Indian Journal of Chemistry

Vol. 53A, December 2014, pp. 1505-1512

Electrical conductivity of polyazomethine nanocomposites

Sandeep M Tripathia, †

, Devendra Tiwarib & Arabinda Ray

c, *

aDepartment of Chemistry, Sardar Patel University, V V Nagar 388 120, Gujarat, India bDr K C Patel Research and Development Centre, Charotar University of Science & Technology, Changa 388 421, Gujarat, India

cP D Patel Institute of Applied Sciences, Charotar University of Science & Technology, Changa 388 421, Gujarat, India

Email: arabinda24@yahoo.co.in

Received 2 May 2014; revised and accepted 18 November 2014

Nanocomposites of polyazomethines have been prepared via in situ and ex situ addition of Ag and PbS nanoparticles.

Structural characterization of nanocomposites by X-ray diffraction shows formation of pure nanocrystalline Ag and PbS

with cubic structure. Transmission electron microscopy gives evidence for spherical nanoparticles distributed homogenously

within the polymer matrix. Electrical measurements show a significant increase in conductivity in some of the nanocomposites

with respect to the virgin polymers. Infrared spectroscopy reveals strong interaction between the nanoparticles and polymers

in these nanocomposites. Finally, a theoretical model based on PM6 molecular orbital calculations to explain the observed

changes in the electrical conductivities is suggested. It is concluded that increase in electrical conductivity is governed by

strong interaction between the polymer and the inorganic nanoparticles, resulting in considerable decrease of energy

difference between the highest occupied molecular orbital and lowest unoccupied molecular orbital.

Keywords: Polymer nanocomposites, Composites, Nanocomposites, Molecular orbital calculations, Vibrational

spectroscopy, Electrical conductivity

The study of organic conducting polymers having

good electrical conductivity has drawn the attention of

many researchers1-6

worldwide. The pioneering work

of Heeger7, Macdiarmid

8 and Shirakawa

9 gave new

direction in the field of organic conducting polymers.

Various types of quantum mechanical calculations

with different levels of sophistication10-15

have been

carried out to explicate the electrical conduction in

polymers. However, no single mechanism was valid

for all the polymers. We believe that the present

investigation provides a simple mechanism to

understand the conductivity in polyazomethines.

Another very important component of this

investigation is to explain the role of polymer-dopant

interaction in enhancing the conductivity of the

polymer nanocomposites.

We have in our earlier studies16-18

reported simple

Pariser-Parr-Pople (PPP) calculations on certain

organic polymers, the limitations of which are well

known. Recently, we carried out all valence molecular

orbital calculations on a series of polyazomethines

using PM3, to arrive at a mechanism of conduction19

.

In continuation of the said work, it was thought

useful to have a further look into the nature of

polymer nanoparticle interaction in the composites.

Consequently, we carried out all valence molecular

orbital calculations using PM620

on a new series of

polyazomethines. A typical unit employed for

calculations is shown in structure (I).

Our interest in aromatic polazomethines, also

known as poly-Schiff bases is due to the fact that

these conjugated polymers have promising

applications in electronics, optoelectronics and

photonics21-23

and are attractive particularly for the

structure–property relationship. Krebs and

Jorgensen24

studied the effect of fluorination in

—————— †Present address: Pidilite Industries, Thane 400 601, Mumbai,

India.

Representative unit of polymer (Ib) employed for calculation.

(I)

INDIAN J CHEM, SEC A, DECEMBER 2014

1506

semiconducting polyazomethines to investigate the

carrier mobility and carrier lifetime. The azo

compounds have been demonstrated to be useful in

solar cell applications25,26

and the poly-Schiff bases

containing aromatic moieties are expected to provide

π conjugated backbone for electrical conduction.

Polymer nanocomposites with inorganic materials

have drawn the attention of many researchers. These

composites have demonstrated many interesting

properties27,28

. We prepared a few polymer

composites with nano Ag and PbS to examine

whether any change in electrical conductivity is seen

and if so why? The nanoparticles used herein have

been prepared in two ways: (i) using micro-emulsion

method and the particles so obtained were used for

preparing composites, and, (ii) In situ method, where

the nanoparticles were synthesized within the polymer

matrix. TEM has been employed, whenever

necessary, to obtain the size of the nanoparticles. The

IR spectra of these composites were obtained and

analyzed for the polymer nanoparticle interaction.

PM6 calculations have been carried out for the

polymer nanocomposites to understand the effect of

the inorganic nanoparticles on the electronic property

of the polymers. Two very important observations

are: (i) strong interaction (derived from IR data) of

polymer with nanoparticles leads to substantial

increase in electrical conductivity, and, (ii) when in

polymer composite the difference in energy between

HOMO and LUMO decreases significantly compared

to virgin polymers and the conductivity increases

substantially.

Materials and Methods

Analytical grade reagents were employed in this study. The solvents were purified wherever required. IR spectra of dyes, polymers and nano composites were obtained on Thermo FTIR spectrometer (Nicolet 6700) in KBr pellets. Solartron 1260 impedance/Gain Phase analyzer was employed to obtain the AC

conductivity of samples by varying the frequency in the range 100 Hz to 5 MHz at room temperature (35 °C). The samples were prepared from the powder polymers and nanocomposites, compressed (pressure 3000 lbs/in

2) to pellets using hydraulic press. The unit

of the AC conductivity is mho.cm-1

throughout the

work presented here.

Synthesis of azo bis-aldehydes and polyazomethines

Literature method29

was followed for the

preparation of the azo bis aldehydes, which involved

two steps, viz, tetraazotization of diamine followed by

the coupling of the azo compound with hydroxyl

aldehyde to form bisaldehydes. Three azo

bisaldehydes (azo dyes) were synthesized from the

three diamines: 4, 4´-diamino diphenyl benzamide

(abbreviated as DDB), o-tolidine (abbreviated as

OTOL) and p-diamino azobenzene (abbreviated as

AAB). The nomenclature of these azo dyes is as

follows:

(i) Coupling of DDB with o-vanillin (Dye I)

(ii) Coupling of OTOL with o-vanillin (Dye II)

(iii) Coupling of AAB with o-vanillin (Dye III)

The results of CHN analysis (obtained from Perkin

Elmer PE 2400) of these azo compounds are given in

Table S1 (Supplementary Data). These azo compounds

were employed to obtain polyazomethines30-32

. In

addition to the three diamines, DDB, OTOL and AAB,

the following four more diamines: (i) 4, 4´–diamino

diphenyl sulfonamide (abbreviated as DDSA),

(ii) 4, 4´–diamino diphenyl sulfone(abbreviated as

DDS), (iii) p-phenylene diamine (abbreviated as PPD)

and (iv) 4,4´–diamino diphenyl ether (abbreviated as

DDE), were also employed to prepare the polymers.

Each diamine (0.01 M) in 50 mL DMF was added

slowly to appropriate azo bis aldehyde (0.01 M)

dissolved in 150 mL of DMF containing a few drops

of acetic acid taken in a 250 mL three necked round

bottom flask. The contents of the flask were heated

for 30 h at 50-60 °C and the reaction mixture was

cooled to room temperature and poured into 100 mL

distilled water. The solid polymers obtained were

washed with hot acetone/methanol several times until

the filtrate was colorless. The polymers were

characterized by IR spectroscopy.

The role of polymer nanoparticles interaction

on the electrical conductivity of the polymer

nanocomposites was studied. Nanocomposites were

prepared from polymers: (i) with nanoparticles of Ag

and PbS obtained from micro-emulsion and (ii) via

in situ preparation of nanoparticles of Ag and PbS.

Two different ways of making composites were

employed to conclusively prove that it is only the

polymer nanoparticle interaction that will change the

conductivity.

Synthesis of nanoparticles of Ag and PbS from

microemulsions

The nanoparticles of Ag and PbS were obtained

from microemulsions. The microemulsion system (I)

consisted of surfactant Triton X-100, co-surfactant

TRIPATHI et al.: ELECTRICAL CONDUCTIVITY OF POLYAZOMETHINE NANOCOMPOSITES

1507

n-butanol and solvent cyclohexane. Solutions (0.1M)

of each of the salts, AgNO3 and Pb(NO3)2, were

prepared in de-ionised water. By careful addition

of aqueous salt solution to TritonX-100/solvent/

n-butanol system in 250 mL iodine flasks, it

was possible to identify visually the clear region of

the microemulsion. The other microemulsion

(II) consisted of either Na2S (for PbS) or formalin

(for Ag). The microemulsion I and II were mixed

under constant stirring for about 5 min to ensure

completion of reaction. Ultrasonication was carried

out for 5 min to ensure completion of reaction. The

particles thus obtained were washed with acetone

untill free from surfactant. A high speed centrifuge

(10000 rpm for 10 min) was used to settle the

particles from suspension and characterized by TEM

(Philips Technai 20) (Fig. 1) and XRD (Philips Xpert

MPD) data.

The observed XRD lines (2θ) for Ag nanoparticles

are: 38.15o

(111), 44.32o (200), 64.45

o (220), 77.55

o

(311). 2Theta values match well with cubic Ag phase

(JCPDS file No. 04-0783). The XRD of PbS nano

particles showed mainly peaks at (2θ) values of

25.8(111), 29.9 (200), 43.2 (220), 50.7 (311) and 53.5

(222) (PbS: JCPDS file no.05-0592). The Miller

indices correspond to face centred phase.

Preparation of polymer nanocomposites

Solution blending of inorganic nanoparticles into polymer

Only a few polymers were taken to prepare the

composites. The polymer (250 mg) was dispersed

(swollen) in 100 mL DMF by stirring in 250 mL

stoppard conical flask kept in a shaker. The solution

was taken out of the shaker occasionally and

sonicated to obtain a dispersed polymer solution. The

polymers were partially soluble in DMF and remained

finely dispersed after 48 h. The respective

nanoparticles dispersed in acetone were sonicated and

immediately added to the polymer in DMF under

sonication. The polymers were allowed to precipitate

out. While precipitating, the nanoparticles got

encapsulated into the polymer matrix. The composites

thus obtained were filtered and washed thoroughly

with acetone and dried.

Infrared spectra and AC conductivity of the

polymer composites were obtained as discussed

earlier. The TEM (Philips Technai 20) micrographs of

some of the composites are shown in Fig. 2. It may be

noted that particles embedded in polymer matrix are

of nano dimensions.

In situ preparation of nanoparticles to obtain polymer

nanocomposites

In this method the nanoparticles were synthesized

in situ resulting in polymer nanocomposites. The

method similar to the one described in the preceding

section to obtain dispersed polymer solution was used

in this case also.

To obtain polymer the silver nanocomposites,

silver nitrate was added to the dispersed polymer

solution and sonicated for 5 min to make it soluble.

Formalin was added to this mixture to reduce silver

nitrate to silver. The whole mixture was then

sonicated at room temperature for another 10 min and

kept in dark for 24 h. The polymer composite with Ag

nanoparticles was precipitated out by adding 10 mL

doubly distilled water to the mixture. The polymer

was filtered, washed several times with alcohol and

then with acetone using an ultrasonicator and finally

dried in vacuum desiccators.

TEM micrographs of some of these composites are

shown in Fig. 3. The micrographs clearly show that

Fig. 1—TEM images of nanoparticles (a) Ag and (b) PbS.

INDIAN J CHEM, SEC A, DECEMBER 2014

1508

the particles embedded in polymer matrix are of nano

dimensions. The XRD of the composites also shows

the presence of nanosized Ag in the polymers. A

typical XRD is shown in Fig. 4.

To obtain the polymer PbS nanocomposites,

Pb(NO3)2 was dissolved in polymer solutions in

DMF followed by addition of stoichiometric amount

of sodium sulphide (50 mL aqueous solution).

The rest of the procedure was similar to that followed

for silver doping. The PbS nanoparticles so

synthesized got entrapped in the precipitated

polymer matrix. TEM micrographs are shown in

Fig. 3 and XRD in Fig. 4.

The average crystallite size, as calculated

employing Scherrer relation, from broadening of

(111) XRD peak for Ag and PbS nanoparticles was

8 and 30 nm, respectively.

Results and Discussions The IR peaks are assigned following Dyer

33 and

Silverstein34

and these references are not quoted

further in the text.

IR spectra of the dyes and polymers

IR spectral data were employed to confirm the

formation of azo bisaldehyde dyes. The formation of

respective dyes was confirmed by the presence of

Fig. 2—TEM images of polymer composite with nanoparticles of (a) Ag and (b) PbS prepared by microemulsion.

Fig. 3—TEM bright field images with electron diffraction of polymer nanocomposite prepared in-situ. [(a, c) Ag; (b,d) PbS].

TRIPATHI et al.: ELECTRICAL CONDUCTIVITY OF POLYAZOMETHINE NANOCOMPOSITES

1509

C=O stretching at ~1650 cm-1

or 1680 cm-1

,

depending on whether salicylaldehyde or vanillin was

the coupling agent in the preparation of the dye. The

dyes have absorptions at ~1575-1620 cm-1

that can be

assigned to coupled vibrations of N=N and C=C

stretching and NH bending (in case of DDB).

The disappearance of the C=O stretching in the

condensation product of bisaldehydes and diamines is

indicative of the formation of polyazomethines. The

C=O stretching of the benzamide moiety contributes

primarily to the peak at 1618 cm-1

. The C=N

stretching is likely to be distributed in absorptions at

1618 and 1595 cm-1

. The N=N stretching also

contributes to the peak 1595 cm-1

.

The polymers of 4, 4´-diamino diphenyl ether have

a strong absorption at ~1230 cm-1

due to C-O

stretching of the ether linkage. In all the polymers, the

absorptions due to S=O stretching is mainly

distributed in the region of 1000-1200 cm-1

. The CH

out-of-plane bending in the para disubstituted

aromatic ring was seen at ~840 cm-1

in all the

compounds. The O=S=O bending modes were

observed at 625 cm-1

and 610 cm-1

. In all the

compounds, C-S stretching was traced to the

frequency at ~705 cm-1

, while the absorption at

~1300-1320 cm-1

was assigned to C-N stretching.

All Valence MO calculation with PM6 method

Unit representative of each polymer consisting of

one dye (bis-aldehyde) moiety in which each

aldehyde is replaced by diamine has been employed

for the calculation. A typical representative unit of a

polymer Ib (DDB-VAN + 4, 4´-diamino diphenyl

sulfonamide) used for calculation is shown in (I).

Similar units of other polymers have been subjected

to PM6 calculation. The abbreviation of the polymers

are shown in Table 1. Since we are concerned

with the difference in energies of MOs in virgin

and polymer composites, we did not use the

ab initio/DFT methods for calculating the same.

We believe higher level semi-empirical method

such as PM6 will provide a relative idea of the

changes in MO-energy due to polymer nanoparticle

interaction, when all the concerned molecules

are subjected to the same method of calculation.

Herein we chose PM6, because other popular

methods like AM1 and PM3 do not have the

parameters for Ag.

The basic assumptions to explain the conductivity

in light of the results of the molecular orbital

calculations are already discussed in our earlier

paper19

. However, it is known that the energy

difference (∆E) between HOMO and LUMO plays an

important in conduction. Hence, only the value of ∆E

of the virgin polymer is considered and compared

with the composite to explain the change, if any, in

conduction of the composites.

Polymer nanoparticle interaction

The IR spectra of a few polymer nanocomposites

were recorded. The composites obtained in this study

are designated as polymer (nanoparticles –I/M),

where I and M stand for in situ and microemulsion

methods respectively.

We first examine the polymer nanocomposites of

polymers derived from dye I. IR spectra are so chosen

as to demonstrate different types of polymer

nanoparticle interaction. The IR spectra of polymers

Ic and Id showed significant changes when

composites are prepared with nano Ag, indicating

strong polymer nanoparticle interaction. Hence,

substantial increase in conductivity is seen in these

Fig. 4—X-ray diffractogram of (a)PbS and (b) Ag doped polymer nanocomposite prepared by in situ method.

INDIAN J CHEM, SEC A, DECEMBER 2014

1510

(Table 2) composites. However, the IR spectra of

I(f/g/h) do not change noticeably in their

respective composites, suggesting weak polymer

nanoparticles interaction and as expected, no

significant change is seen in conductivity.

The interaction of nanoparticle with C=N, N=N

and to an extent with sulfone moiety of the polymer,

results in substantial shifts in IR peaks of

some polymers. The IR spectra (Fig. 5) of polymers

Ic and If demonstrate respectively, strong and

weak interaction of nanoparticle with polymer.

PM6 calculations for composites

To investigate the changes that take place in the

electronic property of the polymers in the polymer

nanocomposites, we carried out all-valence MO

calculation on the nanocomposites of polymers

(dye I) using PM6 method. We examined the

difference of energy (∆E) for different degree of

polymer nanoparticle interaction. For this, each

nanoparticle was allowed to interact first at a

particular site either N or O in the respective

polymer unit (I). The composite was then subjected to

PM6 calculations to obtain the MO energies. A

similar process was repeated allowing the

nanoparticle to attack separately all other sites and

finally all the possible sites at same time. It is

seen that as the nanoparticles attack more sites,

the ∆E decreases proportionally. However only in a

few cases, when all the possible sites are attacked by

the nanoparticle at a time, the ∆E values are

sufficiently low and in these composites, there is

substantial increase in conductivity (Table 2).

It may be noted that in such polymer

nanocomposites, the IR spectra show strong

polymer nanoparticle interaction. Interestingly,

the Ag nanocomposites of polymers which show

good electrical conductivity have not only low

value of ∆E but also comparatively unstable HOMO;

the ones with low increase in conductivity have

not only high ∆E, but also quite stable HOMO.

The unstable HOMO possibly allows the

Table 1—PM6 calculations on the repeating unit in polymers derived from the dyes I, II and III

Polymer

(Conductivity,

mho cm-1)

Energy of frontier

orbitals (eV)

Polymer

(Conductivity,

mho cm-1)

Energy of frontier

orbitals (eV)

Polymer

(Conductivity,

mho cm-1)

Energy of frontier

orbitals (eV)

Dye I + DDSA

(1.73 ×0-6) Ib

HOMO = - 8.042

LUMO = - 1.633

∆E = 6.409

Dye II + DDSA

(1.53 × 10-6) IIb

HOMO = - 7.988

LUMO = - 1.455

∆E = 6.533

Dye III + DDSA

(1.94 × 10-6) III b

HOMO = -8.076

LUMO = - 1.681

∆E = 6.395

Dye I + DDS

(1.49 × 10-6) Ic

HOMO = - 8.789

LUMO = - 1.706

∆E = 7.083

Dye II + DDS

(1.08 × 10-6) IIc

HOMO = - 8.737

LUMO = - 1.426

∆E = 7.311

Dye III + DDS

(2.65 × 10-6) IIIc

HOMO = -8.794

LUMO = - 1.744

∆E = 7.050

Dye I + DDB

(1.41 × 10-6) Id

HOMO = - 8.314

LUMO = - 1.782

∆E =6.532

Dye II + DDB

(1.25 × 10-6) IId

HOMO = - 8.118

LUMO = - 1.300

∆E = 6.818

Dye III + DDB

(1.35 × 10-6) III d

HOMO = - 8.244

LUMO = - 1.734

∆E = 6.51

Dye I + PPD

(1.92 × 10-6) Ie

HOMO = - 8.131

LUMO = -1.661

∆E = 6.47

Dye II + PPD

(1.41 × 10-6) IIe

HOMO = - 8.094

LUMO = - 1.379

∆E = 6.715

Dye III + PPD

(1.46 × 10-6) III e

HOMO = - 8.239

LUMO = - 1.635

∆E = 6.604

Dye I + DDE

(1.24 × 10-6) If

HOMO = - 8.336

LUMO = - 1.695

∆E = 6.641

Dye II + DDE

(9.98 × 10-7) IIf

HOMO = - 8.326

LUMO = - 1.427

∆E = 6.899

Dye III + DDE

(1.18 × 10-6) IIIf

HOMO = - 8.405

LUMO = - 1.679

∆E = 6.731

Dye I + OTOL

(1.07 × 10-6) Ig

HOMO = - 8.167

LUMO = - 1.685

∆E = 6.482

Dye II + OTOL

(8.60 × 10-7) IIg

HOMO = - 8.048

LUMO = - 1.394

∆E = 6.654

Dye III + OTOL

(1.09 × 10-6) III g

HOMO = - 8.211

LUMO = - 1.652

∆E = 6.559

Dye I + AAB

(1.46 × 10-6) Ih

HOMO = - 8.258

LUMO = - 1.292

∆E = 6.966

Dye II + AAB

(1.20 × 10-6) Iih

HOMO = - 8.354

LUMO = - 1.340

∆E = 7.014

Dye III + AAB

(1.83 × 10-6) III h

HOMO = - 8.363

LUMO = - 1.709

∆E = 6.659

Table 2—Conductivity of polymer Ag composites

(derived from dye I)

Polymera Conductivity (mho cm-1) ∆E

(eV)

EHOMO

(eV) Polymer

(Undoped)

Polymer

(Doped)

Ic 1.49 × 10-6 (Ag-M) 2.07 × 10-3 2.47 -6.463

Id 1.41 × 10-6 (Ag-M) 1.10 × 10-4 2.52 -6.128

Ie 1.92 × 10-6 (Ag-M) 8.62 × 10-4 2.50 -6.267

If 1.24 × 10-6 (Ag-M) 8.55 × 10-5 3.80 -6.936

Ig 1.07 × 10-6 (Ag-M) 2.50 × 10-5 4.30 -7.547

Ih 1.46 × 10-6 (Ag-M) 2.37 × 10-5 4.8 -7.977 aDesignation of the polymers as in Table 1.

TRIPATHI et al.: ELECTRICAL CONDUCTIVITY OF POLYAZOMETHINE NANOCOMPOSITES

1511

comparatively easy HOMO to LUMO

electron transfer. This together with low ∆E value

provides better electrical conductivity in these

Ag composites.

The nano Ag and PbS composite of polymers

derived from dye II showed similar IR behavior

(Fig. 6) as discussed in the preceding section, i.e.,

wherever there is strong polymer nanoparticle

interaction, a substantial increase in conductivity is

seen. PM6 calculations were carried out for these

polymer composites in a similar manner as for

nanocomposites of polymers derived from dye I. First

the nanoparticles were allowed to attack separately all

the possible sites of the respective polymer unit as

depicted in (I) and then all possible sites at same time.

As above, PM6 calculations show that composites

with low ∆E have good conductivity (Table 3). In

these polymers also, a few composites with Ag, have

low ∆E and registered a substantial increase in

electrical conductivity. Relatively high ∆E values and

quite stable HOMO do not favor electron

transfer from HOMO to LUMO in PbS composite

polymers (Table 3). Hence, in the polymer

composites with PbS, a very low increase in

conductivity is seen. It is interesting to note that

all the polymer composites with Ag have relatively

unstable HOMO.

Only Ag nanoparticles composite with

polymers derived from dye III were obtained. The results of PM6 calculations for the polymer composites along with conductivity data are shown in Table 4. It may be noted that the IR spectra and results of PM6 calculation for these polymer nanocomposites follow the same trend as seen

for other polymers. Only the nano Ag composites

of polymers IIId and IIIh having low ∆E value and relatively unstable HOMO showed substantial increase in conductivity.

Fig. 6—IR spectra of polymers IIc. [U stands for virgin polymer,

Ag-M stands for polymer doped with Ag nanoparticles obtained

from microemulsion method. PbS-I is for polymer composite

consisting of PbS nanoparticles prepared in situ of polymer

matrix].

Table 3—Conductivity of polymer Ag/ Pbs composites

(derived from dye II)

Polymera Conductivity (mho cm-1) ∆E (eV) EHOMO

(eV) Polymer

(Undoped)

Polymer

(Doped)

IIc 1.08×10-6 (Ag-M) 2.68×10-3 2.80 -5.981

(Ag-I) 1.20×10-3

(PbS-I) 3.59×10-6 4.70 -7.120

IId 1.25×10-6 (Ag-M) 6.28×10-4 3.4 -6.645

(Ag-I) 8.00×10-4

(PbS-I) 6.41×10-6 5.30 -7.51

IIe 1.41×10-6 (Ag-M) 1.38×10-5 3.52 -6.668

(Ag-I) 2.92×10-5

(PbS-I) 6.94×10-6 5.49 -7.51

IIf 9.98×10-7 (Ag-M) 7.92×10-5 4.3 -8.118

(Ag-I) 9.02×10-5

(PbS-I) 3.31×10-6 5.06 -7.402

IIg 8.60×10-7 (Ag-M) 4.54×10-3 1.6 -7.276

(Ag-I) 4.12×10-3

(PbS-I) 3.91×10-6 5.04 -7.138

IIh 1.20×10-6 (Ag-M) 3.14×10-4 3.7 -6.869

(Ag-I) 1.67×10-4

(PbS-I) 4.46×10-6 5.18 -7.559 aDesignation of the polymers as in Table 1.

Fig. 5—IR spectra of polymers Ic and If. [U stands for

virgin polymer and Ag-M stands for polymer doped with

Ag nanoparticles obtained from microemulsion method].

INDIAN J CHEM, SEC A, DECEMBER 2014

1512

Conclusions

The polymer composites with low values of ∆E and

unstable HOMO show reasonably good electrical

conductivity. This is found only in some polymer

composites with Ag nanoparticles. In such

nanocomposites, strong nanoparticle polymer

interaction is seen from the IR spectral data. It is

important to note that in many polymer Ag composites,

MO calculation shows no substantial decrease in ∆E.

IR spectra also suggest weak interaction. In such cases

as expected, the composites do not register any

substantial increase in conductivity. Also, some

polymer composites with Ag nanoparticle have

reasonably low ∆E, but their HOMO is quite stable;

they do not show any significant increase in

conductivity. It is to be noted that in all PbS doped

polymers, the polymer nanoparticles interaction is

weak; ∆E values are relatively high and all have highly

stable HOMO. As expected, these PbS nanocomposites

do not show any substantial increase in conductivity.

This study opens up an interesting area in polymer

nanocomposites. By suitably preparing polymer

nanocomposites, where the interaction is strong

between the polymers and nanoparticles, the electrical

conductivity can be increased substantially. These

polymer nanocomposites can then be utilized for

various optoelectronic devices such as photodetectors,

photovoltaic cells, etc.

Supplementary Data Supplementary data, i.e., Table S1, is available in the

electronic form at http://www.niscair.res.in/jinfo/ijca/

IJCA_53A(12)1505-1512_SupplData.pdf.

Acknowledgement

The authors gratefully acknowledge the assistance

received from Prof. D K Kanchan and Mr. Manish

Jayswal of Department of Physics, Faculty of Science,

The Maharaja Sayajirao University, Vadodara,

Gujarat, India for the conductivity of the samples. The

authors also recognize the services of Sophisticated

Instrumentation Centre for Advanced Research and

Testing (SICART), Vallabh Vidyanagar, Gujarat,

India for the transmission electron micrographs.

References 1 Garito A F & Heeger A J, Acc Chem Res, 7 (1974) 232.

2 Patil A O, Heeger A J & Wudl F, Chem Rev, 88 (1988)183.

3 Baughman R H, Bredas J L, Chance R R, Elsenbaumer R L

& Shaklette L W, Chem Rev, 82 (1982) 209.

4 Bredas J L, Cornil K, Meyers F & Beljonne D, Handbook of

Conducting Polymers, (Marcel Dekkar, New York) 1998.

5 Li H, Lambert C & Stahl R, Macromolecules, 39 (2006) 2049.

6 Ye G, Janzen N & Goward G R, Macromolecules, 39 (2006)

3283.

7 Heeger A J, Rev Mod Phys, 73 (2001) 681.

8 MacDiarmid A G, Rev Mod Phys, 73 (2001) 701.

9 Shirakawa H, Rev Mod Phys, 73 (2001) 713.

10 Berlinsky, J F Carolan J F & Weiler L, Solid State Comm,

19 (1976) 1165.

11 Salzner U, Pickup P G, Poirier R A & Lagowski J B, J Phy

Chem, A 102 (1998) 2572.

12 Su W P, Schrieffer J R & Heeger A J, Phys Rev Lett,

42 (1979) 1698.

13 Heeger A J, Kivelson S, Schrieffer J R & Su W P, Rev Mod

Phys, 60 (1988) 781.

14 Koslowski T, Jurjiu A & Blumen A J, Phys Chem B, 108

(2004) 3283.

15 Matus M H, Garza J & Galvan M J, Phys Chem, 110 (2006)

1172.

16 Ray A & Suthar B P, Polymer, 25 (1984) 10.

17 Ray A & Makhija K K, Indian J Chem, 29A (1990) 321.

18 Bhatt V D & Ray A, Synth Met, 92 (1998) 115.

19 Tripathi S, Vasudev I & Ray A, J Macromol Sci B, 50 (2011)

1195.

20 Stewart J J P, J Mol Model, 13 (2007) 1173.

21 Jenekhe S A & Yang C J, Ind Eng Chem Res, 38 (1999) 1759.

22 Yang C J, Jenekhe S A, Meth J S & Vanherzeele J Chem

Mater, 3 (1991) 985.

23 Fisher W, Stelzer F, Meghdadi F & Leising B, Synth Met,

76 (1996) 201.

24 Krebs F C & Jorgensen S M, Synth Met, 142 (2004) 181.

25 Muto T, Ikegami M, Kobayashi K & Miyasaka T, Chem

Lett, 36 (2007) 804.

26 Ryoichi K, Han L, Ryohsuke Y, Ashraful I & Takehito M,

J Photochem Photobiol Chem, 164 (2004) 123.

27 Winey K I & Vaia R A, MRS Bull, 32 (2007) 314.

28 Gangopadhyay R & De A, Chem Mater, 12 (2000) 608.

29 Hodgkin J H & Heller J, Macromolecules, 2 (1969) 556.

30 Park S B, Kim H, Zin W C & Jung J C, Macromolecules,

26 (1993) 1627.

31 Patil A O, Ikenoue Y, Basescu N, Colaneri N, Chem J, Wudl

F & Heeger A J, Synth Met, 20 (1987) 151.

32 Chiang C K, Druy M A, Gau S C, Heeger A J, Louis E J,

MacDiarmid A G, Park Y W & Shirakawa H, J Am Chem

Soc, 100 (1978) 1013.

33 Dyer J R, Applications of Absorption Spectroscopy of Organic

Compounds, (Prentice-Hall of India, New Delhi) 1997.

34 Silverstien R M &Webster F X, Spectrometric Identification

of Organic Compounds, (Wiley, London) 1997.

Table 4—Conductivity of polymer Ag composites

(derived from dye III)

Polymera Conductivity (mho cm-1) ∆E

(eV)

EHOMO

(eV) Polymer

(Undoped)

Polymer

(Doped)

IIIc 2.65 × 10-6 (Ag-M) 9.92 × 10-5 3.3 -6.940

IIId 1.35 × 10-6 (Ag-M) 2.39×10-4 3.4 -6.421

IIIe 1.46 × 10-6 (Ag-M) 3.49 × 10-6 4.4 -7.296

IIIf 1.18 × 10-6 (Ag-M) 6.35 × 10-5 3.7 -6.867

IIIg 1.09 × 10-6 (Ag-M) 6.97 × 10-6 4.3 -7.379

IIIh 1.83 × 10-6 (Ag-M) 4.23 × 10-4 3.3 -6.405 aDesignation of the polymers as in Table 1.