Fabrication of (PVA-ZnO) nanocomposites and study of morphological, optical and electrical properties

doi:10.21203/rs.3.rs-4266378/v1

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Fabrication of (PVA-ZnO) nanocomposites and study of morphological, optical and electrical properties

https://doi.org/10.21203/rs.3.rs-4266378/v1

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This paper's goal is to prepare PVA with ratios of 0.2, 0.4 and 0.6 wt% by casting method and with a thickness of 270 ± 5 micrometers. The morphological characteristics were examined (FE-SEM and FTIR) and the results showed that the composites have a homogeneous and granular structure and that ZnO is well distributed within the polymer, The reason for the increased movement of charges is the action of a grid of nanomaterials inserted into the polymer. FTIR analyses the absorption peak seen at 3321.33 cm^− 1 is due to O-H bond that indicates the polymer and serves as its identity. The absorbance of the prepared composites showed an increase with increasing concentration of nanomaterials. In addition, the energy gap decreased with increasing concentration(2.8 to 2.5 eV) of nanomaterials, and all optical parameters (α, n, k_°, Ɛ_r, Ɛ_i) increased with increasing concentration of nanomaterials. For all samples, it is found that the dielectric constant decreases as frequency increases, it also increases with increasing concentration of nanomaterials within the polymer. The decrease in the effect of charge polarization is the main factor in the dielectric loss of the PVA-ZnO nanocomposite, the same time, increasing the concentration of nanomaterials leads to an increase in the value the dielectric loss. The increase in the frequency of the electric field and the increase in the concentration of nanomaterials increases the electrical conductivity. This makes these films useful for electronic applications and light filters, and they can also be used as ultraviolet detectors and humidity sensors.

nanocomposites

AC electrical

Morphological properties

Zinc oxide

Nanocomposites are materials whose dimensions are within the nano range. The reason for the appearance of a significant change in their final properties is as a result of the enormous interactions at the interfaces with respect to the size of the inclusion[1]. The nanocomposite does not differ from the traditional one in terms of the filling and matrix, but traditionally it uses, for example, glass or carbon fibers, while the nanocomposite uses a filling made of nanomaterial such as gold, silver, and silicon[2]. PVA is one of the most vital polymers that has the properties of non-toxicity, biocompatibility, and ability to dissolve in water. In addition, it has the ability to form hydrogels by physical and chemical methods[3]. Also, its optical and electrical properties, which depend on the type of doping, make PVA a material of interest to researchers, as well as its storage capacity[4]. The production of nanomaterial is what has enabled scientists to process atoms and molecules of size 1-100 nm. Small pieces can be used to make sensors and other devices based on these electrical and optical properties[2]. Zinc oxide has unique properties that have made it the focus of researchers' interest due to its applications in optical, electronic, sensing, and ultraviolet emitters[5]. The energy gap of zinc oxide is wide, which makes it one of the most promising semiconductor materials for optical applications in the ultraviolet spectral range[6]. The process of doping polymers and forming a matrix is beneficial for the formation of nanocomposites, and as a result, the structural and other physical properties will increase. Researchers have turned to manufacturing polymer-based nanocomposites for investment in electronic and optical applications, as well as in solar cells[3]. This work investigates the morphological, electrical and optical properties of the PVA-ZnO nanocomposite using FE-SEM spectroscopy, optical microscopy, and an FTIR spectrometer. The goal of this research is to create PVA-ZnO nanocomposites and analyse their electrical and optical properties, as well as some structural aspects, with the intention of employing them as humidity sensors.

Zinc oxide (ZnO): Zhengzhou Dongyao Nano Materials Co. LTD is a Chinese company from which this powder was obtained. Its features include a high purity of 99.99%, a white colour, a density of 5.606 g/cm3, and a nano particle size of 50 nm.

The molecular weight of the utilised polyvinyl alcohol (PVA) ranges from 26,200 to 30,400 g/mol. China's Shanghai Kaidu Industrial Development Co., Ltd. is the manufacturer of polyvinyl alcohol.

25 ml of distilled water was used to dissolve 1 g of PVA., and after the polymer was completely dissolved, a percentage of (0,2,4 and 6 )wt% znO was added. Then the nanomaterial was dispersed with an ultrasonic device. After that, the mixture was poured into dishes to a thickness of 270 ± 5 micrometers. After a week, measurements were taken for these films.

To use a material in optical applications and to make reflective coatings, one must have a detailed grasp of its optical constants throughout a wide range of wavelengths [7]. All materials' optical characteristics may be correlated with their electrical, electronic band, and atomic structures[8]. The Beer-Lambert equation is the equation by which the optical absorption coefficient can be described[9]:

𝛼 = $\frac{2.303\times A}{t}$ ……… (1)

The logarithmic relationship between the incident intensity I_o and the reflected I_A is known as absorbance A [10]:

A= - log ${\text{T}}_{r}$ = log (I_o / I_A) ……………………. (2)

Optical constants, such as complex dielectric (εr and εi), extinction coefficient (k), and index of refraction (n), are the constants through which the optical properties of films can be described[11]:

$$\text{k}=\frac{{\alpha } {\lambda }}{4 {\pi }}$$

………

𝑛 = ( $\frac{1 + R1/2 0 }{1 - R1/2 0}$) ……. (4)

Through the two equations, complex dielectric constants can be calculated[12]:

ɛ_r=n²-k² ………… (5)

ɛ_i=2nk ………….. (6)

As for the optical energy gap, it can be determined from that region as shown in the following relationship[13]:

αhυ = β(hυ-Eg)^r ……..(7)

The presence of free ions in the polymer is what helps increase its electrical conductivity.

σ_v = $\frac{1}{{{\rho }}_{\text{v}}}$ = $\frac{L}{{R}_{V}{A}_{r}}$ …..(8)

Using the Debye equation, the dielectric constant can be calculated

ɛ = ɛ^/ - i ɛ^// ……(9)

ɛ^// represent dielectric loss[14] .

Morphological properties

The purpose of the FE-SEM examination is to clarify the density and distribution of the nanoparticles in the manufactured polymeric film, as the images showed a homogeneous distribution of ZnO within the polymer. The image also showed that the ZnO nanoparticles appear to have been coated with the polymeric material (PVA)look in Fig. (1)[3]. Increasing the number of ZnO molecules represented in a network in the polymer matrix increases the conductivity due to its ability to accelerate electron motion, and this is the main reason that justifies the reduction in the E_g[15]. Other nanomaterials, such as graphene, can be used[16]. Figure 2 illustrates the FTIR study of (PVA/ZnO) nanocomposites, the O-H bond is responsible for the absorption peak observed at 3321.33 cm^− 1 that indicates the polymer and serves as its identity. It traps water from the air, which is typical in humidity sensor applications[3]. The vibration peaks that appeared at 1567.03and1010cm^− 1 indicate the weak Zn-o and Zno₂ bonds. When adding )ZnO) nanomaterials to the polymer and varying the concentration, some changes were observed in the vibration peaks, and no creep of the peaks was observed. This means that the reaction occurring is physical[2–3].

Optical properties

Figure 3 showed the absorption for samples with a thickness of 270 ± 5 micrometers. The absorption in the ultraviolet region is high and began to decrease from a wavelength of 400 nm. Additionally, with increasing concentration of the (ZnO) nanomaterial, the absorption decrease even with increasing wavelength[17]. The absorption coefficient can be calculated from Eq. 1. Show Fig. 4: With increasing energy, the absorption coefficient increases, through which the type of electronic transitions can be determined. This increase is due to an increase in the concentration of zno, which leads to electronic crossing between the partial orbitals, with the help of phonons, and the electronic momentum is preserved[3, 18]. It is possible to draw a tangent slope for all films, which shows the energy gap versus the photon energy. The results also showed that by increasing the concentration of nanomaterials (ZnO), the energy gap decreases, which explains the narrowing of the crossing region from the valence band to the conduction band and the increase in the movement of electrons[19]. Figure 5 showed that the energy gap decreased (2.8–2.5) eV, the reason for this decrease is the creation of local levels as a result of the increase in nanomaterials ZnO in the polymer. This nanocomposites shows that it can be used as a humidity sensor. These nanocomposites are also used in optical applications[19.20]. The increase in the concentration of nanomaterials (ZnO) increased the extinction coefficient, as shown in Fig. 6 [21]. Because of the link between them, the extinction coefficient curve behavior of nanocomposites is comparable to the absorption coefficient (see Eq. 3) [9]. Furthermore, the sharp increase in the extinction coefficient occurred at the absorption edge. These results could be ascribed to both increase absorbance because of the transmission phase, and increase scattering due to increase, this matches the FE-SEM images in morphological characteristics[22–23]. Figure 7 shows that when the concentration of nanomaterials (ZnO) increases, so does the refractive index. The optical energy gap and reflectivity of the films are to blame. The packing density and greater orientation are related to variations in (n) value[24]. The amount by which a substance slows the speed of light is proportional to its real component. The imaginary fraction, Ɛ_i, shows how a dielectric absorbs energy from an electric field through dipole motion. As a result of kₒ² being less than n² look in Eq. 5, the behavior of ̐ Ɛ_r in Fig. 8 is comparable to the refractive index performance. In Fig. 9, however, Ɛ_i mostly depends on the value of the extinction coefficient (kₒ) look in Eq. 6 [25].

AC Electrical

Using Eq. (9), the dielectric constant (ε') of (PVA-ZnO) nanocomposites was determined. Figures (10) illustrates the behavior of the (PVA-ZnO) nanocomposites' dielectric constant with frequency. The dielectric constant is found to decrease with increasing frequency in all samples. This phenomenon can be attributed to the dipoles in nanocomposites turning in the direction of the applied electric field and the reduction of space charges or interfacial polarization to overall polarization. [26]. Figures (11) illustrates how the dielectric constant of (PVA-ZnO) nanocomposites varies with the amount of nanoparticles present at f = 100 Hz. This indicates that the dielectric constant of (PVA-ZnO) nanocomposites rises as the amount of (ZnO) nanoparticles grows. It is noted that for all samples of nanocomposites, increases with increasing nanoparticle loading. Interfacial polarisation within the nanocomposites in the applied field alternating electric field and an increase in charge carriers could be used to characterise these processes. [27]. This indicates that produced nanocomposites have low loss, or low energy loss, making them appropriate for use in pressure sensor and nanoelectronics applications.

The dielectric loss (${\epsilon }^{{\prime }{\prime }}$) was calculated from equation (‎9). Figure ‎(12) demonstration the behavior of dielectric loss for (PVA-ZnO) nanocomposites with frequency. It has been observed that as frequency increases, the dielectric loss of (PVA-ZnO) nanocomposites decreases, which is caused by a decrease in the influence of space charge polarisation. The dielectric loss is highest at low frequencies and decreases as frequency increases. This is because the electric dipoles have adequate time to align with the electric field before changing direction [28]. The effect of (ZnO) concentration on the dielectric loss of (PVA) polymeric at f = 100 Hz is seen in Fig. 13. An increase in the amount of nanoparticles causes a rise in the dielectric loss values, which is explained by an increase in the quantity of charge carriers [29]. Clusters are formed when the amount of nanoparticles in the nanocomposites is minimal, but when the concentration is high-up to 6%wt they combine to form networks. The dielectric loss of nanocomposites rises as the amount of (ZnO) NPs in them grows, as the figures illustrate. As the amount of ZnO NPs in the polymeric (PVA) grows, so does its dielectric loss value, which is explained by the increase in charge carriers for the nanocomposites [30].

To measure the A.C electrical conductivity of nanocomposites, use equation (‎8). Nanoparticles produce a route network inside the nanocomposite at high concentrations of nanoparticles (6wt.%) for (PVA) polymer. Figures (14) displays the fluctuation in electrical conductivity of PVA-ZnO nanocomposites with frequency. As demonstrated in the Figures, for all prepared nanocomposites, the electrical conductivity rises as the electric field frequency increases. This behaviour is caused by both the hopping process, which moves charge carriers, and space charge polarisation, which happens at low frequencies. For (PVA-ZnO) nanocomposites, the electrical conductivity rises with increasing frequency due to the enhanced mobility of charge carriers in the high-frequency region[31].In Fig. 15 shows how (ZnO) nanoparticles affect the electrical conductivity of (PVA) polymer at 100 Hz. According to the figures, by increasing the concentration of (ZnO) nanoparticles. Because of the composition of the dopant nanoparticles, which gradually reduce the resistance of nanocomposites and increase the electrical conductivity, the growth in electrical conductivity with growing content of (ZnO) nanoparticles is attributed to an increase in the number of charge carriers. This aligns with the findings of the study [32–33].

The results showed that the prepared films are homogeneous and the diffusion of the nanomaterial within the polymer is good, which in turn enables the electrons to move more freely. FTIR analyses the absorption highest seen at 3321.33 cm^− 1 is due to O-H bond that indicates the polymer and serves as its identity. It traps water from the air, which is typical in humidity sensor applications. Additionally, excellent absorption in the UV region, that as the amount of nanomaterials increases, their energy gap shrinks to between 2.8 and 2.5 eV, and that all optical constants increase with increasing concentration of nanomaterials. Therefore, they can be used as detectors in the UV region. As the frequency and concentration of nanomaterials increase, the dielectric constant, dielectric loss and AC electrical conductivity increase

Author Contribution

The work is shared between the researchers in all steps, from the beginning, when samples were prepared, to the interpretation of the results

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No competing interests reported.

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Fabrication of (PVA-ZnO) nanocomposites and study of morphological, optical and electrical properties

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1. Introduction

2. Preparing materials

3. Theoretical part

4. Results and discussion

Conclusion

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Author Contribution

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