The spectral properties and dispersion parameters of electrospun nanofibers (Poly vinyl alcohol/ Poly acrylamide)

nanofibers based on polyvinyl alcohol (PVA), polyacrylamide (PAAm), and a PVA-PAAm blend (50/50 wt.%) were effectively made a room temperature(RT) and a voltage of (12kV).The products were studied using Field Emission Scanning Electron Microscope (FESEM), X-ray diffraction (XRD),Fourier-transform infrared spectroscopy(FT-IR) and Ultraviolet visible (UV–Vis) spectroscopy. The result of FESEM analysis showed that the polymer PVA, PAAm, and blend samples produced a random distribution of fine fibers at an average diameter of (214.12, 317.1, 157.65) nm with a smooth surface. In addition, the FESEM images demonstrate the fibres' suitability for use in gas sensing applications due to their branching fibres and porosity surface. XRD showed that the film polymeric of PVA, PAAm polymeric blend PVA-PAAm was seen to have a semicrystalline nature. According to the FTIR analysis, the PVA and PAAm networks in the PVA-PAAm polymer nanofibers were entangled due to the powerful hydrogen bond contact between the PAAm and PVA chains. Observed around (3473.79 and 3414) cm -1 were attributed


Introduction
Polymers have quickly become an essential component of contemporary life.This is because of their versatility and low cost, low operating costs, simple processability, and desirable chemical, physical, and optical qualities [1,2]: Each molecule in a polymer is made up of thousands of atoms held together by covalent chemical bonds, and the molecules in a polymer are attracted to one another by forces that vary depending on the kind of polymer [3,4]: Due to their advantageous blend qualities, biomedical and pharmaceutical devices should utilize two polymers that can create hydrogen bonds when blended [1].

‫اإلنكرشوٍَح.‬ ‫األخهضج‬ ‫فً‬ ‫نالسرخذاو‬
The PVA fiber has high tensile and shear strengths, tensile modulus, and wear resilience due to its maximal rigid lattice modulus.It is a synthetic polymer that comes in the form of a granular powder that is odorless.The PVA has attracted an increasing amount of interest in the biomedical area because to the fact that it is bioinert.Many researchers have investigated the possibility of employing the PVA as a filler or in cross-linked products [5][6][7].In addition to its many other applications, it has seen used extensively as a thermoplastic polymer for the production of non-toxic, harmless, and living tissues [3,8].
Polyacrylamide (PAAm) is a material that dissolves in water with a wide range of industrial flocculant applications.The PAAm and its derivatives have great attention in recent years due to their high molecular weight, their ability to dissolve in water without resembling a monomer, and their non-toxicity.Their copolymers with other hydrophilic monomers and their metallic salts are used in many applications, including mining, water treatment, and others [9].The PAAm may be dissolved in various Polymers like polyethylene glycol (PEG), polyvinyl alcohol (PVA), and carboxymethyl cellulose(CMC) [5,10,11].
Blends of polymer (PVA) with polymer (PAAm) have been determined through mechanical analysis in a variety of ways by many researchers: Gaurang Patel and Mundan B. Sureshkumar, two of the researchers, have conducted a study on the miscibility of PVA and PAAm in various proportions by employing the solution-cast technique.They have discovered that variations in FTIR, UV-Vis, TGA, SEM, and mechanical measurements indicated the interactions between the two polymers [12].Eldin et al. studied the miscibility of PVA with PAAm in different proportions using the solution-cast method and gamma radiation up to 100 kGy.Visual inspection and reflectance tests demonstrated that the PVA/PAAm blends are miscible throughout a broad composition range [13].The X-ray diffraction examination confirmed the creation of a complex between the polymer mixture and the Ag NPs [14].
Electrospinning is a technique that is being utilized in the present study, and it is the way that is most often employed for the manufacturing of nanofibers [15,16] because of the ease its of use and capacity to work with several polymers .The electrospinning process is used to create fibers from a wide variety of polymers, both synthetic and natural, including biopolymers, with diameters ranging from tens of nanometers to a few micrometers [17,18].In this study, two existing polymers were blended to create a new polymer, which was based on Poly(vinyl alcohol)/Poly (acrylamide) (PVA-PAAm) and compared among the prepared samples for optical and communication applications.

Materials
The particulate polymer PVA used was bought from Himedia, India, and had a high purity level of 99.0% and M W =(85,000-126000) g/mol.
Polymer PAAm was produced commercially by British Drug Houses (BDH) and had an extremely high purity level of 99.99% and M.W = 5*10 5 g/mol.

4.2.Purification of PVA, PAAm, and PVA-PAAm nanofibers
A PVA of 1g was dissolved in 20 ml of purified water with constant agitation for 1.5h at a 50 o C. The solution PAAm was prepared by adding 1g to the blend and continuing to stir it for 2h at 50 0 C, albeit in intermittent doses.The process was repeated many times until a sufficiently thick liquid resulted.To get a suitable polymer combination, a PVA-PAAm (50/50 wt.%) ratio was used.The procedure, which took 2h, requires constant mixing by swirling until the fluid become homogenous.

4.3.Electrospun
The ready-to-use mixtures were transferred into a 2 ml pipette using a metal capillary needle with an interior diameter of 0.5 mm.The electrospun procedure was performed in a temperature-controlled environment at a flow rate of 0.5 ml per hour using a hypodermic pump.The aluminium foil-covered cylinder that was used in the production of the electrospun nanofibers rotated at a rate of 1679 rotations per minute.The needle tip was positioned 10 cm away from the drum, and a voltage of 12 kV was applied.This surface of electrospun nanofibers was analyzed using a FESEM.Patterns of XRD were taken using ( 0.1542nm).The chemical composition of the nanofibers mats was investigated by FTIR spectroscopy at RT with a spectrometer (Thermo Nicolet, Nexus670, USA) that has a spectrum range of (4000-400)cm -1 and a UV-Visible Spectrophotometer(Shimadzu, UV-1800A) that measures light at a frequency of (200-1100)nm.

Spectroscopy the Fourier transforms infrared (FTIR)
The ion peaks that are associated with the vibrational frequencies that occur between the links formed by the atoms that make up the substance serve as an important fingerprint in an infrared spectrum.Due to the unique composition of each material, no two substances will have the same IR range.Because of this, IR spectroscopy can be used to identify (qualitatively analyze) any kind of substance [21].Fig. 4 shows the FTIR spectroscopy of the pure PVA, PAAm, and blend PVA-PAAm nanofibers.The spectrum that was recorded reveals distinctive bands that are caused by oscillations in the functional groups caused by elongation and twisting of the groupings of the produced film.
The characteristic peaks of PVA locate at 3423.20 cm -1 , 2895 cm -1 , 1730 cm -1 , and 1141 cm -1 in the spectrum of PVA [11].Bands at 1730 cm -1 C=O stretching and 1141 cm -1 were attributed to C-O bending; a broad, very powerful band was observed at 3423.20 cm -1 , which was attributed to the O-H and N-H stretching vibration and indicated the presence of O-H hydroxyl groups in the pure PVA nanofibers [12].The FTIR spectrum of PAAm exhibits a band at 3105 cm -1 , which has been assigned to symmetric and asymmetric stretching vibrations of N-H and O-H, bands at 2960 cm -1 have been assigned to symmetric and asymmetric stretching vibrations of C-H, bands at 1662.63 cm -1 C=O stretching and 1450.46 cm -1 have been assigned to C-H bending.Additionally, bands at 1328 cm -1 C-H bending and 1110.9 cm-1 C-O stretching [9].Fig. 4 demonstrates the FTIR spectra of pure PVA and PAAm nanofibers and blend PVA-PAAm nanofibers.The vibrational bands at 3423.20cm -1 and 3105cm -1 assigned to O-H and N-H bending of pure PVA and PAAm nanofibers is shifted to 3473.79 cm -1 and 3414 cm -1 , the FTIR analysis of the PVA-PAAm hydrogel reveals that the PAAm and PVA networks are strongly hydrogen-bonded to one another at the N-H of PAAm chains and the O-H of PVA chains [11].

Optical Properties
Fig. 5 shows absorption patterns in the ultraviolet and visible ranges of the polymer pure PVA, PAAm, and PVA-PAAm blend.These spectra were obtained in the (200-1100) nm wavelength range at RT.These spectra were taken at RT and span from (200-1100) nm in wavelength.All of the coatings have strong UV absorbance and minimal Visual absorption, as is evident.The subsequent explains for this observation is as follows: Photons incident on a material at long wavelengths are not absorbed because they are insufficiently energetic to interact with atoms; photons incident on a material at lower wavelengths (near the basic absorption edge) interacting with the substance, which results in absorption.When a molecule consumes energy, a specific type of transition takes place in which the electron is boosted from an occupied orbit (σ, n or π) to a non-occupied orbit (σ*or π*) with a high energy level.Transitions (n -π*) or (π-π*) create a peak in the UV-Vis band, indicating the presence of C=O and C=C of unsaturated bonds primarily of the polymer mix; the energy gap is largely determined by transitions (π-π*) transitions in particular [22][23][24].The formula that was used to determine the absorption coefficient α(cm) -1 is denoted by equation 1 [25]. (1) The α(cm) -1 vs (eV) of the polymer pure PVA, PAAm, and PVA-PAAm blend are shown in Figure 6.It may be inferred by ion transformation is unlikely since ion absorption is excellent at high energies but rather poor at low energies.Absorption coefficients below 10 4 cm -1 suggest a high probability of indirect transfer [26].It is possible to see the shift in the band gap energy by observing the absorption edge of the doped mixture; this shift is caused by the varying degree of the presence of semi-crystallinity within the polymer material.Energy band gaps for nanofiber films were calculated using the Tauc equation 2 [27].

( )
In both kinds (allowed and forbidden), the intercept of the extended linear component of the parabola was used to calculate the indirect optical energy gap for nanofiber sheets made of pure PVA, PAAm, and PVA-PAAm versus the photon energy at , as shown in Figs.7  and 8, respectively.The goal was to measure the depth of the indirect optical energy gap.In Table1, we can see the optical band gap values for all of the samples, as shown in Table 1.Polymer nanofiber optical characteristics might be affected by a change in ion structure [28,29].The formulas (3and 4) for determining the refractive index (n) and the extinction coefficient (k o ) are provided below [27]: Fig. 9 shows the wavelength-dependent refractive index (n) of PVA, PAAm, and PVA-PAAm nanofibers.It can be seen that as the PVA-PAAm increases the (n) increases.
This unusual behavior may be attributed to the increasing in the concentrations of nanofibers.Light with a high refractivity in the ultraviolet area will interact with a sample, increasing the (n) values of the sample.Fig. 10 shows how the (K o ) of PVA, PAAm, and PVA-PAAm nanofibers vary with wavelength, optical absorption, and photon dispersion in the PVA-PAAm polymer blend increase.The increases in the PVA-PAAm polymer blend are accompanied by increases in the (K 0 ).This property may be associated with the high absorbance of nanofiber samples, which leads to a high (k o ) of nanofibers at UV wavelengths.Since the nanofiber α(cm) -1 is almost constant from the visible to the nearinfrared spectrum, the nanofiber (K o ) likewise increases with increasing wavelength.

Dispersion Parameters
Dispersion parameters were examined and diagnosed using the Wemple DiDomenico model.The values of were calculated using the formulas (5,6,7) [30].Taken from a graphic showing the relationship between and in Fig. 11, used the and the to determine .The Table (2) the energy gap band was calculated (the approximation relation ) using the Tauc relation and the Wemple-DiDomenico estimate had similar values, the findings are consistent with previous studies [30].

Conclusion
Electrospinning the polymers PVA, PAAm, and blend PVA-PAAm samples yields a heterogeneous of fine fibers with average diameters (214.12,317.1 and 157.65) nm and a smooth surface, as shown by FESEM.XRD showed that the film polymeric of PVA, PAAm polymeric blend PVA-PAAm is displayed to have a semicrystalline nature.The FTIR observation indicates the PVA-PAAm networks are strongly hydrogen-bonded to one another of PAAm chains and PVA chains.According to the predicted optical energy gaps of indirect allowed and forbidden from the absorption spectra, the energy gap band decrease of blend (PVA-PAAm).The calculated energy gap by Wemple .

Table 1 :
Optical indirect energy gap (allowed and forbidden) for the prepared nanofibers.
-DiDomenico was compatible with the value of the optical energy gap calculated by the Tauc relation and Urbach energy values increased.
eV EU