Structure, interaction and thermal study in electrolyte of polyethylene oxide/silica/ammonium...

Structure, Interaction and Thermal Study in Electrolyteof Polyethylene Oxide/Silica/Ammonium ThiocynateNanocomposites

Kamlesh Pandey,1 Mrigank Mauli Dwivedi,1 Mridula Tripathi21National Centre of Experimental Mineralogy and Petrology, University of Allahabad, Allahabad-211 002, India

2C.M.P. Degree College, University of Allahabad, Allahabad-211 002, India

Composite polymer electrolyte consisting of polymer(polyethylene oxide, PEO) and nanosized ceramic fillerwith different concentrations of salt have been synthe-sized and characterized. X-ray diffraction analysisshows that polymer salt complex has been intercalatedinto the naometric silicate layers. IR spectra reveal thatthe polymer structure in the ceramic interlayer is simi-lar to that of polymer salt complexes and there is astrong interaction between PEO:SiO2 and polymer-saltcomplexes. POLYM. COMPOS., 30:503–509, 2009. ª 2008Society of Plastics Engineers

INTRODUCTION

The rapid growth of portable electronic devices (like

3C i.e. computer, camcorders, and cellular phones [1])

and electric/hybrid vehicles have increased the demand of

compact light weight, high capacity solid state recharge-

able batteries. The polymer electrolytes have recently

became a hot contender because of their significant theo-

retical interest as well as practical importance for the

development of solid state electrochemical devices [2–5].

Wright [6], for the first time explored the complexation of

PEO with alkali salts. The polyethylene oxide (PEO) is a

semicrystalline polymer at room temperature and has an

exceptional property to dissolve with high concentration

of a wide variety of dopants [7]. In PEO, the solvation of

salts occurs through the association of metallic cations

with the oxygen atom in the back bone. The multiphase

nature of the PEO is most often regarded as a major prob-

lem in the working of systems. Various attempts have

been made to modify the structure of the polymer electro-

lyte in order to improve their electrical, electrochemical,

and mechanical properties. In this direction, the formation

of composite polymer electrolyte (CPEs) introduced a

new class of polymer electrolyte in which an inorganic/

ceramic filler [8–10] or high molecular weight organic fil-

ler [11] is dispersed in to polymer electrolyte as a third

component. This seems to be a better approach [12, 13].

The dispersion of ceramic filler in polymer electrolyte to

improve their mechanical strength was first suggested by

Weston and Steele [14]. Since then number of inorganic/

ceramic and organic additives have been reported [15, 16].

In the present communication, we report a new PEO-

based polymeric electrolyte with silica as ceramic filler

and ammonium thiocynate as salt. The effect of additive

filler and salt on the structural and thermal property of

solid polymer electrolyte was investigated by differential

scanning calorimetry (DSC), X-ray diffraction (XRD), op-

tical micrography, SEM, and IR spectroscopy.

EXPERIMENTAL

CPE films were prepared by the solution cast tech-

nique. For the synthesis of electrolyte film, polyethylene

oxide (PEO, MW ¼ 6 3 105, ACROS organics) was used

as the polymer host matrix. Ammonium thiocynate

(NH4SCN, AR grade, Rankem India) as salt and the

nano-sized SiO2 as ceramic filler were mixed in the poly-

mer. The ceramic filler SiO2 was prepared by standard

sol-gel technique. For gel preparation, tetraethyl orthosili-

cate (TEOS, Aldrich) was used as precursor, ethanol as

solvent and ammonia solution (basic medium pH � 10) as

a catalyst. The hydrolysis of TEOS was completed in two

steps [17]. The gel solution was divided in two parts

(solution-1 and solution-2). Solution-1 was gellified at

408C (gellification started after 48 h) and dried at 2008C.Refractive index (R.I.) of this dried powder was measured

(R.I. ¼ 1.426) by Index Matching technique. The appro-

priate amount of the PEO was dissolved in deionized (DI)

water at 408C and then solution-2 was mixed in it. This

solution was stirred vigorously for 12 h. For the addition

of salt, we used 2–20 wt% of vacuum dried NH4SCN.

Correspondence to: Kamlesh Pandey; e-mail: [email protected]

DOI 10.1002/pc.20625

Published online in Wiley InterScience (www.interscience.wiley.com).

VVC 2008 Society of Plastics Engineers

POLYMER COMPOSITES—-2009

This gelatinous polymer solution was cast in a polypro-

pylene petri dish. The solution casted film was dried at

room temperature followed by a vacuum drying. Finally,

we obtained solvent free thin CPE film. It was observed

that maximum limit of SiO2 is 35% for film formation.

When we increased the SiO2 ratio beyond 35%, either a

brittle film or fine powder was obtained. Similar observa-

tions were also recorded with increasing concentration of

salt. This effect is possibly due to modification/increase

of Tg2 of the polymer composite electrolyte with the

increase in filler/salt concentration.

The X-ray pattern of films was recorded at room tem-

perature using Phillips X-Pert diffractometer with Cu Ka

radiation (k ¼ 1.5405 A) in a wide 2h (Bragg angle) val-

ues 158 \ 2h \ 608. The Infrared spectrum was recorded

by Perkin Elmer IR spectrophotometer from 4,000 to 400

cm21 wavenumbers. The DSC data was collected with a

DuPont 1090 thermal analyzer. DSC analysis was per-

formed on 2–4 mg sample between 27 and 1508C temper-

atures at the heating rate of 58C/min under N2 atmos-

phere. The optical micrograph and SEM image of the

polymeric films were taken by the computer controlled

Leica DMLP polarizing microscope and Jeol JXA 8100

EPMA, respectively.

RESULT AND DISCUSSION

X-Ray Diffraction Study

The XRD pattern of pure PEO film shows sharp and

intense peaks at 2h values of 198 and 238. Existence of

broad peaks in addition to few sharp reflections, confirm

its partially crystalline and partially amorphous nature.

The unit cell of the PEO is (O��CH2��CH2) and the

bond length is of the order of 19.2 A [18]. To overcome

the problem of partially crystalline and partially amor-

phous structure, ceramic filler/and salt were doped in

PEO host matrix. The intercalation of polymer chain with

silica, usually increases the interlayer spacing of ceramic

material. This effect leads to shift of diffraction peaks

towards the lower values of angles which are related

through the Bragg’s relation

k ¼ 2d sin h (1)

The XRD patterns of (1 2 x)PEO:x SiO2 and [PEO:

SiO2]:NH4SCN are shown in Fig. 1a and b, respectively.

From the Fig. 1a, it is clear that the addition of SiO2 in

PEO reduces the intensity of main peaks (in PEO, 2h ¼198 and 238) followed by broadening of the peak area,

which is an indication of reduction in degree of crystallin-

ity. Beyond 50 wt% of SiO2, the peaks are suppressed

due to broadening and some new peaks of SiO2 appear.

These diffractograms also indicate that, at lower SiO2

content, the crystallite size of silica is large but as SiO2

concentration is increased, the dispersal becomes homoge-

neous followed by reduction in size. At higher concentra-

tion of SiO2 due to the cluster formation, the SiO2 peak

reappears and the crystallinity decreases i.e. amorphousity

increases. Moreover, due to addition of silica diffraction

FIG. 1. (a) XRD pattern of xPEO þ (1 2 x) SiO2 (x in wt%), (b) XRD

Pattern of 95[xPEO þ (1 2 x) SiO2] þ 5 NH4SCN.

504 POLYMER COMPOSITES—-2009 DOI 10.1002/pc

maxima shift towards to lower values of 2h. The magni-

tude of the shift varies with doping concentration. After

doping of salt i.e., NH4SCN (5–10 wt%) in polymer ce-

ramic composite, it was observed that no new

peaks appear but the existing peak of PEO:SiO2 reap-

pear with reduced intensity (Fig. 1b). The higher doping

concentration of salt (\20 wt%) gives a completely

amorphous film. This indicates that the degree of crys-

TABLE 1. Average particle size of PEO:SiO2 for different composition.

S. No. Sample composition Average particle size (nm)

1 Pure PEO film 45.2

2 90 wt% PEO þ 10 wt% SiO2 film 23.7



5 60 wt% PEO þ 40 wt% SIO2 film 21.2

6 20 wt% PEO þ 80 wt% SiO2 powder 31.8

7 [90 wt% PEO þ 10 wt% SiO2]95:(NH4SCN)5 film 32.5

8 [80 wt% PEO þ 20 wt% SiO2]95:(NH4SCN)5 film 25.7

9 SiO2 powder 50–60

FIG. 2. Optical micrographs of (a) PEO, (b) 90 PEO þ 10 SiO2, (c) 70 PEO þ 30 SiO2 and (d) 95 [90

PEO þ 10 SiO2] þ 5 NH4SCN.

DOI 10.1002/pc POLYMER COMPOSITES—-2009 505

tallinity also decreases with the increase in salt content.

The average crystallite sizes in polymeric films as

calculated by the Scherrer formula [19] are summarized

in Table 1. The average particle size varies from 30 to

70 nm.

SEM and Optical Study

The optical micrographs of pure PEO, PEO:SiO2, and

PEO-SiO2:NH4SCN are shown in Fig. 2. Distinct spheru-

lites are visualized in the pure PEO film, which indicates

the lamellar microstructure of pure polymer (Fig. 2a). The

dark boundaries observed between the spherulites show

the partial amorphous phase of the film. The morphology

of the film changes substantially on addition of SiO2,

which can be observed in Fig. 2b and c. This also

shows the heterogeneous dispersion in lower percentage

of ceramic additive but in higher side it became more

homogeneous.

Figure 3 shows the SEM micrographs of the PEO-SiO2

and PEO-SiO2:NH4SCN complexes. The micrographs of

the PEO-SiO2 complexes indicate the presence of spheru-

lites that shows characteristic lamellar microstructure. The

boundary between the spherulite shows the existence of

amorphous phase. Crystalline part was able to form due

to longer evaporation time. The size of the spherulite

structure decreases on the addition of ceramic filler, and it

becomes distinct with increase in the boundary region. On

further increase of SiO2 content the number of white spots

increase, which indicates that the particles are homogene-

ously distributed in the matrix and disturb the original na-

ture of the matrix. Similarly, addition of salt in PEO:SiO2

gives the similar structure with separate entity. In these

films, the size of the particulates is of nanometer order.

FIG. 3. SEM image of the (a) PEO, (b) and (c) xPEO þ (1 2 x) SiO2 (x in wt%) and (d) 95 [xPEO þ (1 2 x)

SiO2]þ 5 NH4SCN.


This result supports the calculated particle size as

obtained by the XRD experiments.

Infrared Spectroscopic Study

Infrared spectroscopy is a powerful tool for character-

izing the organic–inorganic and composite materials.

Figure 4 shows the IR spectra of PEO:SiO2 and/with

NH4SCN salt. The peak assignments of these spectra are

given in Table 2. In PEO:SiO2 film the broad peaks at

3,700 and 1,620 cm21 are due to ��OH stretching and

��OH bending, the peaks at 3,000–3,100, 1,700, 1,410,

1,390 cm21 are related to C��H stretching, C��H in

plane bending, C��O stretching and m CH2��O, respec-

tively. The other silica related peaks are found at 941 and

802 cm21. In pure PEO a triplet peak [21] is expected at

1,149, 1,109, 1,061 cm, and 1,280 cm21 related to

��C��H twisting. But after the addition of SiO2 these

peaks disappear. This is an indication of reduction in

degree of crystallinity. Some new peaks at 2,000–

2,100 cm21 were observed after the doping of salt. These

peaks are related to formation of crystalline complex

of x(PEO:SiO2):(1 2 x)NH4SCN. The intensity of peaks

1,343 and 1,360 cm21 (CH2 wagging modes) decrease

drastically and a new sharp band at 1,350 cm21 appears

after the doping of NH4SCN. This effect is related to the

FIG. 4. Infrared spectra of (a) 90 PEO þ 10 SiO2 and (b) 95 [90 PEO þ 10 SiO2] þ 5 NH4SCN (PEO

spectrum in inset [20]).

TABLE 2. Assignment of different IR peaks of PEO:SiO2 and [PEO:SiO2]:NH4SCN.

Peak position in PEO:SiO2 Peak position in x(PEO:SiO2):(1 2 x)NH4SCN Assignments

Broad peak at 3,650–3,800 cm21 Broad peak 3,650–3,800 cm21 m OH, adsorbed H��O��H,

Broad peak at 3,100 cm21 ¼¼C��H stretching

2,902 cm21 m as CH2, m C��Hx organic groups

2,100 cm21 SCN

1,780 cm21 organics, C��O

1,600 cm21 1,620 cm21 H��O��H, molecular

1,410, 1,390 cm21 C��H in plane bending, m CH2��O

941 cm21 m as Si��OH

860 cm21 SCN peak

802 cm21 ms Si��O��Si, m as Si��C,

Si��O��Si��CnHmBroad peak at 780 cm21 Broad peak at 780 cm21 with

reduced intensity

m SiO��C2H5


interaction between the interlayer cations and electron

lone pairs belonging to adjacent oxygen atoms of oxy-

ethylene ligands [22]. The increase of comparative inten-

sity of 2,060 cm21 shows the disintegration of PEO/

PEO:SiO2 crystalline phase. The peak at 860 cm21 (after

salt doping) assigned as ��CH2 rocking vibrations of the

methylene group in gauge conformation as in polymer

salt complex [23]. The decrease in intensities of various

characteristic peaks (triplet band of PEO, 1,280, 1,360,

and 3,100 cm21) confirm the decrease in crystallinity af-

ter the formation of CPE.

Differential Scanning Calorimetry

The DSC curve of pure PEO, PEO:SiO2 with different

filler concentrations and x(PEO:SiO2):(1 2 x)NH4SCN

are shown in Fig. 5a and b, respectively. Diffractogram of

pure PEO film shows two peaks, one endothermic around

698C and another exothermic around 1058C. The first

peak is related to the melting of pure PEO while the sec-

ond is related to evaporation of adsorbed water. Above

1258C the sample starts dissociating. Addition of ceramic

filler (SiO2) in PEO matrix continuously reduces the melt-

ing temperature of the resulting system. The melting tem-

perature of polymer changes from 69 to 648C after the

addition of 30 wt% SiO2 and crystallinity of the host

polymer reduces as indicated by enthalpy change. This

effect is possibly due to the formation of more amorphous

domains with partial miscibility of filler with polymer

host. Similar observations have been recorded even after

the addition of salt. Further reduction in Tm was noticed

in case of CPEs. Such a reduction is possibly due to the

formation of amorphous PEO:NH4SCN complexes as wit-

nessed in IR and XRD studies. The DHm and the calcu-

lated crystallinity of PEO:SiO2 and with NH4SCN are

lower than that of PEO film casted in water and is in

agreement of XRD results.

CONCLUSION

The experimental results show that ceramic filler SiO2

was able to reduce the crystallinity of polymer and

enhance the salt dissociation property in x(PEO:SiO2):

(1 2 x)NH4SCN. The intercalations of silica in PEO pro-

vide a huge interfacial area with better mechanical pro-

perty of the solid composite electrolyte. The complex for-

mation between the salt and the polymer was confirmed

by appearance of new bands in IR spectra and broadening

of the C��O��C vibrations. This also suggests that silica

is compatible with PEO and changes the morphology of

system through reduction in crystallinity of the complex.

The enhancement of amorphousness is favorable for the

ionic mobility in the PEO based solid polymer electrolyte.

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FIG. 5. DSC curve for the (a) xPEO þ (1 2 x) SiO2 and (b) 95 [xPEO

þ (1 2 x) SiO2] þ 5 NH4SCN.


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Structure, interaction and thermal study in electrolyte of polyethylene oxide/silica/ammonium...

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