1 t c2 f

3Q1

4 of M5 r, M

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7891011121314151617181920 Thermal decomposition

21olym22e (231:224ued25the26ort27osition CS:LiTFSI:DES (14 wt.%:6 wt.%:80 wt.%) exhibiting the ionic conductivity281 at 50 C with activation energy of 8.22 kJ mol1. The relaxation frequency of29

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Journal of Molecular Liquids xxx (2011) xxxxxx

MOLLIQ-03396; No of Pages 4

Contents lists available at SciVerse ScienceDirect

Journal of Mole

.e lUNCOevolved by substituting the synthetic polymer with the natural type, as

in this research corn starch (CS) is used as the replacement.This effort could not be worked out by only utilizing the natural

polymer due to its highly crystalline nature that inhibits its employ-ment in the development of high conducting polymer electrolytes.Thus, CS based polymer electrolytes were developed with the combi-nation of two different materials namely LiTFSI and DES in order toobtain high conducting samples. This contraption was believed toexert applicable electrical and other promising properties as desired.The selected hydrophilic polymer gains its interest due to a number of

This results in the gelatinization of CS as the leaching of amylosefrom the starch granules, evidence the diffusion in the amylosechain [5,6].

The second monomer that needs to be disrupted in order to fur-ther enhance the ionic transport mechanism is the short-chain frac-tion of amylopectin. This monomer was arranged as double helicesin the form of highly crystalline order due to its branching nature[4,7]. Thus, it is not easy to cause disorderliness in the arrangementunless disrupted by negatively charged ions (anions). In order toachieve this, two different types of additives were used to obtainlisted outstanding properties such as its watof renewable resources, low cost, non-toxicnature [13].

Corresponding author. Tel.: +60 3 79674391.E-mail addresses: rameshtsubra@gmail.com (S. Ram

(R. Shanti), ezram@utar.edu.my (E. Morris).

0167-7322/$ see front matter 2011 Published by Eldoi:10.1016/j.molliq.2011.11.010

Please cite this article as: S. Ramesh, et al.,RThe only technique thater electrolytes is throughical. Thus, an effort was

initial step was accomplished upon the heating of CS in distilledwater. The heating procedure makes the starch granules to graduallyswell and undergo disruption into smaller aggregates or particles.can be employed to dispose this type of polymrecycling which is neither practical nor econom1. Introduction

The development of biodegradableattracted scientic and practical interesronmental pollution attributed to thewaste from synthetic polymer electroRECTE

m

plot. The decreasing trends in the melting temperature of polymer electrolytes with increase in DES contentcorrelate to the occurrence of complexation that induces structural disorderliness. The heat-resistivity ofpolymer electrolyte diminishes with the addition of DES and enhancement in the thermal stability was ob-served at the minimum DES content as revealed in TGA analysis.

2011 Published by Elsevier B.V.

er as host material hasent years due to the envi-load of non-degradable

CS is a semi-crystalline polymer composed of both linear amyloseand branched amylopectin chain [4]. In order to enable the naturalpolymer electrolytes to possess high ionic conductivity, the linearmonomer chain arrangement needs to be disrupted as an initial effortallowing the matrix to be present in a highly amorphous state. TheIonic conductivityMelting temperatureDsample DES-80 is log =6.03 Hz, being the lowest relaxation time as revealed by the dielectric loss tangentDeep eutectic solvent was identied for the compvalue of 4.56103 S cmExerted inuence of deep eutectic solvenionic conductivity and thermal behavior o

S. Ramesh a,, R. Shanti a, Ezra Morris b

a Centre for Ionics University Malaya, Department of Physics, Faculty of Science, Universityb Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, 53300 Kuala Lumpu

a b s t r a c ta r t i c l e i n f o

Article history:Received 24 June 2011Received in revised form 14 November 2011Accepted 23 November 2011Available online xxxx

Keywords:

A series of biodegradable puoromethanesulfonyl)imidline chloride and urea withthe CS:LiTFSI matrix was valthat is crucial in enhancingnature of the cation transp

j ourna l homepage: wwwer solubility, availabilityand also biodegradable

esh), shanthy87@yahoo.com

sevier B.V.

J. Mol. Liq. (2011), doi:10.10 PROOF

oncentration in the room temperaturecorn starch based polymer electrolytes

alaya, 50603 Kuala Lumpur, Malaysiaalaysia

er electrolytes were fabricated by utilizing corn starch (CS), lithium bis(tri-LITFSI) and deep eutectic solvent (DES) (synthesized from the mixture of cho-ratio) by solution casting technique. The incorporation of DES in plasticizingprimarily due to its capability in increasing the amorphous elastomeric phaseionic transport mechanism. The conductivitytemperature plot reveals thewhich commensurates with Arrhenius rule. The highest conducting sample

cular Liquids

sev ie r .com/ locate /mol l iq77the anions for the disorderness purpose in this communication. The78rst anion was TFSI obtained from the complete dissolution of LiTFSI79in the polymer matrix. This type of anion is bigger in size thus it can-80not contribute to greater structural disorderness which makes the CS:81LiTFSI polymer electrolytes to exhibit low ionic conductivity.82To further disrupt the branched monomer, another negative83charged ion which is smaller in size is needed to allow it to move in84between the condensed arrangement of atoms more freely and

16/j.molliq.2011.11.010

T85 enhance the amorphous nature in the polymer matrix. The chosen86 anion is chloride (Cl) which is more electronegative than TFSI.87 The Cl ions were obtained from the DES, an ionic mixture synthe-88 sized from choline chloride and urea in a specic ratio [8]. This type89 of ionic mixture gains its interest due to some of its unique properties90 including its unusual solvent property that further dissolves the high-91 ly crystalline CS, its cheap cost compared to the ionic liquid due to the92 low cost of raw materials, ease in the preparation method ignoring93 the purication process and no medium being required, and its94 non-toxic formulation and biodegradable nature [911]. This piece95 of effort enables the DES-plasticized sample to possess high ionic con-96 ductivity required for the application in electronic devices such as97 fuel cells, solar cells, electrochromic windows, and solar-state batte-98

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1312.3. Instrumentation

1322.3.1. Impedance spectroscopy133Impedance measurements were carried out at the temperature134ranging from 50 C to 100 C using HIOKI Model 3532-50 Hi-Tester135over the frequency range of 50 Hz to 5 MHz. The ColeCole imped-136ance plot will be attained upon the completion of the analysis and137this aid in plotting the ionic conductivity and tangent loss plots.

1382.3.2. DSC analysis139The melting temperature of the prepared samples was visualized140by using a METTLER TOLEDO Thermal Analyzer which comprised of141DSC 823e as the main unit and STARE software. The analysis was car-142ried out using an approximate of 5 mg of sample sealed in a 40 l al-143

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2 S. Ramesh et al. / Journal of Molecular Liquids xxx (2011) xxxxxxUNCORREC

ries [1216].In this study, the suppression of the high crystallinity in CS matrix

was scrutinized in terms of the temperature dependent ionic conduc-tivity, dissipation factor and thermal properties.

2. Experimental

2.1. Materials

CS and LiTFSI were purchased from Aldrich and Fluka respectively.The starting materials to synthesize DES are choline chloride andurea, purchased from Sigma. Distilled water is the solvent used to dis-solve all the starting materials.

2.2. Preparation of polymer electrolytes

2.2.1. Synthesizing ionic mixtureDES is synthesized by heating up the mixture of two individual

solids which are choline chloride and urea in the ratio of 1:2 undermanual stirring conditions using a hot plate. Upon synthesis, thesolid form chemicals will completely dissolve and appear as a color-less viscous solution.

2.2.2. Sample preparationThe initial step in developing CS based polymer electrolytes is by

dissolving an appropriate amount of CS powder as shown in Table 1in 15 ml of distilled water and heat the milky solution till the temper-ature of 75 C in order to gelatinize the CS. This step yields a transpar-ent viscous solution. After the heating process, the solution wascooled at ambient temperature under constant stirring for about30 min. Then an appropriate content of LiTFSI and the synthesizedDES were added into the viscous solution and again the solutionwas allowed to stir for another hour to allow a good miscibility be-tween the added chemical constituents. The polymer electrolyteswere then cast on a clean Teon plate and dried in the oven at 55 Cfor 8 h. This procedure yields sample in two different forms, mechan-ically free standing thin lm for sample DES-0 and samples withlower DES content (DES-20 and DES-40) and consequently formsgel-like samples at higher plasticization (DES-60 and DES-80).

Table 1Composition ratio of CS:LiTFSI:DES system with the ionic conductivity, relaxation fre-quency and activation energy (Ea) exhibited by polymer electrolytes with differentDES content.

Sample Polymerelectrolyte (CS:LiTFSI:DES) (wt.%)

Ionicconductivity at50 C, (S cm1)

Relaxationfrequency, log[m (Hz)]

Activationenergy, Ea(kJ mol1)

DES-0 70: 30:0 2.26105 DES-20 56: 24:20 4.98105 4.70 13.16DES-40 49: 21:40 7.56105 5.10 12.55DES-60 28: 12:60 9.09104 6.00 8.25DES-80 14: 6:80 4.56103 6.03 8.22Please cite this article as: S. Ramesh, et al., J. Mol. Liq. (2011), doi:10.10ED P

ROOFuminium crucible. The sample was heated sequentially from 25 C to500 C at the heating rate of 10 C min1 under an inert environment

with the nitrogen ow rate of ca. 50 ml min1.

2.3.3. TGA analysisThe thermal properties of polymer electrolytes were obtained by

using the Mettler Toledo analyzer consisting of TGA/SDTA851e mainunit and STARe software. This analysis was carried out at the tempera-ture ranging from 25 C to 550 C with the heating rate of 10 C min1

under nitrogen atmosphere.

3. Results and discussion

3.1. Temperature dependent conductivity studies

Fig. 1 shows the variation of log ionic conductivity as a function ofreciprocal temperature for plasticized polymer electrolytes with theDES content of 20, 40, 60 and 80 wt.%. The regression values (R2) thatlie close to unity reveal the linear relationship that co-exists betweenthese two parameters. It can be veried that all the tested samplesobey Arrhenius theory revealing that the conductivity mechanism isthermally assisted [14]. The nature of cation transport in the DES plasti-cized samples is quite similar to that in ionic crystals, wheremobile ionsjump into neighbouring vacant sites [15].

This model explains that when the temperature of polymer elec-trolytes is increased, the mobile cations acquire high energy allowingfrequent inter or intra-chain ion hopping and accordingly the ionicconductivity of the polymer electrolyte will be improved with risein temperature from 50 C to 100 C.

All the tested samples obey Arrhenius theory revealing that thereis no phase transition in the plasticized polymer electrolyte matrix inthe temperature range studied. The ion transport mechanism in poly-mer electrolytes can effectively be expressed as below:

oexp Ea=KT 4:1

Fig. 1. Arrhenius plots of log conductivity against reciprocal temperature for sample

DES-20 (), DES-40 (), DES-60 () and DES-80 (x).

16/j.molliq.2011.11.010

T172173 where o is a pre-exponential factor, Ea is the activation energy and T174 is the absolute temperature in K.175 Table 1 summarizes the activation energy (Ea) of polymer electro-176 lytes with different DES content calculated from the slope of the Ar-177 rhenius plot. Based on the tabulated results, it was found that Ea178 decreases with increase in DES content. This was attributed to the in-179 crease in the amorphous elastomeric fraction in the CS:LiTFSI:DES180 matrix that facilitates fast Li+ ion motion in polymer network upon181 increase in temperature [15,16]. The sample with lowest Ea value182 will exhibit the highest ionic conductivity due to greater migration183 of Li+ ions.

184 3.2. Frequency dependence of loss tangent studies

185 Figs. 2 and 3 shed some light on the ionic transport mechanism in186 CS matrix when different concentration of DES is incorporated in CS:187

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251Knowledge on the inuence of both LiTFSI and DES content on the252CS matrix thermal properties was evaluated by the overlay thermo-253gravimetric curves of pure CS, DES-0, DES-20 and DES-80 as

Table 2 t2:1The melting temperature, maximum decomposition temperature and total weight lossof pure CS, DES-0, DES-20 and DES-80.

t2:2t2:3Sample Temperature, T (C) Total

weightloss,wt (%)

t2:4Melting, Tm Maximum decomposition, Td

t2:5Pure CS 313.36 317.56 86t2:6DES-0 291.12 406.67 82t2:7DES-20 257.57 382.50 80t2:8DES-80 236.69 261.45 88

3S. Ramesh et al. / Journal of Molecular Liquids xxx (2011) xxxxxxUNCORREC

LiTFSI:DES system. From Fig. 2 it can be observed that the loss tangentpeaks were found to have shifted towards the higher frequency uponincrease in DES content similar to sample DES-80 in Fig. 3. The in-crease in the relaxation frequency (logmax ) as a function of DEScontent is summarized in Table 1. The observation illustrates the re-duction in the relaxation time of Li+ ions due to greater accelerationon its mobility with increase in DES content [17]. As more DES is in-corporated into the CS:LiTFSI:DES matrix, more amorphous regionwill be available and facilitates the mobility of Li+ ions in the matrix.Hence, enhancement in the ionic conductivity is observed.

Other plausible reasons for the displacement of loss tangent peaksto higher frequency may be correlated to the increase in the numberof non-bridging ions in DES (Cl) that act as a transit site for the mo-bility of Li+ ions. This transit site shortens the distance for Li+ ions tohop from one oxygen atom to another in polymer chain acquiring lessenergy loss for the mobility of ion. Hence, frequent migrations of mo-bile ions are expected to occur which is crucial in enhancing the ionicconductivity.

The magnitude of tan also provides an informative insight on thenumber of Li+ ions that participate in ion conduction [18]. The in-crease in the magnitude of tan upon increase in DES content in-ferred to the increase in the area under the loss factor peak. Thiswas ascribed to the increase in the number of Li+ ions that partici-pates in the relaxation process to assist the ionic conductivity. The in-crease in Li+ ion concentration evidences the efciency of DES inovercoming the Coulombic force in LiTFSI, making more Li+ ions tobe available in enhancing the ionic conductivity. Sample DES-80 ex-hibits the highest magnitude of tan compared to the rest of the test-ed samples attributed to the greater presence of Li+ ions.

The increase in DES content in polymer electrolyte increases theconcentration of mobile Li+ ions that participate in ion conductionwhile speeding up its mobility as it improves in the amorphous elas-tomeric phase. Thus, increase in ionic conductivity will be observed as

Fig. 2. Variation of tan with frequency for samples DES-20 (), DES-40 () and DES-

60 () at room temperature.

Please cite this article as: S. Ramesh, et al., J. Mol. Liq. (2011), doi:10.10ED P

ROOF

increasing plasticization of DES. Sample DES-80 obtained the highestionic conductivity owing to the presence of high concentration of mo-bile Li+ ions coupled with greater mobility.

3.3. Differential scanning calorimetry (DSC)

The melting temperature of pure CS, DES-0, DES-20 and DES-80was summarized in Table 2 and the exhibited variation provides aninsight on the constituent's miscibility which inuences the structuralproperties. It was observed that the melting temperature decreaseswith addition of LiTFSI and further declines with increase in DEScontent.

The reduction in the melting temperature of DES-0 compared topure CS reveals the possible interaction between CS and LiTFSI [19].The outcome of this interaction persuades a disruption in the avail-able crystalline fraction which increases the amorphocity of polymerelectrolytes and allows the matrix to melt at lower temperature.

Further decrease in melting temperature was observed upon in-corporation of 20 wt.% DES in polymer electrolytes. This nding is ev-idence of the miscibility of DES in CS:LiTFSI matrix. The observeddecline in melting temperature was attributed to the enhancementin structural disorderness results of the complexation, which in-creases the fraction of amorphous region. The atoms present in theamorphous region are weakly bonded, thus a small amount of heatis sufcient to overcome the weak bonding in order to melt the amor-phous natured polymer matrix. Hence, a reduction in the meltingtemperature will be observed as more DES content is incorporatedin the polymer electrolytes.

In view of the results, it can be noted that the melting temperatureof polymer electrolytes are reduced as more DES content is incorpo-rated. This veries the complete miscibility of DES in CS:LiTFSI matrixwhich induces structural disorderliness.

Fig. 3. Variation of tan with frequency for sample DES-80 at room temperature.16/j.molliq.2011.11.010

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294which easily decomposes at lower temperature. Nevertheless this ef-295fort improves the thermal stability of the polymer electrolytes evi-296dent by the lesser total weight loss.297Further increase in DES content leads to the decline in both the298heat-resistivity and thermal stability. This was associated to the pres-299ence of greater amorphous phase in the polymer electrolytes making300it more heat sensitive. Thus, reduction in heat-resistivity will be ob-301served companied by the increment in total weight loss as more302

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represented in Fig. 4. The maximum decomposition temperature andtotal weight loss being obtained from Fig. 4 have been recapitulatedin Table 2.

Based on the thermogravimetric curve of DES-0, an improvementin both the heat-resistivity and thermal stability of pure CS was ob-served upon incorporation of LiTFSI. The observed enhancement inheat-resistivity was correlated to the decomposition of the organicpart in LiTFSI which induces the displacement of the maximum de-composition temperature to a higher level. Since it is heat stable,less monomer will be detached from the complex structure, hencelowering the total weight loss.

Thermal properties are further altered upon addition of DES inpolymer electrolytes. It can be observed that the DES plasticized poly-mer electrolytes exhibited weight loss starting at temperature 100 C,which was almost 200 C lower than those experienced by non-plasticized sample as in Fig. 4.8. These reveal that the crystallinestructures of the plasticized samples were not sustained due to thegood miscibility of DES in CS:LiTFSI matrix.

The displacement of the maximum decomposition temperature ofsample DES-20 to lower temperature reveals the decline in the sam-ples heat-resistivity. The diminishing heat-resistivity explains thepossible structural disorderness in CS matrix that leads to the exis-tence of high amorphous fraction, having atoms that poorly coordi-nated. Apparently, small amount of heat is sufcient to overcomethe weak interactions between the connected atoms and hencedecomposed at lower temperature. This incorporation improves thethermal stability of the polymer electrolytes which is evidenced bythe reduction in total weight loss.

Further increase in DES content leads to the decline in both theheat-resistivity and thermal stability. This was associated with thepresence of greater amorphous phase in the polymer electrolytesmaking it more heat sensitive. Hence, reduction in heat-resistivity

Fig. 4. Thermogravimetric curves for pure CS (), DES-0 (), DES-20 () and DES-80 (x).UNC

will be observed companied by an increase in total weight loss asmore DES particles are decomposed from the polymer electrolyte ma-trix upon the heating process [20].

With reference to sample DES-20, the displacement of the maxi-mum decomposition temperature to lower temperature reveals thedecline in the samples heat-resistivity. The diminishing in heat-resistivity reasonably explains the possible structural disordernessin CS matrix that leads to the existence of high amorphous fraction

343344345346347348349350351352353

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ROOF

DES particles being eliminated out from the polymer electrolytes ma-trix upon the heating process [20].

4. Conclusion

High conducting green polymer electrolytes were synthesized byplasticizing the CS:LiTFSI matrix with DES. Conductivitytemperatureplot reveals the cation transport mechanism that obeys Arrheniusrule. The maximum enhancement in the ionic conductivity wasachieved upon incorporating with 80 wt.% of DES in CS:LiTFSI matrixwith the value 4.56103 S cm1 at 50 C and activation energy of8.22 kJ mol1. The continuous displacements of tan peak at higherfrequency upon the increase in DES content suggest the increase inthe ionic transport mechanism. Sample DES-80 exhibits the highestrelaxation frequency with the value of log m=6.03 indicating itslow relaxation time. The melting temperature of polymer electrolytesdecreases with the increase in DES content due to the occurrence ofcomplexation that suppresses the crystalline phase. TGA analysis re-veals that the incorporation of DES in the polymer electrolytes signif-icantly diminishes the heat-resistivity but an enhancement in thethermal stability occurs upon the minimum addition of DES.

References

[1] D.F. Vieira, C.O. Avellaneda, A. Pawlicka, Electrochim. Acta 53 (2007) 14041408.[2] R.L. Wu, X.L. Wang, F. Li, H.Z. Li, Y.Z. Wang, Bioresour. Technol. 100 (2009)

25692574.[3] Y.X. Xu, V. Miladinov, M.A. Hanna, Cereal Chem. 81 (2004) 735740.[4] C. Beninca, I.M. Demiate, L.G. Lacerda, M.A.S. Carvalho Filho, M. Ionashiro, E.

Schnitzler, Ecletica Quim. 33 (2008) 1318.[5] Y. Takeda, S. Tomooka, S. Hizukuri, Carbohydr. Res. 246 (1993) 267272.[6] W. Ning, Z. Xingxiang, L. Haihui, H. Benqiao, Carbohydr. Polym. 76 (2009)

482484.[7] W.A. Atwell, L.F. Hood, D.R. Lineback, E. Varriano-Marston, H.F. Zobel, Cereal Food

Worlds 33 (1988) 306311.[8] A.P. Abbott, G. Capper, D.L. Davies, R.K. Rasheed, V. Tambyrajah, Chem. Commun.

39 (2003) 7071.[9] Y. Hou, Y. Gu, S. Zhang, F. Yang, H. Ding, Y. Shan, J. Mol. Liq. 143 (2008) 154159.

[10] H.R. Jhong, D.S.H. Wong, C.C. Wan, Y.Y. Wang, T.C. Wei, Electrochem. Commun. 11(2009) 209211.

[11] J. Zhang, T. Wu, S. Chen, P. Feng, X. Bu, Angew. Chem. Int. Ed. Engl. 48 (2009)34863490.

[12] S. Rajendran, M. Sivakumar, R. Subadevi, Mater. Lett. 58 (2004) 641649.[13] J. Siva Kumar, A.R. Subrahmanyam, M. Jaipal Reddy, U.V. Subba Rao, Mater. Lett.

60 (2006) 33463349.[14] D.F. Shriver, B.L. Papke, M.A. Ratner, R. Dupon, T. Wong, M. Brodwin, Solid State

Ionics 5 (1981) 8388.[15] M.B. Armand, Annu. Rev. Mater. Sci. 16 (1986) 245261.[16] M.A. Ratner, D.F. Shriver, Chem. Rev. 88 (1988) 109124.[17] D.K. Paradhan, R.N.P. Choundhary, B.K. Samantaray, Int. J. Electrochem. Sci. 3

(2008) 597608.[18] M.A.S. Azizi Samir, F. Alloin, W. Gorecki, J.Y. Sanchez, A. Dufresne, J. Phys. Chem. B

108 (2004) 1084510852.[19] M.Z. Norashikin, M.Z. Ibrahim, World Acad. Sci. Eng. Technol. 58 (2009) 176180.[20] A.A. Mohamad, A.K. Arof, Mater. Lett. 61 (2007) 30963099.16/j.molliq.2011.11.010

Exerted influence of deep eutectic solvent concentration in the room temperature ionic conductivity and thermal behavior of...1. Introduction2. Experimental2.1. Materials2.2. Preparation of polymer electrolytes2.2.1. Synthesizing ionic mixture2.2.2. Sample preparation

2.3. Instrumentation2.3.1. Impedance spectroscopy2.3.2. DSC analysis2.3.3. TGA analysis

3. Results and discussion3.1. Temperature dependent conductivity studies3.2. Frequency dependence of loss tangent studies3.3. Differential scanning calorimetry (DSC)3.4. Thermogravimetric analysis

4. ConclusionReferences