Effect of Decoration AgNO₃ - BaTiO₃ Nanoparticles on the Structure and Optical Properties of PVA/PEO Polymer Blend

The PVA and PEO polymers are important materials in industrial [1], medical [2], and electronics applications due to their distinctive properties, such as water solubility, thermal stability, and ease of molding [3, 4], PVA and PEO polymers have also been used as carrier for nano materials, enabling other applications such as coatings, paints, and water treatment systems [5-7]. However, these polymers suffer from deficiencies in crystalline structure [8] and optical properties [9], which limits their effectiveness in advanced applications. Therefore, improving the crystallinity, optical, and functional properties of these polymers represents an important research challenge.

Recently, metallic nanoparticles such as AgNO₃ and BaTiO₃ have gained increasing importance due to their nanoscale dimensions, large specific surface area, and surface energy sites, which give them unique capabilities to interact with polymeric matrices [10]. Bimetallic nanoparticles consist of two different metallic elements, and of increasing importance due to their unique structure, which can be in the form of random alloys, intermetallic compounds, or core-and-shell structures, these give them enhanced properties compared to monometallic nanoparticles [11]. Given their size range (1-100) nm, their physical and chemical properties on this scale open up broad prospects for scientific and technological applications [12].

In the current study, the addition of AgNO₃ and BaTiO₃ to the selected polymers increased the degree of crystallinity. The results of FTIR analysis showed the presence of interactions between the additives and the functional groups of the polymer, consistent with previous studies referenced in these studies [3, 13], confirming structural changes at the molecular level that improved the materials' optical and crystalline properties. Additionally, despite the several recent publications, this study utilized two types of nanomaterials to enhance polymer properties, resulting in a composite material suitable for various applications such as batteries, sensors, and smart membranes. The study employed an easy and environmentally friendly casting technique. The primary objective was to investigate the effect of nanoparticles on the structural and optical properties of polymer composites, specifically their impact on structural and optical characteristics.

The three nanocomposite membranes were prepared using a single technique. This technique was followed to first prepare the required weight ratios of the materials for each of the three samples, as shown in Table 2. The second stage was to dissolve the required weights of PVA and PEO in deionized water (H₂O) using a Stewart magnetic stirrer with a moving speed of approximately 40 revolutions in minute at room temperature 22℃ for 1.5 hours until a completely homogeneous solution was obtained. The polymer solution was then poured into a 5 cm diameter plastic Petri dish and left to dry for 10 days in an isolated place from dust and impurities. The first sample (Zo) used 0.80 g of PVA and 0.20 g of PEO, resulting in a transparent film.

The sample Z1 used the same weight ratio of PVA, 0.170 g of PEO, and 0.015 g of AgNO₃ and BaTiO₃. The final sample Z2 used the same weight ratio of PVA, 0.155 g of PEO, 0.015 g of AgNO₃, and 0.030 g of BaTiO₃. The thicknesses of the resulting films were measured by using micro printer, ranging from 94 μm to 100 μm. Where the particle size ranges between (56.85-94.58) nm for Zo, (22.39-50) nm for Z1, and (24.76-41.21) nm for Z2.

Table 2. The weight percentages for each sample

5.1 XRD analysis

Figure 1 presents the XRD patterns of pure PVA/PEO blend and the PVA, PEO, AgNO₃ and BaTiO₃ nanocomposite. The spectrum of pure PVA/PEO blend shows typical semicrystalline behavior, with three strong peaks at 2θ = 19.58°, 22.1° and 23.59°. The diffraction peaks observed correspond to the (040, 133 and 133) crystal structures of PVA/PEO polymers as indicated by standard reference patterns as shown in Figure 1(a). Additionally, smaller peaks appear at higher angles of 27°, 36°, and 39°, further supporting the concept that the polymers contain of both crystalline and non-crystalline regions. The broadening of these peaks in the polymers diffraction pattern suggests that the polymer exhibits a linear semicrystalline structure. This structural characteristic is crucial for stabilizing both chemically and electrochemically. The crystallization process in such polymers typically occurs through hierarchical organization across multiple length scales. During this process, the bending of polymer chains results in the formation of unique folded-chain layers that exhibit a specific molecular pattern. This chain-folding arrangement permits unconstrained expansion in two lateral dimensions. However, there is a limitation on the propagation of chain extension, with most defects concentrated at the folding surfaces. This finding is consistent with previous studies [14, 15].

Figure 1. XRD analyses of (a) PVA / PEO polymers blend for Zo, (b) PVA/PEO, AgNO₃ and BaTiO₃ nanocomposite for Z1 and (c) PVA/PEO, AgNO₃ and BaTiO₃ nanocomposite for Z2

In Figure 1(b), three strong peaks at 2θ = 19.61°, 22.4°, and 23.69° observed correspond to the (111, 102 and 020) crystal structures of PVA/PEO polymers. Additional peaks were also observed as a result of the addition of nanomaterials AgNO₃ and BaTiO₃. Peaks at 2θ = 31.92°, 39.25° and 47.74° correspond to the (113, 213 and 133) crystal structures of AgNO₃, the Bragg angle of AgNO₃ nanoparticles in the nanocomposites agrees with JCPDS data (Code 96-150-9469), peaks at 2θ = 31.92°, 50.94°, 56.48° and 65.71° correspond to the (113, 041, 240 and 151) crystal structures of BaTiO₃, the Bragg angle of BaTiO₃ nanoparticles agrees with JCPDS data (Code 96-152-5438).

Figure 1(c) shows peaks at 2θ = 19.4°, 23.46° and 23.51° observed correspond to the (011, 100 and 100) crystal structures of PVA/PEO. Peaks at 2θ = 31.65°, 39.03°, and 54.61° correspond to the (111 and 120) crystal structures of AgNO₃, and peaks at 2θ = 31.65°, 39.03°, 45.15°, 56.29°, and 65.96° correspond to the (111, 120, 022, 202, and 222) crystal structures of BaTiO₃ this behavior is similar to that presented by these studies [16, 17]. In summary, the XRD results show that adding more nanoparticles to the PVA/PEO matrix causes the peaks in the diffraction pattern to spread out more. This phenomenon can be attributed to structural modifications within the polymer matrix, which may stem from changes in the degree of crystallinity of polymers, shifts in polymer chain packing due to the incorporation of nanoparticles. From the X-ray diffraction (XRD) peaks, a number of structural parameters can be extracted to better understand the properties of the samples, where the interplanar d-spacing (d) is calculated using the Bragg Eq. (1) [18]:

$n \lambda=2 d \sin (\theta)$    (1)

where, n, λ, and θ mean the integer, wavelength, and angle of the X-ray between the incident and scattering beam, respectively. Meanwhile, the crystallite size (D) is calculated by applying the Scherrer Eq. (2) [19]:

$D=k \lambda / \beta cos (\theta)$    (2)

where, k = $\sim$0.9 is the factor of the crystals mean and β the full width at half the maximum peak (FWHM), as exposed in Table 3. The lattice strain (Ɛ) is measured by using Eq. (3) [19]:

$\varepsilon=\beta / 4 tan (\theta)$    (3)

The crystallite size (D) of samples was impacted and increased with adding the nanoparticles in polymer blend. The results show that the PVA/PEO polymer blend has a semi-crystalline nature with amorphous regions, while the introduction of nanomaterials AgNO₃ and BaTiO₃ contributed to the appearance of new peaks and increased the intensity of some crystalline peaks, indicating enhanced crystallinity and improved crystal structure of the sample. Table 3 contains important parameters for these films, intensity, distance between crystal planes, and full width at half maximum, crystallite size, and lattice strain.

Table 3. X-ray parameters for polymers and nanomaterials of prepared thin films

5.2 FTIR analysis

The main functions of using FTIR are to assess the type of chemical bonding between the different phases, and to examine whether there is a chemical reaction or just physical mixing, and to qualitatively analyze the materials present in the bulk of the films [20]. The FTIR analysis of PVA, PEO, AgNO₃ and BaTiO₃ films in the frequency region of 400 to 4000 cm^-1 was examined as illustrated in Figure 2. In Figure 2(a), blended polymers spectrum exhibited strong absorption peaks at 1096.62 cm^–¹ and 2884 cm^–1 corresponds to the C-O and C-H bending vibrations, respectively, of the polymers. Broad peak between 3500 to 3300 cm⁻¹ corresponds to the O–H bending vibrations and this behavior is similar to that presented by Abdali et al. [21]. In Figure 2(b), another new absorption peak located at 1340.73 cm^-¹ was associated with the N-O stretching vibration of AgNO₃. BaTiO₃ does not appear directly here because most of its vibrations appear in the very low infrared region, which may not be visible here. In Figure 2(c), other new absorption peak located at 606.30 cm^-¹ were associated with Ti-O stretching vibration of BaTiO₃ and this behavior is similar to that presented by Soliman et al. [22]. The peaks specific to PVA and PEO remain, indicating that the basic structure of the polymers is preserved. The increased appearance of new peaks and changes in intensity are evidence of an interaction between nanoparticles and polymer functional groups.

Figure 2. FTIR spectra of (a) PVA / PEO polymers blend for Zo, (b) PVA / PEO, AgNO₃ and BaTiO₃ nanocomposite for Z1 and (c) PVA / PEO, AgNO₃ and BaTiO₃ nanocomposite for Z2

5.3 Ultraviolet and visible analysis UV/Vis

The absorption spectrum was, measured using a dual-beam (UV-Visible - Spectrophotometer) this spectrometer, covers a wide area of the electromagnetic spectrum from the, ultraviolet region to the near-infrared region range of 190 to 1100 nm. UV-Vis spectroscopy measures the attenuation of a light beam after it passes through or is reflected from a sample. Figure 3 presents the absorption spectra of both pure PVA/PEO blend and the PVA, PEO, AgNO₃ and BaTiO₃ nanocomposite.

Figure 3. Absorbance spectra of (Z_O) PVA/PEO blend, and (Z1)(Z2) PVA, PEO, AgNO₃ and BaTiO₃ nanocomposite thin films

The pure polymers blend spectrum has a noticeable absorption peak between 190 to 250 nm and is due to electronic transitions n → π*, indicating absorption in the far-ultraviolet region. Upon incorporation of AgNO₃ and BaTiO₃ nanoparticles into the PVA/PEO matrix, a substantial rise in absorbance across the UV-Vis range is observed 300 to 450 nm. These absorptions for nanoparticles appear peaks at 420 nm. This is evidenced by an elevated absorption coefficient, suggesting a transition toward longer wavelengths. Silver nanoparticles exhibit distinct absorption due to the surface plasmon resonance (SPR) phenomenon in the range 400 to 450 nm. The concentration value has a high impact on the absorption spectrum which increases upon higher concentration value [23].

In general, samples containing nanoparticles show a clear increase in absorption between 300 to 600 nm. This is due to absorb the incident light by free electrons, then the absorption of samples Z1 and Z2, stabilizes at higher wavelengths compared to sample Zo. The absorption coefficient (α_o) is defined as a measure of the rate of decrease in the energy of the incident electromagnetic radiation per unit length along the direction of wave propagation within the material medium and is given by Eq. (5) [24]:

$\log (I / I o)=2.303 A=\alpha o d$    (4)

$\alpha \mathrm{o}=2.303 \frac{{A}}{{d}}$     (5)

where, I represents the intensity of the electromagnetic radiation (light) before entering the sample, Io the intensity of light after passing through the sample, d the thickness, and A is the absorbance.