PC blend

Physica B: Condensed Matter 560 (2019) 185–190

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Role of ZnO nanoparticles on the structural, optical and dielectric properties of PVP/PC blend

T

Naziha Suliman Alghunaim, H.M. Alhusaiki-Alghamdi∗ Department of Physics, Faculty of Science, University of Jeddah, Jeddah, Saudi Arabia

A R T I C LE I N FO

A B S T R A C T

Keywords: PVP/PC blend ZnO nanopowder X-ray FT-IR Dielectric properties

Polymer nanocomposite films based on poly (vinyl pyrrolidone) (PVP) and polycarbonate (PC) blend (60/40 wt %) doped different concentrations (≤0.6 wt%.) of zinc oxide (ZnO) nanopowder are prepared and characterized using various techniques. The change of the structure of the films are characterized using X-ray diffraction, Fourier transform infrared (FTIR) and UV–Vis spectroscopy. The semicrystalline nature of the structure of these nanocomposites have been observed from X-ray spectra and its effect after addition of ZnO. The main characteristic of IR bands of PVP and PC are observed. The intensity of some bands has significantly reduced with the stretch of the broad band at 2887 cm−1 confirms that the ZnO interacts with the functional groups in PVP/PC blend. The ultraviolet–visible (UV–vis) spectra is studied. The values of the optical energy band gap (Eg) are decreased attributed to the changes of the structure in the nanocomposites that occur after the addition of ZnO. The values of ε ' and ε '' gradually decrease with increase of the frequency and they reached to constant values at higher frequencies attributed to the polarization. The variation of modulus parameters M′ and M′ ′ against Log (f) are studied. The lower values of the modulus parameters M′ and M′ ′ are the indication of transport of the ions and it is the approach towards the relaxation at high frequency. The plot of Z″ as a function of Z′ shows a semicircle which indicates the presence of heterogeneous or broad relaxation processes. The decrease of tan δ since hopping frequency of charge carriers don't follow the change of applied field.

1. Introduction

to form a blend with different polymers. Hydrogen-bonding may occur between the polymer blend. To obtain a novel polymer nanocomposite material, the blends between different polymers wind up a helpful, viable, basic, easy and green method to a synthesis of advanced polymeric materials with well physical properties required for industrial applications [10]. Nanoparticles have attracted wide consideration because of their one of a kind properties and interminable promise in material science. Nanoparticles have an extensive surface region, which expands their reactivity. Therefore, the incorporation of nanoparticles into organic polymer matrices is expected to have enormous technological applications [11]. The inorganic nanomaterial shows wide industrial use of the second-age microelectronic devices, solar cells, gas sensors, memory devices and the nanodielectric applications [12–14]. So, the inorganic materials as a good filler are utilized for the blend of the polymer nanocomposites [15]. The spectroscopies measurements, thermal analysis, mechanical properties, the dielectric and electrical investigation proved that these new materials comprise most of the useful properties of nanocomposite materials [16].

Nanocomposites materials made between polymer and additionally polymer blend doped nanoparticles [1,2]. The poor thermal, mechanical, and electrical properties of the polymer constituent are repaid utilizing nanoparticle material as a filler having great optical, electrical, and mechanical properties [3]. Polycarbonate (PC) is a thermoplastic polymer containing carbonate units in their synthetic structure [4,5]. The PC is commonly used in different commercial applications. The modern applications are for the most part constrained to low sub-atomic weight polycarbonate for polyurethane creation [6]. The PC got their name since they are polymers containing carbonate groups (−O−(C]O)eO−). Also, PC is used for electronic applications and it tends to be utilized in different items related to electrical and media communications. PC can be used it as a dielectric in high-stability capacitors [7]. Poly (vinyl pyrrolidone) (PVP) is a vinyl polymer having planar and significantly polar side groups in the ring [8]. The PVP is an amorphous polymer and has high Tg considering the proximity of the firm pyrrolidone group [9], which is strong a depicts the polar group and is known

∗

Corresponding author. E-mail address: [email protected] (H.M. Alhusaiki-Alghamdi).

https://doi.org/10.1016/j.physb.2019.02.021 Received 30 January 2019; Received in revised form 11 February 2019; Accepted 13 February 2019 Available online 14 February 2019 0921-4526/ © 2019 Elsevier B.V. All rights reserved.

Physica B: Condensed Matter 560 (2019) 185–190

N.S. Alghunaim and H.M. Alhusaiki-Alghamdi

Zinc oxide (ZnO) nanoparticles are noticed as reinforcement materials to fabricate polymer nanocomposite materials due to their compatibility, high ultraviolet absorption, good optical transparency, great electron mobility, and stability. The ZnO has attracted consideration as a novel strong performance and fine metal semi conductive in various applications as optics, electronics and optoelectronics applications [17]. The ZnO nanoparticles got using various systems. ZnO nanoparticles are used as a nanofiller to reinforce for polyethylene, polypropylene, polystyrene, etc. Generally, the modification of any physical properties depends on the kind of the polymer and on the nanosize, distribution and dispersion of the nanofillers. Then, ZnO nanoparticles are one of the most industrial materials have various superior electronic and optoelectronic properties. A few reports have studied the improvement of ZnO-polymer composites for various applications [18–21]. Overview of the literature depicts that the structural, thermal and electrical properties of the PVP/PC blend incorporated ZnO nanopowder is not investigated in detail. As detailed over, the PVP/PC blend is used as a basic polymeric matrix to the preparation of different nanocomposites attributed to its improved properties over the pure polymers. Then, in the present article, the spectroscopic and electrical studies of the PVP/PC blend doped different concentration (0.0, 0.15, 0.30, 0.45 and 0.60 wt) of ZnO nanocomposites. The prepared nanocomposites have been carried out and the results are analysed in regard to their technological applications as advanced functional materials.

O

N

Zn

H CH3 O CH3

O

N

O OC

n

CH3

O H H

H

Zn

Zn

CH3

O OC

H H

n

O

N

PVP

PC

PC/PVP-ZnO Scheme 1. The possible interaction mechanism of PVP/PC-ZnO nanocomposites.

Intenisity (a. u.)

0.60

2. Experimental work

0.45

0.30

2.1. Material

0.15

Polyvinyl pyrrolidone (PVP) has average molecular weight 1.0 × 104 with linear formula (C6H9NO)n and commercial polycarbonate (PC) has Mw = 2.47 × 104 with linear formula (C15H16O2)n are a supplied by Sigma-Aldrich. The Zinc oxide (ZnO) nanopowder with size < 100 nm is used as a filled and the chloroform is used as a solvent to polymer blend and the filler.

PVP/PC 10

20

30

40

50

60

70

2 (degree) Fig. 1. The X-ray diffraction of PVP/PC pure blend filled ZnO nanopowder.

2θ = 17.88° confirms the semi crystalline nature of pure PVP/PC blend. It is due to the PVP used in the blend is amorphous. The X-ray peak at 2θ = 18.15° is observed for pure PVP [22,23]. In the PVP/PC-ZnO nanocomposites, the intensity of the broad peak is decreased with the increase of their width increased with an increase of ZnO nanopowder indicates that an increase in the amorphous region, which might cause an increase of the electrical conductivity. This demonstrates that complexation between ZnO and PVP/PC blend occur in the amorphous region inside the polymeric matrices. Some peaks are observed due to ZnO nanopowder indicating a hexagonal wurtzite structure of ZnO. The values of lattice planes (hkl) of the peaks at 2θ = 31.06°, 34.1° and 41.56.41°, 62.87°, 67.90° and 68.94° are assigned to the (100), (002), and (110) planes of ZnO, respectively [24]. The wurtzite structure of ZnO is attributed to JCPDS (card number: 00-005-0664) [25].

2.2. Samples preparation The quantity of PVP and PC (60/40 wt/wt %) was dissolved in chloroform separately with stirring. ZnO nanopowder was also dissolved in chloroform. The materials were used for the preparation of (PVP/PC)-ZnO films by the solution-cast method. The resulting solution of ZnO was added drop by drop to the polymer solution with mass fraction of 0.15, 0.30, 0.45 and 0.60 %wt. The resulting solution was cast onto glass Petri dishes and kept in a dry atmosphere at room temperature about 2 days prior to their measurements. The films thickness is in the range of 100 μm. 2.3. Used techniques The X-ray diffraction is measured on a PANalytical X'Pert PROXRD analyzer with CuKα radiation (λ = 1.54056 Å) using 30 kV. The FT-IR is measurement on Nicolet iS10, USA spectrometer with resolution 4 cm−1 and the wave number range 4000 to 400 cm−1. Ultraviolet–visible (UV–vis) spectra are measured by (V-570 UV/VIS/ NIR, JASCO) with wavelength range 190–900 nm. The AC electrical measurements are measured in a frequency range 10−1-107 Hz. The possible interaction mechanism of PVP/PC-ZnO nanocomposites is drown in Scheme 1.

2.5. FT-IR study The Fourier transform infrared (FT-IR) spectra of pure PVP/PC blend and the blend doped different concentrations of ZnO nanopowder measured at room temperature are recorded in Fig. 2. It is observed that the IR spectrum of pure PVP/PC blend film exhibits all the main characteristic bands of the PVP and the PC. The bands of pure PVP is assigned as: The bands at 1454 cm−1 and 1288 cm−1 are attributed to CH2 wagging and asymmetric twisting vibration mode. The sharp bands appearing at 1087 cm−1 and 834 cm−1 are due to the CeO and CeC stretching vibrational modes. The small band appears at 1494 cm−1 is assigned to the characteristic stretching vibration of the C]N (pyridine ring) in the PVP structure [26,27]. The assignments of IR bands of PC are clear that: The broad band

2.4. X-ray diffraction The X-ray diffraction of PVP/PC incorporated by Zinc oxide (ZnO) nanopowder at 2θ = 5°–70° at room temperature are depicted in Fig. 1. The X-ray spectra shows abroad from 2θ = 12.93°–21.57° centered at 186

Physica B: Condensed Matter 560 (2019) 185–190

N.S. Alghunaim and H.M. Alhusaiki-Alghamdi

samples. The optical band gap of the PVP/PC-ZnO nanocomposites can be calculated through the linear portion of visible UV–Vis spectra, the optical energy band gap (Eg) of these nanocomposites can be analysed by the following equation [30,31]:

Absorbance (a. u.)

0.60 ZnO

(αhυ) m = B(hυ−Eg)

0.45 ZnO

where, α is the absorption coefficient, hν is the photon energy, B is a constant, and m is a variable having values 1/2, 2, 3/2 and 3 due to the allowed indirect, allowed direct, forbidden direct and forbidden indirect transitions, respectively [32]. Measurement of absorption spectra is one of the most common and direct methods to study the ribbon structure of polymer films. In this method, the absorption coefficient α(ν) is calculated using the following expression:

0.30 ZnO 0.15 ZnO

PVP/Pc

α(ν) = 4000

3500

(1)

3000

2500

2000

1500

1000

500

2.303 A t

(2)

where A is absorbance and t are the thickness of the sample. At near band edge, the allowed direct occur in the photon energy (hν) and the band energy due to these transitions can be evaluated by plotting (αhν)1/2 against photon energy (hν). Fig. 4 shows the relation between (αhν)1/2 and the photon energy (hν) for the PVP/PC-ZnO nanocomposites. The curves showed that no complete linear relationship was observed but the best line is determined using extrapolating of the linear portion to the most appropriate line on the photon energy axis of the forbidden direct optical energy band gap (Eg) of the samples. The values of Eg are decreased with increased ZnO content from 3.73 eV to 3.17 eV. This behaviour is related to the changes of the inside the nanocomposites that occur after the addition of ZnO. This change, which indicates a decrease in the energy-band gap, increases the electrical conductivity of the prepared samples. The decrease of Eg values may be return to the formation of defects (disorder) and/or to the lower band gap of ZnO. This behaviour will effect of the optical properties of the prepared samples.

-1

Wavenumber (cm ) Fig. 2. The FT-IR spectra of PVP/PC pure blend filled ZnO nanopowder.

centered at 2887 cm−1 is due to eCH stretching aromatic ring. The sharp bands observed at 1774 cm−1, 1501 cm−1 and 1197 cm−1 are attributed to stretching carboxyl group (C]O), C]C-vibration mode and to asymmetric stretching carbonate group (OeCeO), respectively [28,29]. After adding of ZnO nanopowder to the PVP/PC blend, the intensity of the band at 2887 cm−1 and 1774 cm−1 (C]O and CH) have significantly reduced which confirms that the ZnO interacts with these functional groups. Further, the broad band at 2887 cm−1 (eCH) is stretched. Further, there is an increase in other absorption intensity of the bands with increasing of ZnO content. In addition, the broadness of vibrational bands ν(OH), ν(CH) and ν(CeOeC) increase with increasing ZnO content in blend sample. However, the absorption bands appeared at ∼600 and ∼558 cm−1 are reflected in the presence of nano-ZnO vibrational groups. These results indicate that certain interaction occurred at the interface of ZnO nanoparticles.

2.7. The AC electrical studies 2.7.1. The dielectric properties The variation between the dielectric constant (ε ') and the dielectric loss (ε′ ′) with the frequency Log (f) of pure PVP/PC blend and the blend doped 0.0, 0.15, 0.30, 0.45 and 0.60 wt% of Zinc oxide (ZnO) nanopowder, at room temperature, are recorded in Fig. 5 (a and b). It is seen that, the curves of both ε′ and ε″ are dramatically decreased with the increase of frequency. This behaviour is a general trend of dielectrics materials as a polymer attributed to the polarization which created

2.6. UV–vis spectra The UV–Vis spectra of the PVP/PC blend and the blend doped ZnO in the 190–800 nm wavelength range are recorded in Fig. 3. The absorption edges in the spectra are clear at 303 nm attributed to the semi crystalline behaviour of these nanocomposites in the spectra for all the

12

2.0x10

0.60 12

Absorbance (u. a.)

1.5x10

0.45

( h ) (eVcm )

-1 3/2

0.60 ZnO 0.45 ZnO

1.0x10

0.30

3/2

0.30 ZnO

12

0.15 ZnO

0.15 11

5.0x10

PVP/PC 0.0

PVP/PC 200

400

600

800

1000

3.73

3.17 1

2

3

4

5

6

7

h (eV)

Wavelength (nm)

Fig. 4. The variation of (αhυ)1/2 depends on the energy (hυ) of PVP/PC pure blend filled ZnO nanopowder.

Fig. 3. The UV–Vis spectra of PVP/PC pure blend filled ZnO nanopowder. 187

Physica B: Condensed Matter 560 (2019) 185–190

N.S. Alghunaim and H.M. Alhusaiki-Alghamdi 100

75

'

ε′ = ε∞ +

PC/PVP 0.1 ZnO 0.3 ZnO 0.6 ZnO 0.9 ZnO

(a)

'

25

0 2

4

6

Log (f/Hz)

300

PVP/PC 0.15 ZnO 0.30 ZnO 0.45 ZnO 0.60 ZnO

(b) 250

''

200

(4)

''

The behaviour of both ε and ε in the figure can be discussed as the following. The values of ε ' and ε '' are gradually decrease with the increase of the frequency and they reached to constant values at higher frequencies attributed to the polarization effects and to the dipoles, not start to follow the field variety at higher frequencies. The curves of ε′ and ε″ as shown in the figures exhibit three regions. In the first region at very low frequencies (ω ≪ τ ⇒ ε′ = εs ). Then, the dipoles flow the field and the values of ε′ and ε″ decrease attributed to the dominant contribution of interfacial polarization effect. The second 1 region (ω ≤ τ ), the dipoles begin to lag the field and the relaxation process occur. At the last region (ω ≫ τ ), the linearity of ε′ is tending to approach steady state which can be assigned to the high frequency limiting permittivity ε∞ values of the polymers. When ωτ ≪ 1, the estimated values ε′ of is equal to εs. Whereas the plot of ε″ decreases a little until it becomes very slow. For PVP/PC-ZnO nanocomposite films, when the frequency is increased, then the dipole will no longer be able to rotate rapidly sufficiently and the oscillation being the lag those of the applied field. As frequency increases, the dipole will be completely unable to follow the field and the orientation stopped and the value of ε′ is decreased and approach stability due to interfacial polarization.

50

0

εs − ε∞ (ε − ε∞) ωτ and ε′ ′ = s 1 + ω2τ 2 1 + ω2τ 2

2.7.2. Modulus study The modulus behaviour is used to provide a better insight into the dielectric behaviour of the polymeric nanocomposite materials. The modulus study is used to investigate the conductivity relaxation by suppressing the effect of polarization at low frequency. Then, the dielectric results are transformed into the modulus results. The correlation between the complex permittivity (ε ∗) and modulus parameters (M' and M'' ) can be written as [36]:

150

100

M ∗ = M′ + M′ ′

50

(5) ′

M′ =

0 0

2

4

6

(6)

′

The variation of M′ and M′ against Log (f) is shown in Fig. 6 (a and b). The lower values of the modulus parameters M′ and M′ ′ are the indication of transport of the ions and it is the approach towards the relaxation at high frequency. At high frequency, the values of both M′ and M′ ′ reaches to zero and large capacitance is seen attributed to polarization effect.

Log (f/Hz) Fig. 5. The variation of: (a) the dielectric constant (ε ' ) and (b) the dielectric loss (ε '' ) depends on frequency (Log f) of PVP/PC pure blend filled ZnO nanopowder.

related to the ionic exchange of the number of ions by locally displacing in the applied field direction. Where, the dielectric constant (ε ' ) of the polymer occurred due to the dipolar, electronic, ionic, and interfacial polarizations. When the frequency (f) is low, there is a charge accumulation at the interface causing contributions for various interfacial polarizations are observed. This behaviour is because the space charges can't support and comply with the outside field which causes a decrease in the polarization and there is no charge accumulation at the interface. Also, dielectric constant (ε′) and dielectric loss (ε′ ′) depend on to the presence of ion centre type of polarization in the films and to the interfacial polarization. The complex permittivity (ε ∗) related to free dipole oscillating can be studied according to Debye relation as [33,34]:

ε − ε∞ ε ∗ = ε′ − iε′ = ε∞ + s 1 − jωτ

ε′ ε′ and M′ ′ = 2 ε′ + ε′ ′ 2 ε′ 2 + ε′ ′ 2

2.7.3. Complex impedance study The complex impedance (Z*) study can be applied to identify whether the long-range or short-range movement of charge carriers is dominant in the relaxation process. To interpret the dielectric spectra, different formalism such as complex impedance Z* has been explored. The complex impedance (Z*) can be calculated as [37]:

Z ∗ = Z′ + iZ′ ′

(7)

where Z′ and Z″ are the real and imaginary part of the complex impedance, which described as [38]:

Z′ =

R ωτ and Z′ ′ = 1 + ω2τ 2 1 + ω2τ 2

(8) ′

The plot between the real part (Z′) and the imaginary part (Z′ ) with Log (f) is shown in Fig. 7 (a and b). The values of both Z′ and Z″ are gradually decreased with the increase of frequency. This behaviour is a general trend of the polymeric materials can be understood by polarization which created related to the ionic exchange of the number of ions by locally displacing in the applied field direction. At lowest frequency, there is a charge accumulation at the interface causing contributions for various interfacial polarizations are watched. The discussion of this behaviour is that at a certain point, the space charges

′

(3)

where ε∞ is the dielectric constant at high frequency and εs is the dielectric constant at the lower frequency and the relaxation time (τ = RC). The dielectric constant (real part ε ' ) and the dielectric constant (imaginary part ε '' ) are written in the form [35]:

188

Physica B: Condensed Matter 560 (2019) 185–190

N.S. Alghunaim and H.M. Alhusaiki-Alghamdi

PVP/PC 0.15 ZnO 0.30 ZnO 0.45 ZnO 0.60 ZnO

4

8.0x10

(a)

4

6.0x10

PVP/PC 0.15 ZnO 0.30 ZnO 0.45 ZnO 0.60 ZnO

10

5x10

(a) 10

4x10

10

Z'

M'

3x10 4

4.0x10

10

2x10 4

2.0x10

10

1x10 0.0

0 0

2

4

6

0

Log (2)

4

4

(b) 9

9.0x10

Z''

M''

PVP/PC 0.15 ZnO 0.30 ZnO 0.45 ZnO 0.60 ZnO

10

4

4.0x10

9

6.0x10

9

3.0x10

4

2.0x10

0.0

0.0 0

2

4

0

6

2

4

6

Log (f/Hz)

Log (f)

Fig. 7. The variation of: (a) the real part of impedance (z ′) and (b) of the imaginary part of impedance (z ′′) depends on frequency (Log f) of PVP/PC pure blend filled ZnO nanopowder.

Fig. 6. The variation of: (a) the real modulus (M' ) and (b) the imaginary modulus (M'' ) depends on frequency (Log f) of PVP/PC pure blend filled ZnO nanopowder.

can't support and comply with the outside field which causes a decrease in the polarization and there is no charge accumulation at the interface. The complex impedance is high at the low frequency that might be because of space charge polarization. It is because obstructing of charge carriers at the electrodes due to confinement to their movement at the interface. The plots further show a decrease in impedance with the increase in ZnO content. Fig. 8 shows the plot of Z″ as a function of Z′ for the prepared samples. All curves display a semicircle indicates heterogeneous founded or broad relaxation processes. Furthermore, if one single semicircle is observed, this mean that a single relaxation in this system is occurs. No complete semicircle is seen, extrapolation may be done for good visibility. The smallest semicircles diameters of this system are associated with the highest capacitance. Fig. 9 displays the plot between the loss tangent (tan δ) with the frequency of the prepared films at room temperature. The estimated values of tan (δ) are obtained from the relation [39,40]:

10

1.2x10

9

Z''

9.0x10

9

6.0x10

PVP/PC 0.15 ZnO 0.30 ZnO 0.45 ZnO 0.60 ZnO

9

3.0x10

0.0 0

10

1x10

10

2x10

10

3x10

10

4x10

10

5x10

Z' Fig. 8. The plot of Z″ as a function of Z′ of PVP/PC pure blend filled ZnO nanopowder.

ε '' ε'

6

1.2x10

PVP/PC 0.15 ZnO 0.30 ZnO 0.45 ZnO 0.60 ZnO

6.0x10

tan δ =

4

Log (f/Hz)

(b)

8.0x10

2

(9) 189

Physica B: Condensed Matter 560 (2019) 185–190

N.S. Alghunaim and H.M. Alhusaiki-Alghamdi

5

form between Z″ with Z′ plot is indicating the presence of heterogeneous or broad relaxation processes. The smallest semicircles diameters of this system are associated with the highest capacitance. The decrease of loss tangent (tan δ) behaviour attributed to the fact that the hopping frequency of charge carriers don't follow the change of the applied field.

PVP/PC 0.15 ZnO 0.30 ZnO 0.45 ZnO 0.60 ZnO

4

3

tan

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1

0 0

2

4

6

Log (f, Hz) Fig. 9. The plot between the loss tangent (tan δ) with the frequency of pure blend filled ZnO nanopowder at room temperature.

From the plot, it is observed that the values of loss tangent (tan δ) for all films decreases with increasing of the frequency. The decrease is due to the fact that hopping frequency of charge carriers don't follow any changes of applied field. Also, the increase of tan d with the increase of ZnO content is expected due to the increase of the conductivity as the increase of ZnO. 3. Conclusion The PVP/PC-ZnO polymer nanocomposites are prepared by solution casting method and characterized by X-ray diffraction, FT-IR) and UV–Vis spectroscopy. The dielectric and modules parameters, complex impedance and tan δ are measured. The X-ray revealed that the semicrystalline structures of this nanocomposite is observed after addition of ZnO. From FT-IR study, the intensity of some the bands is reduced confirms that the ZnO interacts with the functional groups in the blend. The absorption bands appeared at ∼600 and ∼558 cm−1 are reflected in the presence of nano-ZnO vibrational groups. The value of the energy band gap (Eg) from UV–Vis spectra is decreased due to the changes of the structure (disorder structure) in the nanocomposites that occur. The behaviour of both ε ' and ε '' is discussed as the following: the values of ε ' and ε '' are gradually decrease with the increase of the frequency and they reached to constant values at higher frequencies attributed to the polarization effects. The lower values of the modulus parameters M' and M'' are the indication of transport of the ions. At high frequency, the values of both M' and M'' reaches to zero and large capacitance is seen attributed to polarization effect. The values of both Z′ and Z″ are gradually decreased with the increase of frequency attributed to polarization which created related to the ionic exchange of the number of ions by locally displacing in the applied field direction. The semicircle

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