j.sna.2004.07.001

J.H. Lee et al. / Sensors and Actuators A 118 (2005) 98–106 99

etc.[2,5–12]. Actual mechanism of IPMC is still argumenta-tive, but it seems that the mobility of ion-water clusters causesan expansion of one side of the polymer and an equivalentcontraction of the other side. Therefore it is one of the keyissues in IPMC actuator application and utilization to under-stand the water migration phenomena related to the mechan-ical configuration of the IPMC layers and the applied electricfield.

The ion-exchange polymers, collectively used in the IPMCsystem, have been applied in various fields such as elec-trochemical processes, catalysis, and polymer electrodes[12–18]. Nafion® and Flemion® are the common mem-branes used for the actuator/sensor application with fluo-rocarbon backbones and mobile cations (counter ions). Forexample, Nafion is a copolymer of tetrafluoroethylene andsulfonyl fluoride vinyl ether, which contains the hydropho-bic fluorocarbon and hydrophilic ionic phases resulting ina phase-separated morphology of distinct hydrophobic andhydrophilic regions. The ionic-exchange sites are likely toaggregate to form a tightly packed region often referred to asclusters, which are interconnected and readily saturated bywater[19–24]. In various modeling and experimental works,the phase-separated domains has been assumed to be spher-ical inverted micellar structures connected by short narrowchannels[20,25,26].

d ont oly-m r. Inf osti dis-t MCa hy-d ibu-t t ofw ruc-t de-f onlyt ani-c merfi t ofm lay-e

wase culem assi-c om-p them istri-b dis-t

2

uo-r and

dry thickness of 0.178 mm), was purchased from DuPont deNemours and used for the IPMC actuator. The electrode plat-ing of the Nafion was implemented by using the modifiedmethods originally developed by Takenake et al.[27], Milletet al. [28,29] and others[30]. Tetraamineplatinum(II) chlo-ride, [Pt(NH3)4]Cl2, and sodium borohydride were used forimpregnation and reduction processes as precursor salts formetallic Pt precipitation and reducing agent, respectively. Theimpregnation/reduction process was repeated up to one toeight times to control the thickness of the electrode. Prior toplating, the membranes were boiled in deionized water for1 h, and dried overnight in a vacuum oven at 80◦C. The dryweight of the Nafion was measured to establish the platinumloading.

The strain and the force of the IPMC actuator were mea-sured by a laser strain gauge (LK-081) and force sensor GSO-30 connected to 12 bit A/D converter for data analysis and 12bit D/A converter for voltage control. The specimen used tomeasure the bending moment and curvature was 20 mm longand 5 mm wide. The differential scanning calorimetry (DSC)instrument used in this study was TA Instruments DSC 910and the experiments were performed in nitrogen environmentat 10◦C/min. The current density of the IPMC actuators wasmeasured by potentiostat/galvanostat (Perkin-Elmer 263A)at different frequencies of applied voltage for the specimensc

3

3

ateri ningc n oft and8 pec-t mera ound

F eachr

However, there is no experimental evidence reportehe water migration or distribution inside perfluorinated per film in such a dynamic situation as an IPMC actuato

act, it may be more reasonable to mention that it is almmpossible to quantitatively measure the concentrationribution of water and/or ions during the movement of IPctuators. Accordingly, it is desirable to investigate theraulic bending motion based on a simplified water distr

ion by using a mechanistic model to identify the effecater migration on the bending motion of the laminate st

ure of IPMC. The bending moment (or force) and theormation of the IPMC actuator are associated with nothe amount of water migration but also with such mechal/physical properties as the modulus of hydrated polylm, the modulus of platinum, the expansion coefficienoisture, and the geometric arrangement of compositers.

In this study, the effect of water content and migrationxperimentally investigated to envisage the water moleovement during IPMC actuation. Subsequently, the cl

al lamination theory (CLT) was applied to the layered cosite structure of the IPMC actuator in order to evaluateechanical moment, deformation, and residual stress d

ution, which were merely caused by the concentrationribution of water in the ion-exchange polymer film.

. Experimental

The copolymer of tetrafluoroethylene and sulfonyl flide vinyl ether, Nafion 117 (equivalent weight of 1100

ontaining different water contents.

. Results and discussion

.1. Thermal and electrical response of IPMC actuator

Fig. 1shows the melting and vaporization peaks of wn the IPMC actuator measured by the differential scanalorimetry (DSC). As can be seen in the melting regiohe specimen, two distinct melting peaks occur at 0.8.0◦C, seemingly representing free and bound water, res

ively. The free water resides in the free volume of polynd freezes at the usual freezing point of water, but the b

ig. 1. DSC thermogram of IPMC actuator showing two melting peaksepresenting free- and bound-water.

100 J.H. Lee et al. / Sensors and Actuators A 118 (2005) 98–106

Fig. 2. SEM micrographs of fractured IPMC actuators after (a) single deposition and (b) fourth depositions of platinum exhibiting different thickness ofelectrode on Nafion surface.

water is bonded to the polymer chain by the hydrogen bondand tends to affect the main mobility of polymer chains andthus transport properties like permeability[31,32]. Accord-ingly, the IPMC actuation is more likely associated with thebound-water uptake and its transport phenomena since theIPMC actuator is basically controlled by the water migration,which is induced by electrical potential. From this prelimi-nary DSC results, it seems evident that the water in perfluori-nated polymer may exist in two different forms, each possiblyplaying different roles in IPMC. According to the previousworks, the temperature dependence of these two waters isopposite: The equilibrium absorption of bound water in poly-mers decreases with increasing temperature, but the amountof free water increases with temperature, which should beconsidered in the IPMC applications in cryogenic conditions[31–33]. It may be reasonable to mention that these two wa-ters could be affected by the applied electrical potential be-cause the hydrogen bond strength and the thermodynamicaffinity of water molecules to the polymer chain could be in-

actuat

fluenced by the electrostatic force and dynamic shear stressesinduced by water migration. Further study should be per-formed to identify the effect of two distinct waters in IPMCactuation.

Fig. 2shows the platinum electrodes deposited on the sur-face of Nafion. The electrode shows a smooth thin layerat ca. 7�m of electrode thickness after a single deposi-tion, and ca. 14�m after four times deposition. However,it should be mentioned that the platinum is gradually de-posited further inside Nafion membrane by the repeatedphysical impregnation and chemical reduction processes dur-ing the electrode plating, which may not be clearly seenby SEM. The gradual distribution of platinum metal de-posited in the Nafion membrane in the through-the-thicknessdirection may give a gradual distribution of water solubil-ity of Nafion polymer. Accordingly, the modulus of theplatinum-deposited Nafion would change gradually, whichmay also affect the stress distribution and finally the per-formance of IPMC actuator. The platinum layer is observed

Fig. 3. Strip-type IPMC
or bending motion at 1.5 V.


Fig. 4. IPMC bending motion exhibited by the curvature of strip-type actu-ators for different number of electrode deposition times (actuated at 1.5 V).

to cover the Nafion surface well without significant surfacecracking.

Although the prepared electrode after a single depositioncovers the Nafion surface well, the electrical resistance ofsuch a thin electrode in the in-plane directions is too highto allow the electric current to reach the remote areas fromthe electrical source in practical application of centimeter-size IPMC actuators. From a mechanical point of view, a thinelectrode is preferred to a thick electrode because the forcerequired to actuate the thin electrodes by water migrationwould be lower than the thick ones. Conclusively, the opti-mal electrode thickness would be determined by the surfaceresistance and electrode stiffness.

Applying electrical potential across the IPMC thickness,the actuator bends to positive electrode (anode) because of thedynamic migration of water in the form of cationic clusters.Fig. 3shows a typical bending motion of the IPMC actuator.As can be seen the IPMC actuator gives a large deformation ina high frequency range up to 30 Hz, which may be consideredhigh enough to be used as a aerodynamic wing application.Such IPMC bending motion is reproducible and durable forseveral hours until all the water molecules are depleted. Thebending speed and displacement are dependent on variousfactors such as applied voltage, water content, surface resis-tance, electrode thickness, etc.

f de-p ctu-a att hedw tedc sitionf oesn imes.A ode-d sionfl r. Ast trodei thosec th the

repeated plating giving a slow deposition rate. Subsequently,there may be a critical number of plating, which practicallylimits the efficiency of the chemical deposition. The increasedthickness of electrode may well increase the stiffness of theactuator, which restricts the extent of bending deformation.It will be discussed later in the modeling study.

Using the fabricated IPMC actuators, the electrical currentwas measured as a function of time for different frequen-cies of applied voltage.Fig. 5 shows the current responseat different frequencies: 2.0, 10.78, and 15.78 Hz. When theelectric potential is applied to IPMC actuator, the electriccurrent increases immediately to the maximum because thecations move from the positive electrode (anode) to nega-tive electrode (cathode) by the electrostatic force. The wa-ter molecules are usually clustered with the cations and thusare forced to move with the positive ions in the direction tothe negative electrode, which results in a bending motion ofIPMC. A limited number of mobile cations are included inthe ion-exchange membrane and thus the increased currentresultantly decreases to zero while the voltage is maintained.When the frequency of the applied electrical potential is low,as seen inFig. 5(a), the electric current reaches zero beforethe voltage is reversed. However, when the frequency is rel-atively high as inFig. 5(b) and (c), the current is quicklyreversed before it reaches zero. It has been reported that thee s ofe ion-c ert rt dif-f enceo e ofc thatt nts.

c-i uredi rea)o val-u massfl vest tenti ntial.T atd nt inF reasei thea ur-r d fort n thea

b muma hent gin-n aterm oulds er is

For the electrodes prepared by different numbers oosition, the dynamic actuation behavior of the IPMC ator can be seen inFig. 4. The IPMC curvature shows th

he equilibrium position of bending deformation is reacithin 1 s for all the specimens in this study. The equilibraurvature increases with the numbers of electrode deporom the first to the fourth plating, but the curvature dot seem to increase by the repeated plating over four ts with most chemical deposition methods, the electreposition method used in this study depends on the diffuux of the electrolyte and reducing agent into the polymehe plating is repeated, the thickness of the metal elecncreases and therefore the concentration gradient ofhemicals across the platinum electrode decreases wi

lectrical current exhibits two major competing processelectrostatic movement of ions and diffusive transport oflustered water molecules[12]. It is reasonable to considhat the accumulated water molecules in the cathode stausing back to the anode due to the concentration differf water, which is likely to affect the capacitive responsurrent as a function of time. It should also be mentionedhe electrolysis of water could take place in this experime

Fig. 6shows the cyclic voltamogram (CV) of IPMC spemens containing different levels of water content measn air. The current density (current divided by the IPMC af IPMC containing higher water content shows higheres of current density, which may be ascribed to higherux of ion/water clusters in perfluorinated polymer. It prohat the electrical current is proportional to the water conn the electrolyte polymer under the same electrical poteaken from the CV results ofFig. 6, the current densityifferent voltages is plotted as a function of water conteig. 7. As can be seen, the current density seems to inc

n proportion to water content and it also increases withpplied voltage. A quantitative correlation of electrical cent with water content can be obtained and further usehe actuator control modeling and performance design ipplication of various micro robot systems.

The IPMC performance can be seen inFig. 8 in terms ofending moment. The bending moment shows a maxifter about 40–50 s of operation at 0.1 Hz and 1.5 V. W

he IPMC actuator is fully saturated with water at the being of actuation, it is reasonable to consider that the wolecules, which are forced to move to the cathode, w

mear out of the negative electrode because the polym


Fig. 5. Current response of IPMC actuator for square-type voltage application measured at different frequencies at (a) 2 Hz, (b) 11.5 Hz, and (c) 15.5 Hz.

Fig. 6. Cyclic voltamogram of IPMC actuator at different water contentsranging from 85.9% to 100% measured at 500 mV/s.

Fig. 7. Current density plotted as a function of water content in IPMC actu-ator at different voltages.


Fig. 8. Mechanical moment produced by IPMC strips at different lengths(1.5 V and 0.1 Hz).

already saturated up to the maximum amount of absorption.It can be easily validated by visual examination of IPMCelectrodes during actuation especially in the early stage ofoperation. During this early stage of operation, extra wateris vaporized on the electrode surface, and thus the Nafionthickness is decreased with the decreased water content. Itmay be simply reasoned from the mechanical point of viewby the fact that the thin plate gives higher bending moment.Passing the maximum point, the bending moment graduallydecreases with actuation due to the natural vaporization andelectrolysis reaction of water.

3.2. Classical lamination theory

The overall behavior of multi-layer laminate is determinedby the properties of individual layers as well as the stackingsequence of layers often containing anisotropic characteris-tics of physical properties. The so-called classical lamina-tion theory (CLT) predicts the mechanical behavior of thelaminate composed of multiple layers containing differentanisotropic properties[34–37]. The CLT is based on the as-sumption that the lateral dimensions of the lamina are muchlarger than its thickness and the laminates are loaded in itsplane only, say, in a state of plane stress. Additionally assum-i thet , thec d fort CLTc e en-v evel-o nates

, thes d toa

as

σx

σy

τxy

k

=

Q̄11 Q̄12 Q̄16

Q̄12 Q̄22 Q̄26

Q̄16 Q̄26 Q̄66

k

ε0x

ε0y

γ0xy

+ z

Q̄11 Q̄12 Q̄16

Q̄12 Q̄22 Q̄26

Q̄16 Q̄26 Q̄66

k

kx

ky

kxy

k

(1)

where[Q̄

]is the stiffness matrix calculated by engineering

constants in two-dimensional case: two tensile moduli in thex-and y-directions, shear modulus, and Poisson ratio. Thestrain is defined by centerline strain (ε0

i ) and curvature (ki) asa function of the distance from the center (z) as{εx, εy, γxy} ={ε0

x, ε0y, γ

0yx} + z{kx, ky, kxy}. The detailed relations between

the matrix entries and the engineering constants can be foundelsewhere[34–37].

Eq. (1)indicates that the strains in the laminate vary lin-early across the thickness. Therefore, the variation of stressthrough the laminate thickness is obtained by calculating thestress variation in all the laminae. The resulting forces (N)and moments (M) acting on the laminate may be definedby integrating the corresponding stress and moment throughthe laminae thickness. The integration through the wholet ayer[ g-m picl{

w(al

mi-n build-u bodya ges.T nto inw att mo-m , andt notc odesa e ind uldb s arei them ses ina cesso rainst red to

ng that the in-plane displacements vary linearly throughhickness of the laminate usually for small displacementlassical lamination theory has been successfully utilizehe analysis of thin layered composite structures. Thean also be applied for the various thermal and moisturironments, which usually induce the residual stress dpment and the resultant deformation of the whole lamitructure.

For two-dimensional case in the state of plane stresstress–strain relation for an orthotropic lamina referrerbitrary axes may be expressed for thekth ply of laminate

hickness may be obtaind by integrating each distinct l36–37]. Writing the resulting equation in the form of auented matrix, the constitutive relation for the 2D orthotro

aminate may be expressed as follows:

N

M

}=

{A B

B D

} {ε0

k

}(2)

here Aij = ∑nk=1(Q̄ij)k(hk − hk−1), Bij = (1/2)

∑nk=1

Q̄ij)k(h2k − h2

k−1), Dij = (1/3)∑n

k=1(Q̄ij)k(h3k − h3

k−1),ndhk is the distance from the centerline to the top ofkth

amina.A change in temperature or moisture distribution of la

ates causes a dimensional change and residual stressp because the hydraulic strains are developed in thes a result of hydraulic and/or thermal distribution chanhe hydraulic strain,εH, is equal to the product of coefficief moisture expansion (β) of the laminae and the changeater content (C), viz.:εH = βC. It should be mentioned th

he hydraulic strains do not produce a resulting force orent when the body is completely free to expand, bend

wist. However, the individual lamina in the laminate isompletely free to deform. For example, the metal electrttached to the perfluornated polymer would not changimension by water uptake and thus the polymer film woe highly restricted in deformation. The lamina stresse

nduced by the constrains placed on its deformation byetal electrode and adjacent laminae. In fact, the streslamina are produced only by the strains that are in ex

f the hygrothermal strains for its free expansion. The sthat would cause stress in the laminate are usually refer


as the mechanical strains,εM given by

{εM} = {ε} − {εH} (3)

In the case of hydraulic deformation, there are no externalforces or moments applied to the laminates but the stress isgenerated by the hydraulic distribution inside of the laminate.Thus, substituting the above mechanical strain intoEq. (2)and equating the resulting forces and moments to zero, thefollowing equations are obtained:{

A B

B D

} {ε0

k

}=

{NH

MH

}(4)

where

{NT} = C

n∑k=1

{Q̄}k{β}k{hk − hk−1} (5)

{MT} = 1

2C

n∑k=1

{Q̄}k{β}k{h2 − h2} (6)

where{NH} and {MH} are fictitous forces and moments,sometimes called the hydraulic forces and moments, and theyeventually create laminate deformation. When the hydraulicstate of the laminate differs from its stress-free state, the hy-draulic force and moments are induced by the laminate. Ino i-c ce as

3

s ont ght,c icalr t al.i

E

w ft oly-m ond er.E Thea nstan[ -l ss ofN 178t ely,r n[m 16%o

om-p wa-

ter drag force, swelling and contraction of membrane, electro-static force and conformation change of perfluorinated poly-mer[1,2,5,6,12,38]. As a result these effects, the actuation ofIPMC is created by the unsymmetric distribution of water in-side the perfluorinated polymer. It should be mentioned thatthe unsymmetric water content provides different modulusvalues and swelling ratio (or thickness) of Nafion film in thethrough-thickness direction. Several models have been pro-posed to predict the ionic concentration and water distributionin the polymer as well as mechanical deformation and forcesof IPMC [12,38,40–41]. However, different researchers haveprovided different formulation and different prediction ofwater and ion concentration distributions. Furthermore, thepredicted ion-cluster and water distributions have not beenvalidated by experiments. Without this experimental data, itmay simply be assumed that the water concentration linearlydecreases from a maximum at the negative electrode to a min-imum at the positive electrode. Based on the assumed water-concentration distribution, the model equations may be usedto investigate the effects of water migration on IPMC actua-tion forces and deformation. In applying the CLT to the IPMCsystems, the perfluorinated polymer film was discritized intomany hypothetical layers each containing different values ofwater content in a linear fashion and different modulus valuesby Eq. (7).

wasa eachc nc-t -o re lit-t udy.T ounto odes sim-p rc n thew s alsoa fion

F migra-t enerateda

ther word, the{NH} and{MH} are equal to the mechanal force and moment for the fixed-end actuator to produtrain equal to the hydraulic strain of the laminate.

.3. CLT application to the IPMC actuator

The tensile modulus of perfluorinated ionomer dependhe variation of cluster diameter with the equivalent weiation form and water content of the polymer. An empirelation of hydrated Nafion polymer proposed by Grot es [13]

= E0 exp

[−α

{f + 1200− Ew

20

}](7)

hereE0 = 0.275 GPa,α = 0.0294,f is the water content ohe swollen polymer in grams of water per 100 g of dry per (f = 100C), C is the fractional weight of water basedry Nafion, andEw is the equivalent weight of the polymw of Nafion 117, which was used in this study, is 1100.verage Poisson ratio is assumed to be 0.487 as a co38]. The coefficient of moisture expansionβ can be calcuated by the maximum water uptake and swollen thickneafion 117. The thickness of Nafion 117 changes from

o 202�m with 0% and 16% of water uptake, respectivesulting inβ = 0.8425C in the unit of strain/water fractio39]. Accordingly, it can be estimated byEq. (7) that theodulus decreases from 0.225 to 0.15 GPa at 0% andf water content, respectively.

The IPMC actuator motion is associated with various clex phenomena such as ionic motion by electric field, the

t

In this study, the perfluorinated polymer (Nafion 117)ssumed to consist of 20 layers with equal thickness,ontaining different water content varying linearly as a fuion of distance fromCmax at the cathode andCmin at the ande. When the number of layers were over 20, there we

le difference observed in numerical calculation of this sthe amount of water migration may be defined as the amf water moving from the equilibrium state to the electride due to the applied electric potential and thus canly be calculated as 0.5Cmax for a linear distribution of wateoncentration as assumed in this study. Depending oater content of the actuator, the actuator thickness wadjusted by the coefficient of moisture expansion of Na

ig. 9. Calculated residual stresses in IPMC actuator created by waterion where two residual stresses at the ends represent the stresses gt the platinum electrodes.


Fig. 10. Calculated curvature of IPMC strip plotted as a function of watermigration.

film, β = 0.8425C. The model equations (1)–(7) were solvedfor the 20 layers of hypothetical layers of Nafion and twolayers of platinuum electrodes.

Fig. 9 shows the model prediction of residual stress dis-tributed in the IPMC at the state of actator bending. Thestresses at the far ends of IPMC laminate represent those atthe platinum electrodes, represented by different signs corre-sponding to the compressive and tensile stress modes, or viceversa. As can be seen, the high residual stresses are createin the metal electrodes because the modulus of platinum ismuch higher than perfluorinated polymer and thus most stressin the metal electrodes is developed by bending motions. Thestress created in polymer near the metal electrode shows anopposite sign of stress to the electrode because the polymer isrestricted by the Pt electrode and cannot deform as much as itcan in the free state. It is reasonable that the residual stressedeveloped in the Nafion film gradually decreases from theelectrode to center.

As seen inFig. 10, the bending curvature of IPMC can bepredicted by the model as a function of water migration. Ac-cording to the model prediction, ca. 3.5% of water migrationcreates a curvature up to 0.25 cm−1, which is in the praticalrange of IPMC actuation as shown inFig. 3. The predictedbending curvature increases with the amount of water migra-tion, which has been observed by experiments at differentc de-v theq ac-t ther ce ofI

4

tionw entsa per-

formance was related to the surface resistance of platinumelectrode and water migration. Using the classical laminationtheory (CLT), the deformation, bending moment, and resid-ual stress distribution of the IPMC actuator was quantitativelycalculated, and the model prediction was compared well withpractical observation and experimental results demonstratingthe validity of the developed modeling methodology.

Acknowledgements

This work was supported by a grant from the Korea Re-search Foundation (KRF-2001-005-E00006). The authorsalso appreciate the instrumental support from the IntelligentMicrosystems Research Center (IMSRC) at SungkyunkwanUniversity in the 21C Frontier R&D Program.

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.en-

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[[[[ .[[ . 19

[[ ess,

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[ 01.[ em.

[ Hy-

[ 89)

onditions of water content and frequency. Overall, theeloped model demonstrates its capability of predictinguantity of water migration needed for IPMC bending

uation. It also demonstrates that the water migration inange of a few percentages could be the real driving forPMC bending actuation.

. Conclusions

In this study, the water content effect of IPMC actuaas investigated by electrochemical and thermal experims well as hydraulic mechanical modeling. The IPMC

d

s

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Biographies

Jae-Do Namis a professor at the Department of Polymer Science and En-g andM and1 ing att oly-m earcha sungG 994.H s, or-g rs andc

Y ent atI l En-g PhDf sameu 994)a s Co.,SK alS

K eer-i Lab-o tedf PhDf ater,h nergyE in-d lectric

Devices, Inc. (1995–1997) and chief scientist at Environmental Robots,Inc. (1997–2001), Albuquerque NM. He has published over 120 tech-nical papers and holds two patents. His research and teaching interestsare broad based, but mainly in artificial muscles/active materials/sensors,thermal sciences/energy systems, and nanotechnology. He is a recipientof the 2002 Ralph E. Powe Junior Faculty Enhancement Award fromOak Ridge Associated Universities and the 1997 Best Paper Award ofASME/Advanced Energy Systems/HPTC. Currently he serves as the in-terim director of Nevada Ventures Nanoscience Program (NVNP) and isa board member of Nevada Southwest Energy Program Board.

Hyoukryeol Choireceived the BS degree from Seoul National Universityin 1984, the MS degree from Korea Institute of Science and Technology(KAIST) in 1986, and the PhD degree from Pohang University of Sci-ence and Technology (POSTECH) in 1994, Korea. From 1986 to 1989 heworked as an associate engineer in LG Electronics Central Research Lab-oratory. From 1993 to 1995, he stayed in Kyoto University as the granteeof scholarship from Japan Educational Administry. From 2000 to 2001he visited the Advanced Institute of Industrial Science and Technology(AIST) in Japan. In 1995, he joined the faculty of Mechanical Engineer-ing, Sungkyunkwan University and currently is an associate professor. Hisinterest includes biomimetic actuator and mechanisms, artificial muscleactuator, field applications of robots, etc.

Kwangmok Jungreceived the BS and MS degree in Mechanical En-gineering from Sungkyunkwan University, Korea, in 1991 and 2002,and is currently pursuing the PhD degree in Mechanical Engineering atSungkyunkwan University. He worked for Daewoo Motor Company as anassistant manager from 1995 to 1999. From 2000 to 2003, he had joinedthe Intelligent Micro System Research Center (IMSRC), Korea. His cur-rent research interests focus on the artificial muscle actuator, microrobots,a

J eer-i 986,r urdueU eniorr ed theS iver-s ntly ap s, andf

J t ofP ea, in1 tmento . Hew from2 icroS n thea displaya

J merS a. Her fromS ly. In2 restsc ethanen s.

ineering, Sungkyunkwan University, Suwon, Korea. He received BSS in Chemical Engineering at Seoul National University in 1984986, respectively. In 1991, he received PhD in Chemical Engineer

he University of Washington, Seattle, WA, USA. He worked at the Peric Composites Laboratory, University of Washington, as a resssociate from 1991 to 1993. Returning to Korea, he joined Samroup, in 1993–1994, and moved to Sungkyunkwan University in 1e is actively working in the areas of polymer sensors and actuatoranic/inorganic hybrid nanocomposites, and biodegradable polymeomposites.

. Tak is an associate professor of Chemical Engineering Departmnha University, Incheon, Korea. He received BS and MS in Chemicaineering at Seoul National University in 1984 and 1986. He received

rom Iowa State University in 1992 and worked as a postdoc at theniversity. His industrial work includes a senior researcher (1993–1nd technical consultant (1994–1995) at Samsung Electro-Mechanicuwon, Korea. He serves as the editorial member of theJournal of theorean Corrosion Society, the Journal of the Korean Electrochemicociety, and Metals and Materials International.

wang J. (Jin) Kim is an associate professor of Mechanical Enginng Department and director of Active Materials and Processingratory (AMPL) at University of Nevada, Reno (UNR). He gradua

rom Yonsei University, Korea, in 1987 and received his MS androm Arizona State University in 1989 and 1992, respectively. Le completed a postdoctoral study at Center for Environmental Engineering (CEEE) of University of Maryland-College Park. Hisustrial experience includes senior research engineer at Thermal E

nd biomechatronics.

ae Wook Jeonreceived the BS and MS degree in Electronics Enginng from Seoul National University, Seoul, Korea, in 1984 and 1espectively, and the PhD degree in Electrical Engineering from Pniversity, West Lafayette, in 1990. From 1990 to 1994, he was a s

esearcher at Samsung Electronics, Suwon, Korea. In 1994, he joinchool of Electrical and Computer Engineering, Sungkyunkwan Unity, Suwon, Korea, as an assistant professor, where he is currerofessor. His research interest includes robotics, embedded system

actory automation.

un Ho Leereceived the BS and MS degree from the Departmenolymer Science and Engineering at Sungkyunkwan University, Kor996 and 2000, and is currently pursuing the PhD degree in Deparf Polymer Science and Engineering at Sungkyunkwan Universityorked for Dongjin Semichem Company as an assistant manager002 to 2004. From 2000 to 2002, he had joined the Intelligent Mystem Research Center (IMSRC), Korea. He is actively working ireas of polymer sensors and actuators, photo-resists for flat panelnd biodegradable polymers and composites.

ong Hoon Leeis a research professor at the Department of Polycience and Engineering, Sungkyunkwan University, Suwon, Kore

eceived the BS, MS and PhD degree in Chemical Engineeringeoul National University, Korea in 1989, 1991 and 2001, respective002, he joined Sungkyunkwan University. His current research inteoncentrate on the polymer sensors and actuators, fuel cell, polyuranocomposites, foam and biodegradable polymers and composite

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