Optical, Electrical and Viscosity Properties of Poly

International Research Journal of Pure & Applied Chemistry 9(4): 1-13, 2015, Article no.IRJPAC.19118 ISSN: 2231-3443

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Optical, Electrical and Viscosity Properties of Poly (Vinyl Alcohol) Films Embedded with Cr2O3 Nanoparticles Synthesised by Biological and Electrochemical Methods Rakesh1, Sowbhagya1, Sannaiah Ananda1* and Netkal M. Made Gowda2 1

Department of Studies in Chemistry, University of Mysore, Manasagangothri, Mysore-570006, India. 2 Department of Chemistry, Western Illinois University, One University Circle, Macomb- 61455, USA. Authors’ contributions This work was carried out in collaboration between all authors. Author SA designed the study and wrote the protocol. Author Rakesh preformed the experiments, statistical analysis, managed the literature search and wrote the first draft of the manuscript with assistance from author Sowbhagya. Authors SA and NMMG read and approved the final manuscript. Article Information DOI: 10.9734/IRJPAC/2015/19118 Editor(s): (1) Edmond Dik-Lung Ma, Department of Chemistry, Hong Kong Baptist University, Hong Kong, China. Reviewers: (1) Dinesh K. Kanchan, University of Baroda, Vadodara, India. (2) Anonymous, Wrocław University of Technology, Poland. (3) Önder Pekcan, Kadir Has University, Turkey. (4) Anonymous, The University of Southern Mississippi, USA. Complete Peer review History: http://sciencedomain.org/review-history/11217

Original Research Article

Received 26th May 2015 th Accepted 14 August 2015 st Published 1 September 2015

ABSTRACT The effect of Cr2O3 nanoparticles embedded in PVA on the structural, electrical and optical properties of composite films is studied experimentally. Sample is PVA films embedded with different sizes and concentrations of Cr2O3 nanoparticles. Structural properties are studied using Xray diffraction, SEM, and FTIR spectrum. Optical property is studied using UV-Visible spectroscopy. Results show that by embedding Cr2O3 nanoparticles in PVA, number of Bragg’s planes in the structure of polymer and its crystallinity are increased noticeably. The λmax of Cr2O3 undergoes a blue shift towards the lower wavelength after embedding. Scanning electron microscopy shows that the prepared Cr2O3 nanoparticles were dispersed and nearly uniform in diameter within the _____________________________________________________________________________________________________ *Corresponding author: E-mail: [email protected];

Rakesh et al.; IRJPAC, 9(4): 1-13, 2015; Article no.IRJPAC.19118

polymeric matrix. Frequency dependent conductivity, photo-voltaic activity and viscosity measurements of PVA and PVA-Cr2O3 nanoparticles composites films/solutions are also discussed. The induced structural changes, revealed through XRD and FTIR spectroscopy, are responsible for the observed changes in optical behaviour of PVA after embedding Cr2O3 nanoparticles in it. Keywords: Cr2O3 nanoparticles; nanocomposite films.

chromium

doped

platinum

electrode

(Pt/Cr);

Cr2O3-PVA

absence of uncontrolled by-products [23]. Systematic studies related to the effect of embedding Cr2O3 nanoparticles on the optical and electrical behaviour of the PVA matrix are scare. A, Hassan et al., has reported the synthesis of nano-sized Cr2O3 by sol-gel method and mixed with PVA to produce nanocomposites films.DSC studies of these films showed the thermal stability and degree of crystallinity of the PVA were reinforced by the addition of Cr2O3 nanoparticles [24]. In this endeavour, we have carried out a systematic study on the effect of embedding of different concentration of Cr2O3 nanoparticles on optical and electrical properties.

1. INTRODUCTION Metal and metal oxide nanoparticles [1-3] combined polymers have attracted widened application by these hybrid materials [4]. It is well established that certain polymers, as dielectric materials, are excellent host matrices for encapsulation of metal nanoparticles like silver, gold, copper, and so forth, as they act both as reducing as well as capping agents and also provide environmental and chemical stability [5-7]. At the same time, these embedded nanoparticles inside the polymer matrix also affect the properties of the host itself [8-11]. Particularly, polymer-metal-nanoparticles composites are promising functional materials in several fields such as optical, electrical, thermal, mechanical, and antimicrobial properties [12-16]. Many reports in the literature [17-18] show attempts for synthesis of metal nanoparticles based polymer nanocomposites, with the possibility of variation in their optical and electrical properties for their application in high performance capacitors, conductive inks, and other electronic components. For their application in optoelectronic, electrical, and optical devices, biomedical science, and sensors, main key points are selection of polymer-metal nanoparticles combination, controlling the particles size, their concentration, and distribution within the polymer matrix [19-21].

2. EXPERIMENTAL Cr2O3 nanoparticles were synthesized by three different methods in our laboratoryand published [1-3]. In continuation of this Cr2O3/PVA nanocomposite films were prepared as follows.

2.1 Method 1 Includes the addition of potassium dichromate solution to the plant extract in a beaker and stirred for 10-15min. The colour of the solution changed from orange to green indicating the formation of chromium (III) oxide nanoparticles. The solution was kept at room temp for evaporation of aqueous phase. The green solid product was dried in hot air oven at 65ºC-70ºC for an hour. The resulting solid was calcined at 650ºC-700ºC for 3hrs. The addition of potassium dichromate solution to the plant extract containing mild reducing agents causes the reduction of orange dichromate (VI) ions to green chromium (III) ions. As an example, the reduction of Cr6+ to Cr3+ by reducing sugars resulting in the formation of Cr2O3 nanoparticles is shown in scheme 1.

In this paper, we have reported the preperation of poly (vinyl alcohol)-Cr2O3nanocomposites. PVA is water soluble, easily processable, having good film forming and adhesive nature for applications in optical coating and opto-electronic devices. Further, it is also considered as a good host matrix for metal nanoparticles [22]. It is also recognized as one of the very few vinyl polymers soluble in water with a high transparency, excellent thermal stability, chemical resistance, high mechanical strength, moderate, dopant dependent electrical conductivity and good flexibility. A remarkable and advantageous feature of nanoparticles prepared using these techniques in contrast to those prepared using chemical synthesis is smaller in particle size and

2-

+

3RCHO + Cr2O7 + 8H → 3RCOOH + 2Cr + 4H2O

3+

Scheme 1. Probable mechanism for the synthesis of Cr2O3 by method 1

2


2.2 Method 2

2.4 Preperation of PVANanocomposite Films

Cr2O3 nanoparticles are synthesized electrochemically using platinum electrodes. A solution of potassium dichromate (0.3 M) is prepared. The electrochemical cell consists of reaction chamber, voltage power supply and platinum electrodes. The experiment is performed with 20 ml volume of potassium dichromate solution along with 5.0 ml of conc. H2SO4 as a supporting medium. A positive voltage of 12 V is applied using battery eliminator (Neulite India) and current output of 70 mA-90 mA. The experiment is run for 3hrs with continuous stirring. A change in colour from orange to dark green is observed. The above solution is allowed for the slow evaporation in a hot air oven at 100ºC for 2hrs. Further, the solid is calcined at 650ºC-700ºC for removal of moisture and sulphate as sulphur dioxide as shown in scheme 2.

Cr2O3

PVA-Cr2O3 nanocomposite films with varying concentration (0.125%, 0.25% and 0.5%) of Cr2O3 nanoparticles are prepared by mixing different amounts of prepared Cr2O3from above mentioned different methods to PVA solution. For this purpose, 1% of PVA solution was prepared in de-ionized water and then different amount of Cr2O3 are added under continuous stirring for an hour, at 500 rpm followed by ultrasonication. In order to convert the PVA and its nanocomposite solutions with different concentration of Cr2O3 (wt %) into films, the respective solution was casted to the plastic petri-dish. After evaporation of solvent at ambient temperature for 24 hrs in the closed atmosphere. The film was peeled off and rinsed in benzene to remove any volatile material. Cr

2K2Cr2O7 + 8H2SO4 → 2K2SO4 +2Cr2 (SO4)3 + 3O2 +8H2O 4Cr2 (SO4)3 → 4Cr2O3 + 12SO2 + 6O2

3NaHCO3 + 3eCr3+ + 3OH-


Cr3+ + 3e3CO2 + 3Na + 3OHCr(OH)3

4Cr3+ + 6OH2Cr(OH)3

2.3 Method 3

2Cr2O3 + 3H2 Cr2O3 + 3H2O


In this method a thin film of chromium is deposited electrochemically on a platinum electrode (Pt/Cr) from chromium nitrate solution (0.1 M). The preparation of Cr2O3 nanoparticles carried in a reaction chamber containing 20 ml of NaHCO3 solution. Voltage power supply of 12 V, current of 30 mA and Pt/Cr electrode as anode, Pt electrode as cathode are used. The experiment is run for 3 hrs with continuous stirring at constant temperature. The anodic dissolution of chromium to give Cr3+ ions due to electrolytic reaction, which are electrochemically 3+ reacted with aqueous NaHCO3 to form Cr oxides/ hydroxides, The product formed floats in the electrolyte solution the resulting gel was filtered, washed several times with distilled water till complete removal of unreacted NaHCO3 and dried at 100ºC for dehydration and removal of hydroxides. The dried compound is calcined for 3 hrs at 650ºC-700ºC in muffle furnace in order to decompose the hydroxides of chromium and to get chromium (III) oxide. The electrochemical reaction takes place according to the following mechanism shown in scheme 3.

3. RESULTS AND DISCUSSION 3.1 Optical Characterization The UV/Vis absorption spectra are measured in the wavelength region of 190-1100 nm using spectrophotometer (Shimadzu-1700 series). Fig. 1 represents the optical absorption spectra obtained for pure PVA and its composites at varying concentrations of Cr2O3 nanoparticles. For pure PVA (curve a) there is a small absorption peak at 276 nm, which may be attributed to the n-π* transition of the C=O group of PVA [25] while it remains transparent in the complete visible region. For PVA- Cr2O3 nanocomposite films(curve b, c and d), in addition to this small peak, another absorption band having peak position at 360 nm starts emerging with its intensity increasing continuously with an increase in the content of Cr2O3 nanoparticles embedded in PVA. This band corresponds to the absorption of embedded

3


Cr2O3 nanoparticles. The optical absorption edges of the nanocomposite films are shifted towards the shorter wavelength region from 430 to 360 nm [1]. This blue shift in the optical absorption edge indicates the existence of Cr2O3 particles in the PVA matrix in the nanometer regime [26].

3.2 Fourier Transform Spectroscopy

3.3 X-ray Diffraction Studies Crystallographic interpretations are performed by X-ray diffractometer (Panalytical X-pert) using Cu kα wavelength (λ = 1.5406) and scanning range from 0º to 100º. Fig. 3 represents the XRD pattern for pure PVA and PVA- Cr2O3 nanocomposite film with varying concentration (0.125%, 0.25% and 0.5%) of Cr2O3 nanoparticles. The diffraction pattern of pure PVA (curve a) indicates a diffraction band around 2θ=20º. It is evident from this figure, that the relative intensity of this peak decreases after the embedding of Cr2O3 nanoparticles in PVA matrix, and new peaks at 2θ values of 24.6º, 36.3º, 50.2º and 63.6º correspond to the crystal plane of (012), (110), (024) and (214) of crystalline Cr2O3 [1] start emerging at 0.5% doping of Cr2O3 with increased intensities as a result of increasing concentration of embedded Cr2O3 nanoparticles. The appearance of charactestic peaks justifies the existence of Cr2O3 nanoparticles in the amorphous phase of PVA.

Infra-Red

FT-IR absorption spectra are carried out using the single beam Fourier transform-infrared spectrometer (Bruker Tensor 27-43875) consisting of ATR (Attenuated total reflectance) unit. Fig. 2 represents the FTIR spectra of pure PVA (spectrum a) and PVA-Cr2O3 (spectrum b, c and d) nanocomposite films in the wave number -1 range 400-4000 cm . All spectra exhibit the characteristic absorption bands of pure PVA -1 which are 3450, 2974, 1570, 1460 and 845 cm [27]. It can be noticed that upon doping of nanocomposites cause some remarkable changes in the spectral features of the samples in the fingerprint region (1100-500 cm-1), apart from new absorption bands and slight changes in the intensities of some absorption bands. The vibrational peaks at 3450, 2974, 1570, 1460 and 845 cm-1 are assigned to O-H stretching, C-H stretching, C=O stretching, C-H bend of CH2, and CH rocking of PVA respectively [28,29]. Further, the vibrational peaks found in the range 967-1 -1 1037cm are attributed to Cr=O, 585-641 cm -1 are attributed to Cr-O and 1046-1085 cm are attributed to Cr-O-Cr vibrations [1]. Fig. 2 indicates an increase in the vibrational intensity of O-H, C-H and C=O groups in the PVA matrix after addition of Cr2O3 nanoparticles directly in the PVA film.

3.4 Scanning Electron Microscopy (SEM) Scanning electron microscopy (ZESIS) is used to study the surface morphology of polymeric films before and after doping with Cr2O3 nanoparticles with different filling level. Fig. 4a represents the morphology and surface nature of PVA film prepared by solution casting technique. Figs. 4b, 4c and 4d show SEM images of Cr2O3 nanoparticles filled PVA films. The nanoparticles from all formulation displayed nearly spherical shapes with agglomeration.

Fig. 1. Optical absorption spectrum of PVA- Cr2O3 nanocomposite films with (a) PVA, (b) 0.125%, (c) 0.25% and (d) 0.5% amount Cr2O3 nanoparticles 4


Fig. 2. FTIR spectrum of PVA pure film and Cr2O3 nanoparticles doped in PVA polymer films in the wave number 400-4000 cm-1

Fig. 3. X-ray diffraction of PVA polymer and Cr2O3 nanoparticle doped PVA films; (a) PVA, (b) 0.125%, (c) 0.25%, and (d) 0.5% frequencies 50 Hz and 1000 Hz. The plot of conductivity as a function of frequency and concentration, for PVA and Cr2O3 nanoparticles embedded PVA films of different concentrations at room temperature is shown in Figs. (7a-7c). It can be observed that AC conductivity show low frequency dispersion with a decrease in conductivity at higher frequency. The low frequency dispersive region is due to electrode polarization effects at the electrode-electrolyte interface. As the frequency decreases more and more charge accumulation occurs at the electrode electrolyte interface which leads to the decrease in the number of mobile ions and hence conductivity revealing the non-Debye behaviour of the polymer system [31].

3.5 Viscosity Measurements The solution viscosity of pure PVA and PVACr2O3 nanocomposite of different concentration prepared from three different methods are determined by Ostwald viscometer. This viscometer is a simple glass capillary device and care has been taken to see that all the measurements are made using constant volume of the solution [30]. The viscosity data indicates that the increase in volume of the polymer matrix as the concentration of Cr2O3 nanoparticles increases and hence restricts molecular mobility of the polymer solution. A representative graph for the determination of intrinsic viscosity for PVA-Cr2O3 nanocomposite solution of method 3 is shown in the Figs. (6a-6c). The data and plots are shown in table (1) and Fig. 5.

3.7 Photo-voltaic Activity Conductivity and potential measurements were performed for PVA and PVACr2O3 nanocomposite films at different concentrations and compared the same under UV, sunlight and dark conditions. The photo-voltaic activity for PVA- Cr2O3 nanocomposite films is enhanced to an appreciable extent in presence of UV-light

3.6 Frequency-dependent Conductivity AC conductivity of the PVA and Cr2O3 nanoparticles embedded PVA films are measured using conductivity bridge instrument at 5

Rakesh et al.; IRJPAC, 9(4): 1-13,, 2015; Article no.IRJPAC.19118 no.IRJPAC.

than the sunlight and dark conditions. It can be attributed due to the λmax of Cr2O3 nanoparticles has under gone blue shift from 430 nm to 360 nm

after embedding into PVA matrix, hence it is UV active. Which is shown in Figss. (8a-8c) and (9a-9c).

4a

4b

4c 4d Fig. 4(a-d). Scanning electron micrograph of PVA and Cr2O3 nanoparticles filled PVA films

Intrensic viscosity [η]

175 155 135 115 95

Method 1 Method 2 Method 3

75 55 35 0.0119

0.0219

Conc0.0319 of Cr2O3

0.0419

Fig. 5. Plot of intrinsic viscosity [η] versus Concentration of Cr2O3 nanocomposites samples of methods 1, method 2 and method 3

6


38.4

ηsp/C or ln ηr/C

38.2 38 ηsp/C ln ηr/C

37.8 37.6 37.4 37.2 37 0

0.0002

0.0004

0.0006

0.0008 0.001 concentration

0.0012

0.0014

0.0016

0.0018

ηsp/C or lnηr/C

Fig. 6a. Plots of ηsp/C versus C and lnηr/C versus C for PVA- Cr2O3 nanocomposite samples of method 3 with 0.0119 g/dl of Cr2O3 nanoparticles 85 84 83 82 81 80 79 78

ηsp/C ln ηr/C

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0.0018

concentration

ηsp/C or ln ηr/C

Fig. 6b. Plots of ηsp/C versus C and lnηr/C versus C for PVA- Cr2O3 nanocomposite samples of method 3 with 0.0238 g/dl of Cr2O3 nanoparticles 126 124 122 120 118 116 114 112

ηsp/C ln ηr/C

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0.0018

concentration

Fig. 6c. Plots of ηsp/C versus C and lnηr/C versus C for PVA- Cr2O3 nanocomposite samples of method 3 with 0.075 g/dl of Cr2O3 nanoparticles 7


6

4.5

PVA ac conductivity

4 conductance

PVA+Cr2O 3(0.125%) PVA+Cr2O 3(0.25%) PVA+Cr2O 3(0.5%)

3.5 3

50 Hz

2.5

1000 Hz

2

1 1.5

2

2.5

3

0

3.5

0.1

logf


0.4

0.5

Fig. 7a. Plots of AC conductivity versus log f and conductance versus concentration for PVA and different PVA- Cr2O3 nanocomposite films prepared from method 1 7

5

PVA

4.5

5

3

conductance

ac conductivity


4 3.5 3 2.5

1 1.5

2

2.5

3

50 Hz 1000 Hz

2

3.5

0

0.1

logf


0.4

0.5

Fig. 7b. Plots of AC conductivity versus log f and conductance versus concentration for PVA and different PVA- Cr2O3 nanocomposite films prepared from method 2 6

5

PVA 5

4.5

4 3

conductance

ac conductivity


2

4 3.5 50 Hz

3

1000 Hz

2.5 2

1 1.5

2.5 logf

0

3.5

0.1


0.4

0.5

Fig. 7c. Plots of AC conductivity versus log f and conductance versus concentration for PVA and different PVA- Cr2O3 nanocomposite films prepared from method 3

8


Conductivity μs

2.5 2 1.5 UV light Sunlight Dark

1 0.5 0 1

2

3

Fig. 8a. Conductivity measurements of PVAPVA Cr2O3 nanocomposite films of 1. (0.125%) 2. (0.25%) and 3. (0.5%) prepared from method 1

Conductivity μs

2.5 2 1.5 UV light

1

Sunlight

0.5 Dark

0 1

2

3

Fig. 8b. Conductivity measurements of PVAPVA Cr2O3 nanocomposite films of 1. (0.125%) 2. (0.25%) and 3. (0.5%) prepared from method 2

Conductivity μs

4 3 2

UV light

1

Sunlight Dark

0 1

2

3

Fig. 8c. Conductivity measurements of PVAPVA Cr2O3 nanocomposite films of 1. (0.125%) 2. (0.25%) and 3. (0.5%) prepared from method 3

9


Potential(mV)

0.2 0.15 0.1

UV light Sunlight

0.05 Dark

0 1

2

3

Fig. 9a. Potential measurements of PVAPVA Cr2O3 nanocomposite films of 1. (0.125%) 2. (0.25%) and 3. (0.5%) prepared from method 1

Potential(mV)

0.2 0.15 0.1 UV light 0.05

Sunlight Dark

0 1

2

3

Fig. 9b. Potential measurements of PVAPVA Cr2O3 nanocomposite films of 1. (0.125%) 2. (0.25%) and 3. (0.5%) prepared from method 2

Potential(mV)

0.2 0.15 0.1 UV light 0.05

Sunlight Dark

0 1

2

3

Fig. 9c. Potential measurements of PVAPVA Cr2O3 nanocomposite films of 1. (0.125%) 2. (0.25%) and 3. (0.5%) prepared from method 3 10


Table 1. Viscosity data for PVA- Cr2O3 nanocomposite samples with different concentration of Cr2O3, prepared by method 1 Concentration of Cr2O3 C(g/dl)

0.0119

0.0238

0.0475

Concentration of PVA

Flow time, t (sec)

Relative viscosity t/t0=ηr

Specific viscosity ηr-1= ηsp

Reduced viscosity ηsp/C

lnηr

Inherent viscosity lnηr/C

0.0008 0.0012 0.0016 0.0008 0.0012 0.0016 0.0008 0.0012 0.0016

146.17 155.98 166.36 150.10 162.29 175.41 155.00 170.14 186.72

1.0592 1.0892 1.1195 1.0876 1.1333 1.1804 1.1231 1.1881 1.2565

0.0592 0.0892 0.1195 0.0876 0.1333 0.1804 0.1231 0.1881 0.2565

74.00 74.33 74.68 109.50 111.08 112.75 153.87 156.75 160.31

0.0575 0.0854 0.1128 0.0839 0.1251 0.1658 0.1160 0.1723 0.0228

71.87 71.16 70.50 104.87 104.25 103.62 145.00 143.58 142.68

11

Intrinsic viscosity [η](dl/g)

73.25

106.20

147.20


4. CONCLUSION 6.

Solid polymer films of polyvinyl alcohol (PVA) embedded with different weight percentage of Cr2O3 are prepared by three different methods using solution cast technique. FTIR spectrum peaks correspond to molecular vibrations and chemical bonds, indicate the presence of Cr2O3 in the PVA polymer structure. The λmax of Cr2O3 nanoparticles undergo Blue shift from 430nm to 360nm after doping to PVA polymer. The electrical conductivity and intrinsic viscosity of PVA- Cr2O3 nanocomposite films have been found to increase with increase in nanoparticles concentration at room temperature.

7.

8.

COMPETING INTERESTS 9.

Authors have declared that no competing interests exist.

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