Effects of SiO 2 Nanoparticles on Polyvinyl Alcohol/Carboxymethyl Cellulose Polymer Blend Films ’ Structural, Wettability, Surface Roughness, and Optical Characteristics

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Introduction
Blended polymers are a hot topic in the scientific community due to their remarkable physicochemical properties [1,2].The optical properties of blended polymers make them a compelling and promising area of research.Researchers have been eagerly exploring their possible uses in various fields, like electronics, energy, and medicine [3].These mixed films have consistently proven to be superior in terms of performance, durability, and versatility.Mixed films are the clear choice for developing cutting-edge electronics or simply seeking to improve existing technology [1,[4][5][6][7].Blended polymers have the unique ability to modify their structure and composition to customize their optical behavior, which makes them very promising for creating innovative technologies.
Polyvinyl alcohol and sodium carboxymethylcellulose (PVA and CMC) are compatible polymers that form highly transparent blend films.PVA and CMC share characteristics like water solubility, nontoxic, abundant, cross-linked, and biodegradable polymers [8].CMC is a pH-sensitive ionic polyelectrolyte with carboxyl groups [9].The combination of CMC and PVA presents an opportunity to achieve the benefits of both materials.In addition, the presence of the hydroxyl (OH) groups in the backbone of PVA and CMC may lead to the formation of inter-and intra-hydrogen bonds [5,10].
Metal oxide-polymer composites have recently gained significant research interest for their applications in catalysis, electronics, photonics, and optoelectronics [11].Additives of nanosized inorganic particles in the polymeric matrix create nanocomposites with unique properties distinct from conventional materials [11][12][13][14][15][16][17].Recently, ferrite nanoparticles were used as additives in a PVA/CMC blend matrix to tune the optical parameters to be used in various optical applications [18,19].SnS [20][21][22], Co 0.9 Cu 0.1 S [23], and Ag/CuS [24] nanoparticles were added to the PVA/polyvinyl propylene (PVP) blend film to adjust its optical parameters and make it suitable for optoelectronic applications.PVA/PVP blend films reinforced with SiO 2 have previously been discussed in terms of their structural and optical properties [25,26].The use of SiO 2 as a nanofiller for PVA/CMC blend films was rarely discussed.The influence of SnO 2 /SiO 2 and Cr 2 O 3 / SiO 2 nanocomposites on the optical parameters and structural features of the PVA/CMC matrix have been discussed [27,28].The integration of SiO 2 nanoparticles has played a pivotal role in revolutionizing the enhancement of polymer surfaces' morphological structure and optical characteristics.Previously, the PVA matrix doped with various content of SiO 2 nanoparticles showed an increase in the hydrophilicity, as the water contact angle with the film surface was found to decrease with increasing the SiO 2 content in the PVA matrix [29].While, SiO 2 nanoparticles were observed to enhance the hydrophobicity and raise the roughness of the PVDF-HFP films [30].Also, the optical properties and wettability of the polystyrene films were affected by the inclusion of SiO 2 in the matrix [31].SiO 2 was found to play a vital role in changing the wettability of polymer films [29,31].
Herein, novel PVA/CMC films reinforced with different amounts of SiO 2 are fabricated.In addition, the wettability and surface roughness properties of the blend matrix are investigated for the first time, as is the influence of various concentrations of silica on it.To characterize the functional groups of the prepared films, Fourier transform infrared spectroscopy was used.Moreover, the surface roughness and the water contact angle were investigated.Utilizing the absorption and transmission data from UV-visible spectroscopy, one can accurately estimate the optical parameters of PVA/CMC/SiO 2 films.This approach provides a reliable and efficient way to analyze these films, providing valuable insights to both academics and business experts.

Experimental and Characterization
PVA/CMC films were prepared by casting the solution.First, PVA (molecular weight (M η ) = 1 × 10 6 , QualiChem's company, India) and CMC (0.7°of substitution and M η = 1 × 10 5 ) powders, with a ratio of 80/20, were dissolved separately in distilled water.Subsequently, the polymer solutions were blended by adding the PVA solution to the CMC solution while stirring constantly at room temperature for 2 hr, until a homogenous mixture was achieved.Then, the prepared PVA/CMC blend solution was divided into five flaxes; one of them was pristine without additive, and the others were reinforced with xSiO 2 (x = 0, 1, 2, 3, and 4 wt.%) using probe ultrasound procedure.After the distribution of SiO 2 nanoparticles in the blend matrix, the mix was poured into Petri plates and left to dry at room temperature (25°C) for several days.The prepared samples with 0, 1, 2, 3, and 4 wt.%SiO 2 in PVA/CMC blend were lapeled as PCS0, PCS1, PCS2, PCS3, and PCS4, respectively.Finally, the prepared films with approximately a thickness of about 100 μm were utilized for measurements.The position and intensity of the chemical bonds of the films before and after the inclusion of various SiO 2 concentrations were recorded via Fourier transform infrared (FTIR) spectroscopy.A roughness tester (SRT-6600) was utilized to measure the surface roughness of the polymer films.This tester relies on a moving sensor on the film surface to identify a roughness profile curve and instantly record the roughness parameters.The wettability of the PVA/CMC blend films can be accurately determined by measuring the contact angles using the reliable Ossila Digital Goniometer (Model L2004A1, Sheffield, UK), with an accuracy AE1°.An ultraviolet-visible spectrometer was used to measure the blend films' absorbance both before and after SiO 2 was added.

Results and Discussion
3.1.FTIR, Contact Angle, and Surface Roughness Analysis.Figure 1 shows PCS films' FTIR spectra.The bond positions and assignments for the pristine PVA/CMC are presented in Table 1.
The broadband in the region 3,200-3,500 cm −1 is assigned to ─OH group.The fingerprint bands in the region from 1,500 to 400 cm −1 show the characteristics bond of PVA and CMC.The band observed at 1,070 cm −1 is related to C─O bond of CMC, and the same band also was assigned for PVA.The SiO 2 impact on the vibrational modes in terms of a reduction or increase in band intensity with increasing SiO 2 content was observed due to crosslinking with the blend functional groups.For the pristine sample (PCS0), the bond at 2,166 cm −1 was shifted to higher wavenumber at 2,167, 2,168, 2,169, and 2,169 cm −1 for PCS1, PCS2, PCS3, and PCS4, respectively.The bands at 957 and 856 cm −1 are assigned to the stretching of CH 2 and C─C bonds, respectively.These bands are slightly shifted with increasing SiO 2 concentration in the PVA/CMC film, as shown in Figure 1(b).The band at 920 cm −1 is linked to the C─C stretching band of PVA was vanished with the inclusion of higher content of SiO 2 nanoparticles, which might be due to the destruction of this bond and formation of the new bond Si─O─C [37,40].The band at 1,095 cm −1 , which is related to both PVA and CMC [41], ascribed to the C─O bond of the PCS0 sample, was shifted to 1,079 cm −1 after the inclusion of 4 wt.%SiO 2 .This is ascribed to the combination of the Si─O band of the silica at 1,060 cm −1 with the C─O bond of the polymer blend matrix [40].Besides the weak band observed at 1,234 cm −1 which attributed to the Si─O─Si asymmetric vibrations [36,42].In addition, the Si─O─Si stretching mode at 800 cm −1 at the higher content of SiO 2 nanoparticles testified to the presence of SiO 2 in the blend matrix, as mentioned elsewhere [36,40].The FTIR analysis results are conclusive; they show that the PVA/CMC blend and SiO 2 have a clear and specific interaction.These findings demonstrate the potential for this blend to offer unique benefits and applications in the field.
The interaction between the liquid and solid surfaces is highly dependent on surface-free energy, and it is the main parameter that influences the wetting property.The contact 2 Advances in Polymer Technology angle measurement, which indicates the wetting property's degree, can be used to explain the wetting characteristic.Surface wettability of hydrophobic material decreases with increasing contact angle, while surface wettability of hydrophilic material increases with decreasing contact angle [43].The contact angle value of drop-distilled water on the film surface was measured for PVA/CMC blend film and PVA/CMC films doped with SiO 2 .Figure 2 shows the average contact angle (θ), measured on both sides (left and right), of water droplets on the surface of the PCS blend films.The angle of contact decreases from 37.6°for PCS0 to about 29.3°, 23.2°, 21.2°, and 16.3°for PCS1, PCS2, PCS3, and PCS4, respectively, as the SiO 2 concentration increases in the blend film.This affirms the more hydrophilicity of the blend film after the inclusion of SiO 2 , owing to SiO 2 's high hydrophilicity [26].The reduction in contact angle is an indication of the increase in wettability with increasing SiO 2 concentrations.Consequently, micropores could be formed because of enhancement of the wettability and it may cause a change in the surface roughness.
The surface roughness for PVA/CMC blend films with the effect of various concentrations of SiO 2 was investigated, as shown in Figure 3. From the roughness curves, the roughness parameters were extracted, and Table 2 presents the results.It is crucial to note that R a signifies the mean height, R p is the maximum peak height, R q is the root mean square profile height, R v is the maximum valley depth, and R z is the average maximum height [44,45].
It is obvious that the values of R a , R z , R p , R q , and R v all increase with increasing SiO 2 concentration in the blend film.It confirms the rise in film roughness with increasing SiO 2 concentrations.This impact of SiO 2 nanoparticles on the surface roughness is consistent with previous observations for PVDF-HFP [30,46].PVA and CMC are hydrophilic polymers, in contrast to PVDF, which is a hydrophobic polymer.The contact angle of the PVDF film was found to increase with increasing SiO 2 concentrations, while here the contact      [44].The R sk values for the others, PCS2, PCS3, and PCS4, are positive and show an increase with increasing SiO 2 concentrations, which reveals the increase in the roughness of the film's surface.

Optical Properties.
The spectra (transmittance and absorption) of PVA/CMC films as a function of the incident light wavelength (λ) are displayed in Figure 4. Obviously, the absorbance of the blend films increases gradually with increasing the SiO 2 concentrations, as shown in Figure 4(a).
In addition to the shift in the absorption edge toward the higher wavelength region, indicating to the decrease in the bandgap of the blend films.The hump observed at about 276 nm is related to the π-π * transition [45].With a rise in SiO 2 concentrations, the transmittance of blended films goes down, as shown in Figure 4(b).This highlights the importance of controlling the concentration of SiO 2 to ensure maximum transmittance and, ultimately, optimal performance of the blended films.In the visibleregion around 500 nm, the transparency of the blend films decreases from 75% for PCS0 to about 73%, 72%, 70%, and 68% for PCS1, PCS2, PCS3, and PCS4, respectively.The addition of SiO 2 to the blend matrix causes an increase in the number of absorbed atoms and, of course, a decrease in the transmittance of light.The observed influence of SiO 2 on optical transmittance aligns with previous findings documented in the literature [31].The film absorption coefficient (α) is determined using the absorbance (A) and the film thickness (t) according to the following relation [47]: According to this, the optical parameters, which include E gd (direct-bandgap), E gi (indirect-bandgap), E U (tail-band-width, or Urbach energy), n (refractive-index), k (extinction coefficient), ε′ (optical dielectric constant), ε″ (optical dielectric loss), and σ opt.(optical conductivity), can be calculated using the following relations [33]: where B 1 and B 2 are constants, and C is the speed of light (3 × 10 8 m/s).As illustrated in Figure 5, the E gd and E gi are derived from the relation between ðαhυÞ 2 and ðαhυÞ 1=2 versus (hυ), Advances in Polymer Technology respectively.The E gd for the pure PVA/CMC blend film is about 5.52 eV, which is consistent with previous work [18,19].From Table 3, the E gd and E gi values slightly decreased with increasing the SiO 2 concentrations in the PVA/CMC blend film.

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Advances in Polymer Technology matrix.This behavior is related to the defects created as the SiO 2 is added to the blend matrix, and this result is in good accordance with the literature [20,48].The phenomenon could be associated with the interactions between the molecules of the blend matrix and the SiO 2 atoms.These interactions may form a hydrogen bond that creates localized states within the forbidden energy zone and reduces the distance between the valence and conduction bands.This disorder and defects created were affirmed by investigation of the tail width, Urbach energy (E U ), of the blend films using Equation ( 4) [49].The linear portion from the relation between ln (α) and (hυ), Figure 6(b), is the reciprocal of E U .
It is clear from Table 3 that the E U value increases from 0.84 eV for PCS0 to about 0.91 eV for PCS4, confirming the blend matrix's increasing disordering and bandgap decreasing.
According to Equations ( 5) and ( 6), n and k values are computed regarding λ, as shown in Figure 7. Evidently, n and k both rose as SiO 2 concentrations increased and fell as incident light wavelengths increased.
As the SiO 2 concentration increases in the blend matrix, the number of atoms colliding with incident light increases and the reflectivity of the films increases as well.As a result, the refractive index rises along with the slowing of light velocity inside the blend matrix.On the other hand, the k value represents the loss of energy caused by light scattered or absorbed by the material [50].As shown in Figure 7(b), it showed a normal behavior in the UV region, as it decreases sharply as it is related to the bandgap region, which has high energy sufficient to be absorbed and the loss caused by scattered or absorbed light will be less.

Advances in Polymer Technology
The ε r and ε i as a function of the hυ are illustrated in Figure 8.Both optical parameters are increased with increasing the SiO 2 concentrations in the PVA/CMC blend films.An increase in ε r value is directly proportional to the higher density of states within the bandgap, resulting from the increased concentration of SiO 2 [51,52].In addition, the ε i value increased with increasing SiO 2 concentration, and the absorption band at the higher photon energy region shifted toward the lower photon energy.This is explained by the fact that as SiO 2 concentration rises, the number of free charge carriers in the matrix also rises [51].
The optical conductivity (σ opt. ) dependence on photon energy is displayed in Figure 9.It shows an increase in σ opt.with increasing SiO 2 concentrations, which could be due to the rise in charge carriers in the blend films.
The SiO 2 impact on the σ opt. of PVA/CMC films results from the transfer of charge between the blend's molecules and SiO 2 [53].The interstitial spaces between the matrix chains are filled by SiO 2 and form a segregated network [54].Hence, the optical conductivity increases as well.

Conclusion
Probe sonication and casting solution techniques were utilized for preparing the blend matrix of PVA/CMC with various amounts of SiO 2 .The FTIR analysis revealed the interaction between the blend matrix molecules and SiO 2 nanoparticles.The contact angle and surface roughness parameter investigations confirm the modification of the PVA/CMC surface after the inclusion of SiO 2 , where the surface roughness and surface wettability of the PVA/CMC matrix were increased.This is related to the hydrophilic of the SiO 2 nanoparticles.The optical analysis showed a slight decrease in the blend film transparency with increasing the SiO 2 amount, and a redshift was observed in the absorption edge, which confirms the reduction of the optical bandgap energy.The decrease in transparency and increase in film absorption raise their possibility of being used in UV-shielding applications.Th optical bandgap decreases from 5.52 eV for pure PVA/CMC to 5.17 eV for the PVA/CMC/4 wt.% SiO 2 .This drop was related to the defects in the materials, and the refractive index rises due to increasing matrix density.The prepared current matrix, PVA/CMC/SiO 2 , is considered a potential candidate for optical applications.

FIGURE 2 :FIGURE 3 :
FIGURE 2: The correlation between the concentration of SiO 2 and the contact angle in the PVA/CMC films.

TABLE 1 :
FTIR bands assignment of PVA/CMC blend film.