NATIONAL WORKSHOP ON FUNCTIONAL MATERIALS 2009

Characterization And Ionic Conductivity Of PolymericElectrolytes Based On Chitosan-Ammonium Thiocyanate- TiOz

Ceramic Materials

N.A. Aziz, S.R. Majid and A.K. Arof*

Center for Ionics University of Malaya, Faculty of Science, University of Malaya,50603 Kuala Lumpur, Malaysia

*Coressponding author: akarof@um.edu.my

Abstract

"' arious amounts of Ti02 particles are used as filler in preparation of chitosan-ammonifthiocyanate-composite polymer electrolytes. The role of filler in this present work is as 8agent to improve the conductivity of the films. Films of chitosan and its complexes w~prepared using solution casting technique. Different amounts of Ti02 3 wt. %, 6 wt. %, 9 ~ofo; 12 wt. %, 15 wt. % and 18 wt. % were added to the highest room temperature conducti'sample in chitosan-salt system i.e sample containing 40 wt. % NH4SCN. The impedance (the composite films has been measured in the temperature and the frequency range 298 J{ I373 K and 50 Hz to 1 MHz, respectively. The conductivity value of this sample is 1.29 x IJScm-I. With addition of 3 wt. % Ti02 filler the ionic conductivity increased to 2.75 x 10em". XRD and FTIR results are also disscused.

Keywords: ionic conductivity, ceramic fillers, polymer-nanocomposite, chitosan

1. INTRODUCTION

Solid polymer electrolytes have been thesubject of numerous studies. Theirtechnological importance can be seen in thefabrication of lithium-ion polymer batteries[1], capacitors [2], and electro chromicdevices [3]. Most research on electrolytesfocu ed on increasing their conductivitywhile at the same time maintains goodthermal and mechanical stability. Theaddition of inert oxides to the polymerelectrolytes has recently become anattractive approach, due to improvedmechanical stability and enhanced ionicconductivity [4-6]. The increase inconductivitfy of the composite electrolytesdepends upon the concentration and thesizes particle fillers. In general, the smallerthe inert particle, the larger the conductivityenhancement [7-8].

The disadvantage of organic fillers uch apropylene carbonate (PC) and ethylene

carbonate (EC) is that they are JIlOI

expensive compared with inorganic fiilel[9]. Fillers can promote more free ions aJlproduce more amorphous regions in ~

'1electrolyte for transport of charge carrIe[10].

In this work chitosan-N~SCN-rj(composite polymer electrolyte has b~developed, in which the titanium diox'(Ti02) as the filler has increase ~conductivity. The effects of Ti02 ....~chitosan-Nlla'X'N are also studied by XlVFTIR and SEM.

2. EXPERIMENTAL

2.1 Materials and Preparation

Chitosan (highly viscous) was procotlfrom Fluka as the polymer host. Acetic. a:was procured from Univar ChernivAmmonium thiocyanate (R&M) was used j

NATIONAL WORKSHOP ON FUNCTIONAL MATERIALS 2009

the doping salt and Ti02 (titanium (IV)oxide) from Aldrich was used as filler.

The chitosan was dissolved in 1 % aceticacid and the mixture was stirred at roomtemperature for 3 h to obtain a homogeneoussolution. 40 wt. % of ammoniumthiocyanate was added to the solution andstirred until the salt has dissolvedcompletely. Ti02 was added accordingly atthe required concentrations. Thehomogenous solution was then cast intoseveral plastic petri dishes to get the films.

2.2 Characterizations

2.2.1 Conductivity Measurements.

The dried films were cut into a suitablesize and mounted on the conductivityholder with stainless steel electrodes of 1em diameter under spring pressure. Theimpedance of all samples was measuredusing the HIOKI 3531-01 LCR Hi-Testerinterfaced to a computer with frequencyranging from 50 Hz to 1 MHz and also attemperatures from 298 K to 393 K. Theelectrical conductivity was then calculatedusing the equation:

(1)

Here t is thickness of the sample, A isthe surface area of contact and Rb is thebulk resistance of the sample.

2.2.2 X-Ray Diffractometer (XRD)

X-ray diffraction was performed usingShimadzu D5000 to examine the crystallinenature of the prepared polymer compositesamples.

2.2.3 Fourier TransformSpectroscopy (FTlR)

Infrared

The FTIR spectroscopy patterns wererecorded using Thermo Scientific/Ni coletis 10. Infrared absorption spectra werecollected in the range from 4000 to 400 cm-I

at room temperature with a resolution of 1-Icm .

3. RESULTS AND DISCUSSION

Fig. 1 shows the XRD patterns of someprepared samples obtained at roomtemperature.

l j ..&. ; . ~.,.~;);I

,

5 15 25 35 45 55 65 75

5 0 fi ~ ~ ~ ~ ~ ~ ~ ~ ro ~ n D ~29 (degree)

Fig. 1 Diffractograms of films for (a) pure chitosanacetate, (b) chitosan acetate-40 wt. % NH4SCN,(c) chitosan acetate - 40 wt. % NH4SCN - 3 wt. %Ti02, (d) chitosan acetate-40 wt. % NH4SCN - 6wt. % Ti02, (e) chitosan acetate-40 wt. % NH4SCN-9 wt.% Ti02, (f) chitosan acetate-40 wt. % NH4SCN- 12 wt. % Ti02, (g) chitosan acetate-40 wt. %NH4SCN - 15 wt.% Ti02, (h) chitosan acetate - 40wt. % NH4SCN - 18 wt.% Ti02 and (i) pure Ti02.

The XRD pattern of pure chitosan showstwo halos at 28=15.5° and 2l.6°. It wasreported that pure chitosan film exhibitpeaks at 28 angles of 21 0, between 16° to24° and 29° [11]. When 40 wt. % TH4SCNwas added to pure chitosan acetate theintensity of both peaks has decreased andgives a completely amorphous film. Thebroad peaks indicate that the films areamorphous [12]. The conductivity willmcrease when the material becomes morea~orphous or less crystalline. Based on thediffractograms, the sample with 3 wt. % of

76

NATIONAL WORKSHOP ON FUNCTIONAL MATERIALS 2009

filler exhibits the most amorphousdiffractogram. Thus it may have higherconductivity compared to the other samples.Fig. 2 shows the effect of filler on theconductivity of chitosan-NH4SCN-Ti02system at room temperature.

-35

-3.55~--3.6SCJ

00-3.65'-'

b..........

:.3.7.;;:::CJ= -75'Qc0CJ -3.8ell0..:l

-3.85

-39

CPIo 3% (flo 9110 ]2>10 15% 1811oFiller contents (wt. %)

Fig. 2 Room temperature conductivity of polymercomposite samples with different filler content.

The polymeric composite shows maximumin conductivity at 3 wt. % of Ti02• Theconductivity value is 2.75 x 10-4 Scm-I. Atthis filler content, the addition of filler mayhave created additional pathways for the ionto transport and could have also resulted in agreater number of mobile ions due todissociation of the salt. [13-14]. Theconductivity decreases for the samplecontaining 6 wt. %, 9 wt. %, 12 wt. %, 15wt. % and 18 wt. %. This results are in goodagreement with the XRD results where thecrystallinity of the samples have increasedwith increasing amount of filler thusdecreasing the conductivity. Thecond ctivity (a)-temperature (1) plots of thechitosan based electrolyte is shown in Fig. 3.

-1.8

(a)-2.0--'s

~-2.2'-'bello..:l-2.4

-2.6 -

-2.8-6.2 -5.7 . -5.2 -4.7 _4.;

1000/T (Iel)

-0.7

• (b)• •-0.8 • • •«: •sCJ -0.9 •00 •'-'b •ell •0 -I..:l •

•·1.1 •

-1.2 '-------------

2.65 2.85 3.05 3.2510001 T(IeI)

Fig. 3 Arrhenius plot of conductivity for (a) chit09acetate-40 wt. % NH4SCN and (b) chitosan ace~40 wt. % NH4SCN-3 wt.% Ti02•

The plot shows that as the temperat~increases, the conductivity also increaS'

'INg and Mohamed [15] have al 0 obse~the same trend. The conductivftemp rature relationship of chitosan-b~polymer electrolyte can b characterized:Arrhenius behavior ugge ting tilconductivity i thermally table. ~acti ation nerg, Ea of the ampl call.cal ulat d u ing the m difi d rrheot!quati n b I w:

NATIONAL WORKSHOP ON FUNCTIONAL MATERIALS 2009

Here T is the experimental temperature inKelvin, (J is conductivity, (Jo is pre-exponential factor, Ea is the activationenergy and Ks is the Boltzmann constant.From the slope of the graph in Fig. 3, thecalculated activation energy for conductionis 0.19 eV and 0.08 eV for salted andcomposite samples, respectively. Thedecrease in activation energy is consistentwith an increase in conductivity as reportedin many reports on conductivity studies ofpolymer electrolytes [16-17].

The increase in ion dissociation andreduction of ion pairing in the electrolytecan be discussed further based on the FTIRspectrum as shown in Fig. 4.

It}11409 l'I 1146

III

2045

/ (b)

(a)

1144

II I 1513 J '\)612~1:,t 1050 1024

2200 1700 1200 700W~v~nllmh~r

Fig. 4 IR spectrum of film containing (a) chitosanacetate, (b) chitosan acetate-NH4SCN and(c) chitosan acetate-NH4SCN-Ti02 in the region from700to 2300em"

Fig. 4 depicts the spectra of pure chitosan,chitosan acetate with salt and chitosanacetate with salt and filler. The carbonyl(C=O-NHR), amine (NH2) and ammonium(NH3+) bands are situated in the region

between 1400 and 1700 em-I.From the literature, the C=O-NHR band canbe observed at 1650 em" [18], the amineNH2 band is at 1590 em-I and theammonium NH3+ band at 1514 em-I [19].Sometimes, the absence of the NH3+ purechitosan acetate spectrum is probably due tothe interaction between NH3+of the chitosanand the -COO- of the acetic acid solvent toform the O=C-NHR band [20].

In this work, the carbonyl band of thechitosan acetate spectrum can be observed at1634 em-I and the amine band at 1544 em-I.The carbonyl band has shift to lowerwavelength at 1612 em-I and the amine bandat 1513 em". The shift in the chitosan-salispectrum indicates some interactions haveoccurred between the salt and the nitrogendonors of the chitosan. SCN- belongs tcpoint group symmetry and has threevibrational modes associated with C1\stretching, CS stretching and doublydegenerate SCN bending, respectively. C1\stretching in most PEO-based polymeielectrolytes appears as one envelope in theregion between 2150 and 2000 em" [21-22]

In this work CN stretching can be observecat 2043 em-I in the spectrum of chitosarwith salt and shift to 2045 em-I in tluspectrum of chitosan with salt and filler. Tluintensity of this band also increases due t(the addition of filler. The polymer-salcomplex formation and the protoiinteraction have been confirmed from thabove analysis.

4. CONCLUSIONS

It can be inferred that the presence of thceramic filler can help to improve thconductivity of the prepared samples. XRland FTIR results clearly showed interactiobetween Ti02 filler and the completelamorphous chitosan-based polymeelectrolyte. The conductivity value of tl:order ~10-4S ern" that has been obtained badding the Ti02 filler to chitosan-sapolymer electrolyte can make thcomp?site polymer electrolyte as a potentimatenal for some electrochemical devices.

78

ACKNOWLEDGEMENT

NA T10NAL WORKSHOP ON FUNCTIONAL MA TERIALS 2009

The author would like to thank theUniversity of Malaya for the UniversityMalaya Research Grant (UMRG) awarded(RG06509AFC).

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