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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.
Journal of Science: Advanced Materials and Devices (2018) 456e463 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Thermal, structural, optical and electrical properties of PVA/MAA:EA polymer blend filled with different concentrations of Lithium Perchlorate T Siddaiah a, Pravakar Ojha a, N.O Gopal a, Ch Ramu a, *, H Nagabhushana b a b Department of Physics, Vikrama Simhapuri University PG Centre, Kavali, 524201, India CNR Rao Centre for Advanced Materials Research, Tumkur University, Tumkur, 572103, India a r t i c l e i n f o a b s t r a c t Article history: Received 18 July 2018 Received in revised form 17 November 2018 Accepted 18 November 2018 Available online 27 November 2018 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 2q ¼ 19.5 decreased 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 UV e 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 the filler 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 LiClO4 filled PVA/MAA:EA, FTIR spectra showed disappearance of some bands with the change in their intensities as compared to pure PVA/MAA:EA film This indicated considerable interaction between the polymer blend and LiClO4 filler SEM images of the polymer blend films complexed with LiClO4 suggested the presence of a structural rearrangement of the polymer chains The electrical conductivity of the prepared films was measured using the impedance analyzer in the frequency range from Hz to MHz at room temperature It was observed that the conductivity increased with increase of the Liỵion concentration â 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/) Keywords: Polymer Lithium Perchlorate PVA/MAA:EA blend FTIR TGA X e ray SEM and optical energy 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] Liỵ ion 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] * Corresponding author E-mail address: chramu8@gmail.com (Ch Ramu) Peer review under responsibility of Vietnam National University, Hanoi 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 (PVA e PANI), (PVA e PAN), (PVP e 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), (Chitosan e PVA), (PVA e NyC), (PEMA e PVdF), (PVA e NaAlg) and its copolymers P(VDF e 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 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 (http://creativecommons.org/licenses/by/4.0/) T Siddaiah et al / Journal of Science: Advanced Materials and Devices (2018) 456e463 miscibility 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 microphase configuration can induce drastic changes in all the properties (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 preparations, recycling of polymers, packaging textiles and leather industries 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 advantages 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 composition 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 Liỵ to form polymer-salt complexes and hence produce ionic conduction Electron pairs are formed on oxygen atoms of C ¼ O and C e O e C groups of PVA and hydrogen atoms in MAA:EA copolymer [13] 457 0.02 between and 40 FTIR spectra of the prepared samples were recorded using a PerkineElmer FTIR spectrometer, over a wavenumber range 500e4000 cmÀ1 SEM images of the polymer blend electrolyte films were characterized by Hitachi (TM e 3000 and H e 8100) electron microscope with scanning attachment The optical absorption curves of the films 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 electrolyte films were studied using a Hitester 3532-50 LCR in the frequency range of Hze5 MHz 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, thin films, nanomaterials and solid objects Fig shows 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 2q ¼ 19.5 , 1.4 and 0.6 , which indicates the semi-crystalline nature of the PVA/MAA:EA polymer blend film [14] The first one has a clear crystalline peak at a scattering angle 2q ¼ 19.5 which corresponds to a (1 0) reflection [15] The present X-ray pattern revealed no significant changes in the positions of three peaks after complexation with filler, the intensity 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 Liỵ content 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 electrolyte systems The decrease in crystallinity with increasing LiClO4 content in the blended sample involves a decrease in the number of Experimental MAA: EA copolymer (1:1) dispersion of 30 percent is a dispersion 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 LiClO4 complexed films 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 LiClO4 were 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 doped films at the bottom of the dishes The thermal properties of the prepared samples were studied using SEIKO thermal analysis system (TGA e 20) in the presence of nitrogen flow from 40 to 700 C, at the heating rate of 10 C/min The X-ray diffraction patterns were performed using a Siemens D5000 diffractometer with CuKa radiation (l ¼ 1.5406 Å) The prepared films were scanned at 2q angles with a step size of Fig XRD patterns of (a) pure (50:50) and different concentrations (b) wt% (c) 10 wt% and (d) 15 wt% of LiClO4 doped PVA/MAA:EA polymer blend films 458 T Siddaiah et al / Journal of Science: Advanced Materials and Devices (2018) 456e463 hydrogen bonds formed between PVA and MAA: EA The peak at 2q ¼ 19.5 has been found to increase in broadness and decrease in intensity as Liỵ ion content increases and enhances the complexation 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 intensity of the diffraction pattern decreases as the amorphous nature increases by the addition of a dopant In the present work, no sharp peaks were observed for higher concentrations of LiClO4 salt 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 a flexible 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 coefficientaị ẳ 2:303 Â A d (1) Fig The plot of (ahy)2 vs (hy) of (a) pure (50:50) and different concentrations (b) wt%, (c) 10 wt% and (d) 15 wt% of LiClO4 doped PVA/MAA:EA polymer blend electrolyte films where A is the absorbance and d is the thickness of the films 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 prepared films was estimated by using Tauc's relationship [22], n ahyị ẳ B hy Eg (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 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 hy À Egd À ahy¼ B2 hy À Egi 1=2 Á2 (3) (4) where Egd and Egi are the direct and indirect band gaps, respectively, B1 and B2 are constants Figs and represent the plots of (ahy)2 and (ahy)1/2 versus photon energy (hy) for pure and different weight fractions (5, 10 and 15 wt%) of LiClO4 doped PVA/MAA:EA polymer blend electrolyte films The direct and indirect band gap values are determined by extrapolating the linear part of the curves (ahy)2 and (ahy)1/2 versus photon energy (hy) to zero absorption value The evaluated band gap values (both direct and indirect) are reported in Table From Table 1, it is clear that both direct and indirect energy band gap values decrease with increasing in the LiClO4 content in the polymer blend The doped LiClO4 salt increases the disorder of the Fig The plot of (ahy)1/2 vs (hy) of (a) pure (50:50) and different concentrations (b) wt%, (c) 10 wt% and (d) 15 wt% of LiClO4 doped PVA/MAA:EA polymer blend electrolyte films 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 energy band gap and indirect energy band gap value Hence it has more semiconducting nature than remaining PVA complexed polymer blend electrolyte films [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 T Siddaiah et al / Journal of Science: Advanced Materials and Devices (2018) 456e463 459 Table Direct band and indirect band gap values for pure and LiClO4 doped PVA/MAA:EA (50:50) polymer blend electrolyte films PVA/MAA:EA: LiClO4 (wt%) sample composition Direct band gap (eV) Indirect band gap (eV) 50: 50: 47.5: 47.5: 45: 45: 10 42.5: 42.5: 15 5.04 4.90 4.68 4.04 4.36 3.91 3.82 3.66 formation of hydrogen bonds [24] Fig 4(aed) shows FTIR transmittance spectra of PVA/MAA:EA (50:50) blend without and with different concentrations 5, 10 and 15 wt % of LiClO4 recorded at room temperature in the region 500e4000 cmÀ1 FTIR transmittance band positions and their corresponding assignments are presented in Table for all prepared composite films Fig 4(a) shows the FTIR spectrum of pure PVA/MAA:EA blend The bands at about 3135e3531 and 1436 cmÀ1 belong to the stretching and bending vibration of the hydroxyl group, respectively [25] The band characterized for the methylene group (CH2) asymmetric stretching vibration occurs at about 2934 cmÀ1 The band at about 1099 cmÀ1 corresponds to C e O stretching of acetyl groups present on the PVA backbone [16,26] The vibrational band at about 1722 cmÀ1 is assigned to C ¼ 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 cmÀ1 for 5, 10 and 15 wt% of LiClO4 complexed films, respectively, arises from O e H stretching frequency and is an indication 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 cmÀ1 for pure blend are found to be absent in Liỵ ion doped blend lms The disappearance of bands observed in blend lm with Liỵ ion doping suggests the co-ordination or complexation of chlorine with the blend film [27] Fig FTIR spectra of (a) pure (50:50) and different concentrations (b) wt%, (c) 10 wt% and (d) 15 wt% of LiClO4 doped PVA/MAA:EA polymer blend electrolyte films It was found that a small absorption band around 922 cmÀ1 is 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 blend film, but it disappeared in the spectra of the Liỵ ion 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 begins, then decreases rapidly over a comparatively narrow temperature range and finally 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 30e600 C 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 130 C 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 131e390 C, which is attributed to melting temperature (Tm), it is around 344 C This weight loss is attributed to the degradation of the unsaturated groups of PVA The third weight loss starts from 391 to 472 C with a weight loss of 21% Fig shows the dTGA curves of pure PVA/MAA:EA (50:50) blend and PVA/MAA:EA blend filled with various weight fractions of LiClO4 filler As shown in Fig 5(bed), all the doped films show three stages of degradation The initial weight loss for all the doped samples starts from 30 to 150 C 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 the first stage, the samples have a drastic weight loss in the temperature range 151e380 C with the weight loss of 30e60%, which is assigned to melting temperature (Tm) The melting temperature of all the LiClO4 doped films exhibits decreasing nature as LiClO4 content 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 LiClO4 doped polymer blend electrolyte films are presented in Table The second weight loss is ascribed to dehydrochlorination 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 for final weight loss, which starts from 381 to 470 C In conclusion, among all the LiClO4 complexed polymer blend electrolyte films, 15 wt% of LiClO4 doped film shows more amorphous nature than and 10 wt% The activation energy (E) for the main thermal decomposition for TGA measurements of the present samples, which depend on 460 T Siddaiah et al / Journal of Science: Advanced Materials and Devices (2018) 456e463 Table Assignments of the FTIR characterization bands of pure and LiClO4 doped PVA/MAA:EA polymer blend electrolyte films PVA/MAA:EA: LiClO4 sample Pure PVA/MAA:EA (50:50) Wavenumber (cmÀ1) Assignment Wavenumber (cmÀ1) Assignment 847 922 1099 1436 1722 2934 3135e3531 CH2 rocking C e O stretching C e O stretching O e H and C e H bending C ¼ O stretching CH2 Asymmetric stretching O e H stretching of alcohols and phenols 839 922 1722 2925 3085e3565 e e C ¼ C stretching C e O stretching C ¼ O stretching C e H stretching of methylene group O e H stretching e e determined from the slope of these lines using the following equation E ¼ 2:303R Â slope (8) Values of the apparent activation energy (E) of the samples are noted in Table 3.5 Scanning electron microscopy Fig dTGA thermograms of (a) pure (50:50) and different concentrations (b) wt%, (c) 10 wt% and (d) 15 wt% of LiClO4 doped PVA/MAA:EA polymer blend electrolyte films the residual mass, can be calculated in general using the integral equation of Coats and Redfern [30] % $ # " Àlogð1 À aÞ R 2RT E À À ¼ log log E 2:304R DE T2 (5) 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) and a is the fractional weight loss at that particular temperature is calculated as a¼ wi À wt wi À wf (6) where wi is the initial weight, wt is the weight at a given temperature and wf is the final weight of the sample For n ¼ 1, Eq (1) reduce to % $ # " Àlogð1 À aÞ R 2RT E À 0:434 1À ¼ log log E RT DE T (7) By plotting logẵlog1 aị=T against 1000/T for each sample, we obtain straight lines Then, the apparent activation energies are A scanning electron microscope creates images of a sample by scanning it with a focused electron beam An electron beam interacts 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 topography, 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, mechanical and ionic properties of polymer electrolytes Fig shows the SEM images of pure PVA, Pure MAA:EA and PVA/MAA:EA (50:50) blend without and with different concentrations 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 PVA film has no characteristics attributable to any crystalline morphology Hence the semicrystallinity of PVA discussed 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 LiClO4 doped polymer blend films The morphology was uniform with different degrees of roughness The increase in the degrees of roughness with increased Table Melting and decomposition temperatures of pure PVA/MAA:EA and PVA/MAA:EA: LiClO4 composite polymer blend electrolyte films PVA/MAA:EA: LiClO4 (wt%) Sample Melting temperature (Tm) ( C) Decomposition temperature (Td) ( C) 50:50:0 47.5:47.5:5 45:45:10 42.5:42.5:15 344 317 311 292 424 418 413 410 T Siddaiah et al / Journal of Science: Advanced Materials and Devices (2018) 456e463 461 Table Activation energy of pure PVA/MAA:EA and PVA/MAA:EA: LiClO4 Composite polymer blend electrolyte films PVA/MAA:EA: LiClO4 (wt%) Sample Activation energy (E) (KJ/mol) Activation energy (E) (eV) 50:50:0 47.5:47.5:5 45:45:10 42.5:42.5:15 88.45 84.23 82.78 77.34 1.46 1.39 1.37 1.28 Fig SEM images of (a) pure MAA:EA, (b) pure PVA, (c) pure (50:50) and different concentrations (d) wt%, (e) 10 wt% and (f) 15 wt% of LiClO4 doped PVA/MAA:EA polymer blend electrolyte lms Liỵ ion concentration indicates that the crystalline salt was broken into small pieces and mixed into the polymer blend [11] The SEM of the blend film filled with wt% LiClO4 depicts a small spherulite shape, scattered and distributed randomly in an isolated form throughout the film With an increase in the concentration of the filler upto 10 wt%, the number of the spherulites considerably increases 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 increases leading to the formation of isolated spherulites distributed all over the volume of the film [37] 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 3.6 Electrical conductivity The ionic conductivity of the polymer electrolytes mainly depends on the actual concentration of conducting charge carriers and their mobility Fig shows the typical impedance plots of (PVA/MAA:EA) polymer electrolyte doped with various concentrations of LiClO4 at ambient temperature in the frequency range of Hze5 MHz From Fig 7, one observed a semicircle in the highfrequency region and a tilted straight line in the low-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 resistance and capacitance of the electric double layer formed at the Fig Impedance plots (Cole-Cole plots) for (a) pure (50:50) and different concentrations (b) wt%, (c) 10 wt% and (d) 15 wt% of LiClO4 doped PVA/MAA:EA polymer blend electrolyte films 462 T Siddaiah et al / Journal of Science: Advanced Materials and Devices (2018) 456e463 of 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 s ¼ t=Rb A (9) 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 shows the conductivity values of PVA/MAA:EA ỵ LiClO4 complexes as a function of salt concentrations at ambient temperature in the frequency range of Hze5 MHz From Fig 8, it is Fig Conductivity vs salt concentration plots of (PVA/MAA:EA ỵ LiClO4) polymer blend electrolyte system at room temperature Fig Frequency dependent conductivity at room temperature for (a) pure (50:50) and different concentrations (b) wt%, (c) 10 wt% and (d) 15 wt% of LiClO4 doped PVA/ MAA:EA polymer blend electrolyte films Table The conductivity values of Pure and LiClO4 doped (PVA/MAA:EA) Polymer blend electrolyte films at room temperature PVA/MAA:EA: LiClO4 sample composition (wt%) Conductivity at 303 K (S/cm) 50.0: 47.5: 45.0: 42.5: 2.46 3.86 4.39 7.35 50.0: 47.5: 45.0: 42.5: 10 15 Â Â Â Â 10À8 10À8 10À8 10À8 observed that the ionic conductivity increases with increasing LiClO4 content in the polymer blend electrolyte The maximum conductivity of 7.35 Â 10À8 S/cm was obtained for the PVA/ MAA:EA ỵ LiClO4 (42.5:42.5:15) system The conductivity values of different complexes at room temperature are summarized in Table The highest ionic conductivity at 15 wt% salt doping is attributed to the highest electrolyte uptake Notes that, the conductivity is related to the number of Liỵ ion charge carriers (ni) and their mobility (mi) [40] The coordination interaction of oxygen atoms of MAA:EA with Liỵ cations of LiClO4 salt results in an increase 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 shows 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 phenomena 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 electrolytes initially increases due to the increment of charge carriers being introduced into the complex As the salt concentration increases, 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] 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 LiClO4 have been prepared by the solution casting technique using the double distilled water Xray diffraction patterns show a decrease in the degree of crystallization 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 LiClO4 content in the polymer blend, which indicates the increase in amorphous nature SEM images of the Liỵ ion doped lms revealed the presence of the structural rearrangement of polymer chains UV e Visible analysis revealed that the value of the optical band gap decreases as the LiClO4 content 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 Â 10À8 S/cm was obtained for the system PVA/MAA:EA ỵ LiClO4 (42.5:42.5:15) at room temperature T Siddaiah et al / Journal of Science: Advanced Materials and Devices (2018) 456e463 From all the characterization results, the 15 wt% of LiClO4 doped polymer blend electrolyte system exhibits the better semiconducting nature which is more suitable for fabricating solid-state batteries and other electrochemical devices [21] Acknowledgments [22] 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 [20] [23] [24] [25] [26] References 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