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: [email protected]
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.
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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.