Structural, optical, thermal and morphological studies were performed on pure Polyvinyl alcohol/ Methacrylic Acid e Ethyl Acrylate (PVA/MAA:EA (50:50)) blend and PVA/MAA:EA blend filled with different concentrations (5, 10 and 15 wt) of Lithium Perchlorate (PVA/MAA:EA: LiClO4) prepared by a solution casting method.
Trang 1Original Article
Thermal, structural, optical and electrical properties of PVA/MAA:EA
Perchlorate
T Siddaiaha, Pravakar Ojhaa, N.O Gopala, Ch Ramua,*, H Nagabhushanab
a Department of Physics, Vikrama Simhapuri University PG Centre, Kavali, 524201, India
b CNR Rao Centre for Advanced Materials Research, Tumkur University, Tumkur, 572103, India
a r t i c l e i n f o
Article history:
Received 18 July 2018
Received in revised form
17 November 2018
Accepted 18 November 2018
Available online 27 November 2018
Keywords:
Polymer
Lithium Perchlorate
PVA/MAA:EA blend
FTIR
TGA
X e ray
SEM and optical energy
a b s t r a c t
Structural, optical, thermal and morphological studies were performed on pure Polyvinyl alcohol/ Methacrylic Acid e Ethyl Acrylate (PVA/MAA:EA (50:50)) blend and PVA/MAA:EA blend filled with different concentrations (5, 10 and 15 wt%) of Lithium Perchlorate (PVA/MAA:EA: LiClO4) prepared by a solution casting method XRD patterns demonstrated that the peak intensity at 2q¼ 19.5decreased and the bandwidth increased with increasing the concentration of LiClO4, which implied a decrease in the degree of crystallinity and hence caused an increase in the amorphous nature UVe Visible analysis revealed that the values of both direct and indirect band gaps were decreased with increasing LiClO4
content in the polymer host This indicated the formation of charge transfer complexes between the polymer blend and thefiller The dTGA curves show three different steps of weight loss This is due to the loss of water adsorbed, the elimination of the side chains, and the decomposition of the main chain For LiClO4filled PVA/MAA:EA, FTIR spectra showed disappearance of some bands with the change in their intensities as compared to pure PVA/MAA:EAfilm This indicated considerable interaction between the polymer blend and LiClO4filler SEM images of the polymer blend films complexed with LiClO4suggested the presence of a structural rearrangement of the polymer chains The electrical conductivity of the preparedfilms was measured using the impedance analyzer in the frequency range from 1 Hz to 5 MHz
at room temperature It was observed that the conductivity increased with increase of the Liþion concentration
© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
1 Introduction
Nowadays, the rechargeable battery market is about 27.7 billion
dollars and in 2019 it has been assessed to be 54.9, a fast growth is
expected in the rechargeable battery market due to the increase in
the demands such as laptops, mobile phones, e-books, watches,
toys, automotive sectors and transportation[1] Liþion batteries are
dominant in the electronic devices market due to their compact
and lightweight, safety, reliability, cost, design, efficiency, being
more environmentally friendly, the highest energy density, high
average discharge rate (~37 V) and the absence of memory effects
among other types of batteries[2e4]
Materials based on the polymers originate from the need for self-standing, leak-free battery systems The three types of polymer materials are single polymer electrolyte (SPE), composite polymer electrolyte (CPE) and polymer blend electrolyte (PBE) In PBE, two different polymers having complementary properties i.e one polymer showing good affinity with the liquid electrolyte and the other showing proper mechanical properties are used The most used polymer blend electrolytes are (PVAe PANI), (PVA e PAN), (PVPe PVA), (PMVEMA e PVA), (PVA e PEI), (PVA e PVdF), (PEO e PVA), (PVA e PAA), (PVA e PEG), (PEO e PMMA), (PVC e PS), (Chitosane PVA), (PVA e NyC), (PEMA e PVdF), (PVA e NaAlg) and its copolymers P(VDFe TrFE), P(VDF e HEP) and P(VDF e CTFE) There has been considerable interest in polymer blends in recent decades, owing to their better combination of physical properties, biocompatibility and potential applications than those
of single components [5,6] It is generally recognized that the properties of the polymer blends are greatly dependent on their
* Corresponding author.
E-mail address: chramu8@gmail.com (Ch Ramu).
Peer review under responsibility of Vietnam National University, Hanoi.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
https://doi.org/10.1016/j.jsamd.2018.11.004
2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license
Journal of Science: Advanced Materials and Devices 3 (2018) 456e463
Trang 2miscibility and phase behavior When two polymers experience
miscibility, a well-ordered microstructure is obtained, which gives
the mixture certain unique physical properties according to the
formation of the microphase configuration The resulting
micro-phase configuration can induce drastic changes in all the
proper-ties (Optical, thermal, electrical…etc.) that are different from those
of the individual polymers Therefore, the miscibility and phase
behavior of polymer blends have been the subject of numerous
studies[7]
Polyvinyl alcohol (PVA) has received a great deal of attention
due to its high dielectric strength, good charge storage capacity and
dopant dependent electrical properties either pure or composite
with other materials [8] PVA is well known for its low cost,
excellent transparency, flexibility, toughness, nontoxicity, water
solubility, biodegradability and gas barrier properties Hence, it is
widely used in controlled drug delivery systems, membrane
prep-arations, recycling of polymers, packaging textiles and leather
in-dustries because of excellent film-forming characteristics The
optical uses of PVA are related to the delay, polarization and
filtering of light and to photography[9]
Methacrylic Acid e Ethyl Acrylate (MAA:EA) copolymer has
been placed at the center amongst the copolymers due to its
ad-vantages like easier processability, good environmental stability
and transparency It has substantial charge storage capacity and
dopant dependent electrical and optical properties Acrylates are a
group of easily UV- polymerizable monomers with an unending
possibility of polymer chain compositions which can thus be
optimized to meet the desired material properties Different types
and amounts of selected monomer units, the length and
compo-sition of the main polymer chain as well as chemistry of the side
chains can be varied and the polymer structure can be further
altered by cross-links[10,11]
In order to benefit from the advantages of the polymer and
copolymer, in this work, PVA and MAA:EA have been blended at a
fixed weight ratio of 50:50 and Lithium has been added to provide
the charge carriers Blended host matrices also help to increase
ionic conductivity[12] Both PVA and MAA:EA contains electron
pairs that can coordinate with a cation from inorganic salt like Liþto
form polymer-salt complexes and hence produce ionic conduction
Electron pairs are formed on oxygen atoms of C¼ O and C e O e C
groups of PVA and hydrogen atoms in MAA:EA copolymer[13]
2 Experimental
MAA: EA copolymer (1:1) dispersion of 30 percent is a
disper-sion in water of a copolymer of Methacrylic Acid and Ethyl Acrylate
having an average relative molecular weight of about 250,000
(supplied by Merck Millipore India Ltd.) and high purity PVA of
molecular weight 17,000 in form of grains was provided by Merck C
Darmstadt, Germany Films of (thickness ~ 150 mm) pure PVA/
MAA:EA and different compositions of LiClO4complexedfilms of
(PVA/MAA:EA) were prepared by the solution cast technique in
different weight percent ratios (50.0:50.0:0), (47.5:47.5:5),
(45:45:10), (42.5:42.5:15) using double distilled water as a solvent
Required amounts of PVA, MAA: EA and LiClO4were dissolved in
double distilled water and the solutions were stirred magnetically
for 10e12 h to obtain a homogeneous solution and then poured into
polypropylene dishes and evaporated slowly at room temperature
for 48 h to obtain free-standing pure and dopedfilms at the bottom
of the dishes The thermal properties of the prepared samples were
studied using SEIKO thermal analysis system (TGAe 20) in the
presence of nitrogenflow from 40 to 700C, at the heating rate of
10C/min The X-ray diffraction patterns were performed using a
Siemens D5000 diffractometer with CuKaradiation (l¼ 1.5406 Å)
The preparedfilms were scanned at 2qangles with a step size of
0.02 between 0 and 40 FTIR spectra of the prepared samples were recorded using a PerkineElmer FTIR spectrometer, over a wavenumber range 500e4000 cm1 SEM images of the polymer blend electrolytefilms were characterized by Hitachi (TM e 3000 and He 8100) electron microscope with scanning attachment The optical absorption curves of thefilms were recorded in the range of
200e800 nm at room temperature using JASCO UV e VIS e NIR spectrophotometer (model e V.700) The electrical properties of the polymer electrolytefilms were studied using a Hitester 3532-50 LCR in the frequency range of 1 Hze5 MHz
3 Results and discussion 3.1 X-ray diffraction analysis X-ray diffraction analysis provides useful structural information, such as crystal structure, crystal size, strain, preferred orientation and layer thickness of a tested material Researchers used the X-ray diffraction to analyze a wide range of materials such as powders, thinfilms, nanomaterials and solid objects.Fig 1shows the XRD scans of pure PVA/MAA:EA (50:50) blend and PVA/MAA:EA blend filled with various weight fractions (5, 10 and 15 wt%) of Lithium Perchlorate (LiClO4) filler The observed diffractograms exhibit three peaks centered at about 2q¼ 19.5, 1.4and 0.6, which in-dicates the semi-crystalline nature of the PVA/MAA:EA polymer blendfilm[14] Thefirst one has a clear crystalline peak at a scat-tering angle 2q¼ 19.5which corresponds to a (1 1 0) reflection
[15] The present X-ray pattern revealed no significant changes in the positions of three peaks after complexation withfiller, the in-tensity of the diffraction peaks is further decreased This could be due to the interaction between the blend and filler, leading to decrease in the intermolecular interaction between the blend chains as well as the degree of crystallinity[16] As the Liþcontent
is increased in the polymer, the diffraction peaks become less intense, suggesting a decrease in the degree of crystallinity and a simultaneous increase in the amorphicity of these polymer elec-trolyte systems The decrease in crystallinity with increasing LiClO4 content in the blended sample involves a decrease in the number of
Fig 1 XRD patterns of (a) pure (50:50) and different concentrations (b) 5 wt% (c)
10 wt% and (d) 15 wt% of LiClO doped PVA/MAA:EA polymer blend films.
T Siddaiah et al / Journal of Science: Advanced Materials and Devices 3 (2018) 456e463 457
Trang 3hydrogen bonds formed between PVA and MAA: EA The peak at
2q¼ 19.5has been found to increase in broadness and decrease in
intensity as Liþion content increases and enhances the
complex-ation between the polymer blend and LiClO4[17]
Hodge et al.[18]established a relationship between the peak
intensity and degree of crystallinity They observed that the
in-tensity of the diffraction pattern decreases as the amorphous
na-ture increases by the addition of a dopant In the present work, no
sharp peaks were observed for higher concentrations of LiClO4salt
in the polymer, which indicates the dominant presence of the
amorphous phase [19] This amorphous nature leads to greater
ionic diffusion and high ionic conductivity, which can be observed
in amorphous polymers having aflexible main chain[20]
3.2 Ultraviolet and visible analysis
The optical absorption study can be used to gain the detailed
information about the band structure of solid materials In optical
absorption phenomena, an electron is excited to a higher energy
state from a lower energy state by the absorption of a photon of
sufficient energy in the transmitting radiation The electronic
transitions can be estimated from the changes in the transmitted
radiation The optical absorption coefficient (a) can be evaluated
from the absorbance by the following relation[21]
Absorption coefficientðaÞ ¼ 2:303 A
where A is the absorbance and d is the thickness of thefilms
The absorption coefficient (a) can be useful to determine the
optical energy band gap (Eg), which is an important parameter of
both organic and inorganic materials The optical energy band gap
of the preparedfilms was estimated by using Tauc's relationship
[22],
ðahyÞ ¼ B hy Eg
n
(2) where B is a factor that depends on the electronic transition
probability, which can be treated as the constant within the optical
frequency range and the index n represents the type of electronic
transition, which related to the distribution of the density of the
states For direct electronic transitions, n takes the values of 1/2 or
3/2 and for indirect transitions n is equal to 2 or 3, depending on
whether they are allowed or forbidden, respectively
When the direct and indirect band gap exist, the absorption
coefficient has the following dependence on the energy of the
incident photon,
ahy¼ B1
ahy¼ B2 hy Egi
2
(4) where Egdand Egiare the direct and indirect band gaps,
respec-tively, B1and B2are constants
Figs 2 and 3represent the plots of (ahy)2and (ahy)1/2versus
photon energy (hy) for pure and different weight fractions (5, 10
and 15 wt%) of LiClO4doped PVA/MAA:EA polymer blend
electro-lytefilms The direct and indirect band gap values are determined
by extrapolating the linear part of the curves (ahy)2and (ahy)1/2
versus photon energy (hy) to zero absorption value The evaluated
band gap values (both direct and indirect) are reported inTable 1
FromTable 1, it is clear that both direct and indirect energy band
gap values decrease with increasing in the LiClO4content in the
polymer blend The doped LiClO salt increases the disorder of the
polymer structure, which results in decreases in the optical band gap value Among all the prepared samples, the 15 wt% LiClO4 doped polymer blend electrolyte shows the minimum direct en-ergy band gap and indirect enen-ergy band gap value Hence it has more semiconducting nature than remaining PVA complexed polymer blend electrolytefilms[23]
3.3 Fourier transform infrared analysis Infrared spectroscopy has been used to identify interactions in the polymer blends FTIR spectroscopy is very sensitive to the
Fig 2 The plot of (ahy) 2 vs (hy) of (a) pure (50:50) and different concentrations (b)
5 wt%, (c) 10 wt% and (d) 15 wt% of LiClO 4 doped PVA/MAA:EA polymer blend elec-trolyte films.
Fig 3 The plot of (ahy) 1/2 vs (hy) of (a) pure (50:50) and different concentrations (b)
5 wt%, (c) 10 wt% and (d) 15 wt% of LiClO 4 doped PVA/MAA:EA polymer blend elec-trolyte films.
T Siddaiah et al / Journal of Science: Advanced Materials and Devices 3 (2018) 456e463 458
Trang 4formation of hydrogen bonds[24].Fig 4(aed) shows FTIR
trans-mittance spectra of PVA/MAA:EA (50:50) blend without and with
different concentrations 5, 10 and 15 wt % of LiClO4recorded at
room temperature in the region 500e4000 cm1 FTIR
trans-mittance band positions and their corresponding assignments are
presented inTable 2for all prepared compositefilms
Fig 4(a) shows the FTIR spectrum of pure PVA/MAA:EA blend
The bands at about 3135e3531 and 1436 cm1 belong to the
stretching and bending vibration of the hydroxyl group,
respec-tively[25] The band characterized for the methylene group (CH2)
asymmetric stretching vibration occurs at about 2934 cm1 The
band at about 1099 cm1corresponds to Ce O stretching of acetyl
groups present on the PVA backbone[16,26] The vibrational band
at about 1722 cm1is assigned to C¼ O stretching of PVA and
MAA:EA copolymer
The FTIR spectra of 5, 10 and 15 wt% of Lithium Perchlorate doped
films indicate a clear decrease in the intensity of the bands From
Fig 4, the following changes in the spectral features have been
observed for the PVA/MAA:EA (50:50) blend without and with
different concentrations of 5, 10 and 15 wt% of LiClO4 A broad and
very strong band observed at 3085e3539, 3135e3522 and
3119e3565 cm1for 5, 10 and 15 wt% of LiClO4complexedfilms,
respectively, arises from Oe H stretching frequency and is an
indi-cation of the presence of hydroxyl groups [24] With increasing
dopant concentration the width increases and intensity of these
bands is found to decrease compared to the pure PVA/MAA:EA blend
The vibrational peaks observed at 1099 and 1436 cm1for pure
blend are found to be absent in Liþ ion doped blend films The
disappearance of bands observed in blendfilm with Liþion doping
suggests the co-ordination or complexation of chlorine with the
blendfilm[27]
It was found that a small absorption band around 922 cm1is characteristic of the syndiotactic structure of the prepared samples Syndioactivity of PVA/MAA: EA samples induces dense molecular packing in a crystal, as well as stronger intermolecular hydrogen bonds, which in turn, are responsible for the disappearance of molecular motion[28] This band appeared in the spectra of pure blendfilm, but it disappeared in the spectra of the Liþion doped blend and this may be attributed to the addition of Lithium
3.4 Thermogravimetric analysis Thermal stability and degradability of the prepared samples were evaluated by thermogravimetric analysis[29] Moreover, the kinetics of the accompanied decomposition relation has been reviewed The sample weight decreases slowly as the reaction be-gins, then decreases rapidly over a comparatively narrow temper-ature range andfinally levels off as the reactants are used up The shape of the curve depends primarily upon the kinetic parameters involved, i.e., order of reaction (n), and activation energy (E) The values of these parameters are important in the estimation of thermal stability TGA is used for studying the samples in the temperature range of 30e600C Based on the TGA curves all the films have shown three stages of weight loss It is evident that the initial weight loss for the pure PVA/MAA:EA blend sample starts from 30 to 130C with a weight loss of 7.8%, which may be due to the loss of entrapped water molecules and moisture The second weight loss occurs at 131e390C, which is attributed to melting temperature (Tm), it is around 344C This weight loss is attributed
to the degradation of the unsaturated groups of PVA The third weight loss starts from 391 to 472C with a weight loss of 21%
Fig 5 shows the dTGA curves of pure PVA/MAA:EA (50:50) blend and PVA/MAA:EA blendfilled with various weight fractions
of LiClO4filler As shown inFig 5(bed), all the doped films show three stages of degradation The initial weight loss for all the doped samples starts from 30 to 150C with the weight loss of 7e9%, which may be due to the evaporation of the residual solvent, moisture and impurities due to Chlorine compound (LiClO4) Beyond thefirst stage, the samples have a drastic weight loss in the temperature range 151e380C with the weight loss of 30e60%, which is assigned to melting temperature (Tm) The melting tem-perature of all the LiClO4dopedfilms exhibits decreasing nature as LiClO4content increases in the polymer matrix This result in the increase in the amorphous nature of the polymer blend electrolyte films The melting temperatures and decomposition temperatures
of pure and LiClO4doped polymer blend electrolytefilms are pre-sented inTable 3 The second weight loss is ascribed to dehydro-chlorination of LiClO4 which leads to the volatilization of monomers and oligomers The degradation of MAA:EA and the elimination of the unsaturated functional group of PVA are the contributions forfinal weight loss, which starts from 381 to 470C.
In conclusion, among all the LiClO4 complexed polymer blend electrolytefilms, 15 wt% of LiClO4dopedfilm shows more amor-phous nature than 5 and 10 wt%
The activation energy (E) for the main thermal decomposition for TGA measurements of the present samples, which depend on
Table 1
Direct band and indirect band gap values for pure and LiClO 4 doped PVA/MAA:EA (50:50) polymer blend electrolyte films.
PVA/MAA:EA: LiClO 4 (wt%) sample composition Direct band gap (eV) Indirect band gap (eV)
Fig 4 FTIR spectra of (a) pure (50:50) and different concentrations (b) 5 wt%, (c) 10 wt%
films.
T Siddaiah et al / Journal of Science: Advanced Materials and Devices 3 (2018) 456e463 459
Trang 5the residual mass, can be calculated in general using the integral
equation of Coats and Redfern[30]
log
logð1 aÞ
T2
¼ logDRE
12RTE
where T is the absolute temperature, E is the activation energy in J/
mol, R is the universal gas constant (8.3136 J/mol K) andais the
fractional weight loss at that particular temperature is calculated as
a¼wi wt
wi wf
(6)
where wiis the initial weight, wtis the weight at a given
temper-ature and wfis thefinal weight of the sample For n ¼ 1, Eq.(1)
reduce to
log
logð1 aÞ
T2
¼ logDRE
12RT E
0:434 E
By plotting log½logð1 aÞ=T2 against 1000/T for each sample,
we obtain straight lines Then, the apparent activation energies are
determined from the slope of these lines using the following equation
Values of the apparent activation energy (E) of the samples are noted inTable 4
3.5 Scanning electron microscopy
A scanning electron microscope creates images of a sample by scanning it with a focused electron beam An electron beam in-teracts with electrons in a sample that generates various signals that can be detected, and that contains information about the morphology and composition of the sample surface The electrons
in the beam interact with the sample, producing various signals that can be used to obtain information about the surface topog-raphy, morphology and composition that makes it invaluable in a variety of science and industry applications[31]
SEM is also used to study compatibility between different components of polymer electrolytes by detecting phase separations and interfaces[32,33] Compatibility between the polymer mixture and inorganic additives has a great influence on the thermal, me-chanical and ionic properties of polymer electrolytes
Fig 6shows the SEM images of pure PVA, Pure MAA:EA and PVA/MAA:EA (50:50) blend without and with different concen-trations 5, 10 and 15 wt% of Lithium Perchlorate It can be seen from
Fig 6(a) that pure MAA:EA copolymer film shows the smooth surface, suggesting that MAA and EA molecules may disperse in the soft e segment phase with little influence on the microphase separation and mixing of the hard and soft segments[34] The SEM image of pure PVAfilm has no characteristics attributable to any crystalline morphology Hence the semicrystallinity of PVA dis-cussed earlier is likely to be submicroscopic in nature[35]
Fig 6(c) shows the SEM images of PVA/MAA:EA (50:50) polymer blend electrolyte The lateral branches correlate poorly with the length of the trunk of the dendrites The growth of a dendrite-like form, which is a collection of branched aggregate clusters has begun and lead to the formation of a condensed aggregated form of dendrites This suggests the presence of structural reorganizations
of polymer chains [36] Fig 6(def) shows the SEM images of different concentrations (5, 10 and 15 wt%) of LiClO4doped polymer blendfilms The morphology was uniform with different degrees of roughness The increase in the degrees of roughness with increased
Table 2
Assignments of the FTIR characterization bands of pure and LiClO 4 doped PVA/MAA:EA polymer blend electrolyte films.
Pure PVA/MAA:EA (50:50) PVA/MAA:EA: LiClO 4 sample
Wavenumber (cm1) Assignment Wavenumber (cm1) Assignment
1436 O e H and C e H bending 2925 C e H stretching of methylene group
1722 C ¼ O stretching 3085e3565 O e H stretching
3135e3531 O e H stretching of alcohols and phenols e e
Fig 5 dTGA thermograms of (a) pure (50:50) and different concentrations (b) 5 wt%,
(c) 10 wt% and (d) 15 wt% of LiClO 4 doped PVA/MAA:EA polymer blend electrolyte
films.
Table 3
Melting and decomposition temperatures of pure PVA/MAA:EA and PVA/MAA:EA: LiClO 4 composite polymer blend electrolyte films.
PVA/MAA:EA: LiClO 4 (wt%) Sample Melting temperature (T m ) (C) Decomposition temperature (T d ) (C)
T Siddaiah et al / Journal of Science: Advanced Materials and Devices 3 (2018) 456e463 460
Trang 6Liþion concentration indicates that the crystalline salt was broken
into small pieces and mixed into the polymer blend[11] The SEM of
the blendfilm filled with 5 wt% LiClO4depicts a small spherulite
shape, scattered and distributed randomly in an isolated form
throughout thefilm With an increase in the concentration of the
filler upto 10 wt%, the number of the spherulites considerably
in-creases This leads to the increase in the degree of roughness and
indicates the segregation of dopant in the host matrix As the
dopant concentration increases, the size of the spherulites
in-creases leading to the formation of isolated spherulites distributed
all over the volume of thefilm[37]
3.6 Electrical conductivity
The ionic conductivity of the polymer electrolytes mainly
de-pends on the actual concentration of conducting charge carriers
and their mobility Fig 7 shows the typical impedance plots of
(PVA/MAA:EA) polymer electrolyte doped with various
concen-trations of LiClO4at ambient temperature in the frequency range of
1 Hze5 MHz FromFig 7, one observed a semicircle in the
high-frequency region and a tilted straight line in the low-high-frequency
region The presence of a semicircle indicates the non-Debye
character of the sample[38], since the potential well of each site
through which the ion transfer takes place is not equal It is
widely accepted that the semicircle is due to the bulk
resis-tance and capaciresis-tance of the electric double layer formed at the
electrode/electrode interface [39] This offers an increasing impedance against the ion transfer with decreasing the frequency The linear region in the low-frequencies is due to the influence
Table 4
Activation energy of pure PVA/MAA:EA and PVA/MAA:EA: LiClO 4 Composite polymer blend electrolyte films.
PVA/MAA:EA: LiClO 4 (wt%) Sample Activation energy (E) (KJ/mol) Activation energy (E) (eV)
Fig 6 SEM images of (a) pure MAA:EA, (b) pure PVA, (c) pure (50:50) and different concentrations (d) 5 wt%, (e) 10 wt% and (f) 15 wt% of LiClO 4 doped PVA/MAA:EA polymer blend electrolyte films.
Fig 7 Impedance plots (Cole-Cole plots) for (a) pure (50:50) and different concen-trations (b) 5 wt%, (c) 10 wt% and (d) 15 wt% of LiClO 4 doped PVA/MAA:EA polymer
films.
T Siddaiah et al / Journal of Science: Advanced Materials and Devices 3 (2018) 456e463 461
Trang 7of blocking electrodes With a higher concentration of dopant, the
lines slightly approach the imaginary axis, which indicates the
establishment of a better contact with the electrode The ionic
conductivity of the solid polymer blend electrolytes was
calculated using the following equation
where t is the thickness of the polymer blend electrolyte, A is the
area of the blocking electrode and Rb is the bulk resistance of
polymer blend electrolyte It is evident from the cole-cole plots at
different dopant concentrations that the intercept of the semicircle
(bulk resistance) on the real axis tends towards lower values with
increasing the dopant concentration which indicates that the
conductivity increases with dopant concentration
Fig 8shows the conductivity values of PVA/MAA:EAþ LiClO4
complexes as a function of salt concentrations at ambient
tem-perature in the frequency range of 1 Hze5 MHz FromFig 8, it is
observed that the ionic conductivity increases with increasing LiClO4 content in the polymer blend electrolyte The maximum conductivity of 7.35 108 S/cm was obtained for the PVA/ MAA:EAþ LiClO4(42.5:42.5:15) system The conductivity values of different complexes at room temperature are summarized in
Table 5 The highest ionic conductivity at 15 wt% salt doping is attributed to the highest electrolyte uptake Notes that, the con-ductivity is related to the number of Liþion charge carriers (ni) and their mobility (mi) [40] The coordination interaction of oxygen atoms of MAA:EA with Liþcations of LiClO4salt results in an in-crease in mobile charge carriers and reduction in the crystallinity of the PVA/MAA:EA mixture This is responsible for the increase of ionic conductivity These interactions have also been observed by FTIR, XRD and SEM analysis
Fig 9shows the plots of the logarithm of conductivity as a function of the logarithm of frequency for all the samples at room temperature The spectrum consists of two distinguishable regions within the measured frequency range The low-frequency region describing electrode-electrode interfacial phenomena is ascribed to the space charge polarization at the blocking electrodes[41] The high-frequency region corresponding to the bulk relaxation phe-nomena disappears gradually for the electrolytes, having the salt concentration up to 15 wt% may be due to the increase in jump frequency of charge carriers The conductivity of polymer electro-lytes initially increases due to the increment of charge carriers being introduced into the complex As the salt concentration in-creases, the number of carrier ions of the complex increases upto a particular limit of the salt concentration Above this concentration there is a stronger ion-ion interaction which possibly prevents the polymer backbone's segmental motion and then causes a lowering
of the dc conductivity[42]
4 Conclusion The pure polymer blend (50PVA:50MAA:EA) electrolyte and Polymer blend (50PVA:50MAA:EA) electrolytes with different concentrations (5, 10 and 15 wt%) of LiClO4have been prepared by the solution casting technique using the double distilled water X-ray diffraction patterns show a decrease in the degree of crystalli-zation and cause an increase in the amorphous region The FTIR spectra show the position shifts as well as the intensity changes This indicates the considerable interaction between the polymer blend and LiClO4 The dTGA curve shows three different stages of weight loss, which are due to the loss of the adsorbed water, the decomposition of the side chain and the main chain The melting and decomposition temperatures exhibit a decreasing trend with increasing LiClO4content in the polymer blend, which indicates the increase in amorphous nature SEM images of the Liþion doped films revealed the presence of the structural rearrangement of polymer chains UVe Visible analysis revealed that the value of the optical band gap decreases as the LiClO4content increases in the polymer blend This indicates the formation of charge transfer complexes between the polymer blend and the filler The maximum conductivity of 7.35 108S/cm was obtained for the system PVA/MAA:EAþ LiClO (42.5:42.5:15) at room temperature
Fig 8 Conductivity vs salt concentration plots of (PVA/MAA:EA þ LiClO 4 ) polymer
blend electrolyte system at room temperature.
Table 5 The conductivity values of Pure and LiClO 4 doped (PVA/MAA:EA) Polymer blend electrolyte films at room temperature.
PVA/MAA:EA: LiClO 4 sample composition (wt%) Conductivity at 303 K (S/cm) 50.0: 50.0: 0 2.46 10 8
47.5: 47.5: 5 3.86 10 8
45.0: 45.0: 10 4.39 10 8
42.5: 42.5: 15 7.35 10 8
Fig 9 Frequency dependent conductivity at room temperature for (a) pure (50:50)
and different concentrations (b) 5 wt%, (c) 10 wt% and (d) 15 wt% of LiClO 4 doped PVA/
MAA:EA polymer blend electrolyte films.
T Siddaiah et al / Journal of Science: Advanced Materials and Devices 3 (2018) 456e463 462
Trang 8From all the characterization results, the 15 wt% of LiClO4doped
polymer blend electrolyte system exhibits the better
semi-conducting nature which is more suitable for fabricating solid-state
batteries and other electrochemical devices
Acknowledgments
The authors thank E Bhoje Gowd, Senior Scientist, Department
of Materials and Minerals, National Institute of Interdisciplinary
Science and Technology (NIIST), Thiruvanthapuram, Kerala, for his
constant encouragement and active cooperation to carry out the
work
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