Effects of MWCNT Nanoparticle Doping on Optical and Structural Behavior of Polyvinyl Alcohol

INTRODUCTION

The main objective in the development of composite materials is to produce materials with improved mechanical and physical qualities that aren’t found in each of their components. This is because of their extraordinary capacity for mutation and perfection in these attributes, which has driven the world’s current development of these compositions into an unending race because of the pressing demand for these unique and distant attributes on the original restricting [1,2]. It is only recently that the majority of polymers have been used to produce inexpensive products with simple functionality. However, because technology was developing so quickly, some industrially used materials had to be replaced with better ones. Consequently, in a number of applications involving high temperatures and pressures, polymers have replaced iron and aluminium [3,4]. The potential of polymer composites to produce materials with qualities like excellent flexibility, cheap cost, and low-temperature manufacture is unsurpassed [5,6]. It is possible to classify the polymers as natural or industrial. Natural polymers include things like rubber, cellulose, proteins, and starches. Among the several synthetic polymers are poly(vinyl chloride), polypropylene, nylons, polyethene, polyvinyl alcohol, polyesters, polyacrylamide, and polycarbonate [7-9]. Small but mighty, the word “nano” has become increasingly popular in recent years and has the power to alter the course of history. Nanotechnology is one of the most significant scientific areas of our time because it integrates knowledge from physics, chemistry, biology, medicine, informatics, and engineering. Though yet in its infancy, this field of technology has a great deal of promise to provide essential breakthroughs with real-world uses. Tools and processes related to nanotechnology can be used to produce and control new nano and biomaterials as well as nano devices [10,11]. 

The polymer known as poly(vinyl alcohol) (PVA) is semicrystalline. Its qualities include a high harge storage capacity, superior mechanical and thermal stability, and high dielectric strength [12,13].The unique qualities of carbon nanotubes (CNTs) include excellent charge transmission, high mechanical strength, and thermal stability. The host matrix’s characteristics were significantly improved when a tiny quantity of CNTs were added to the polymer [14].

The principal objective of the current work is to examine the synergistic effect of MWCNT nanoparticles on the optical and structural (morphology) properties of PVA. The world has become more industrialized, especially in the area of electronics, and many electronic components require improvement to solve various problems with optoelectronic devices. These are crucial things to remember. The study aims to make new films that can be utilized for these purposes. 

MATERIALS AND METHODS

Sigma-Aldrich provided the polyvinyl alcohol (PVA), which has a molecular weight 146000. The source of pure multi-wall carbon nanotubes (MWCNTs) was Nanothinx (Greece). CNTs are 90 per cent pristine, with an outer diameter of 10–30 nm and a length of 10–30 μm. After verifying the purity of each chemical, we melted one gram of each and discovered that the melting points were highly near.

To prepare the solution, 5g of the PVA was dissolved in 130 mL of dissolved in water, After this, the mixture is put on the magnetic mixer and stirred well to dissolve the substance. Then MWCNTs added is to a solution for the purpose of mixing different proportions (0.01, 0.02 and 0.03) % gm., PVA mixed with MWCNTs for 4 samples as shone also placed on the magnetic mixer and stir well to dissolve the material within 25 minutes for each sample. 25 ml of the solution was taken and placed on the sedimentation surface glass, after that the films were prepared by spin coating at 2000 revolutions per mint. Ultimately, the films were meticulously removed and preserved in a dust-free area in preparation for additional research. 

In addtion, to ensure the purity of the materials used, we melted 1 gm of each substance. The result was that the melting point for each substance was very close to the degree indicated in the information tape attached to each package.

Subsequently, studies were conducted to examine the optical characteristics and surface morphology of the thin Nano composite films.

Digital instruments (Inc. BY2000) are used to first capture Atomic Force Microscope (AFM) micrographs in order to observe the surface roughness and topography of deposited thin films. Common characteristics derived from AFM height pictures include grain size and root mean square (RMS) roughnessfor topographic mapping, there are three main approaches: touch, non-contact, and intermittent tapping or contact. An AFM’s tip is its most important part because of its Nano scale radius of curvature. A micro-scale cantilever, to which the tip is attached, senses the Van der Waals interaction and additional forces acting on the tip and sample. A Shimadzu UV-vis 1800 double-beam spectrophotometer, It recorded the transmittance (T) and absorbance (A) spectra of the generated samples over the 200–1200 nm scanning wavelength range at room temperature. A sample of the same type of glass is also used as a reference to cancel out the effect of the glass where it is put in front of the falling rays and they fall perpendicularly on the sample. the computation of the films’ absorption coefficients at various wavelengths using transmittance and reflectance data. The values of the transition, the absorption coefficient (α), the direct energy gap (), the extinction coefcient (K), the reflectance (R), and the refractive index (n) were determined based on the measured A. The produced composites [15–22] were computed using the following formulas:

Where t, B, hv, and r stand for the thickness of the film, incident photon energy, and an electronic transition type-related parameter, respectively.

In addition, the ratio of a material’s absorbed light intensity (I_A) to its incoming light intensity (Io) is known as absorption [23].

The transmittance of a film is determined by dividing its incident ray (Io) intensity by its transmitting ray (IT) intensity, as expressed in the following formula [24]:

RESULTS AND DISCUSSION

The tests (AFM) of the Nano films for both pure (PVA) and doped (MWCNTs) films made by spin coating demonstrated a consistent almost surface shape, as shown in Fig. 1. Where it is evident that the roughness rose as the doped ratio increased. The average grain diameter likewise indicates the same tendency that the root mean square (RMS) did as the doped ratio increased. Table 1 suggests an enhanced crystalline structure with a higher percentage of carbon nanotubes, leading to larger particles and rougher surfaces. Fig. 2 illustrates how, compared to the pure PVA film, its surface has more pits and pores and is less smooth. Fig. 3 shows the uneven surfaces, with numerous strewn and hump-shaped grains. On the PVA/MWCNTs mix surface, Additionally, brilliant granules of different sizes and shapes are embedded in a quasi-homogeneous nature. MWCNTs are primarily responsible for these grains. As the MWCNT’s weight percentage is raised to 3%, as seen in Fig. 4, the diameters of these agglomerations grow. Previous research documented similar traits [25,26].

It aims to characterize and study the optical properties of Nano composites (PVA-MWCNTs) Nano composite is to know the effect of doping multi wailed carbon nanotube nanoparticles on optical properties of PVA. This optical study includes the optical transmittance and absorption of Nano composites at room temperature, as well as calculating absorption, refractive and extinction coefficients.

The chemical makeup, crystal structure, incident photon intensity, film thickness, and surface shape all affect optical absorption spectra. At ambient temperature, the absorption spectrum of thin PVA-MWCNTs sheet Nano composites with varied MWCNT concentrations was observed for the 285–400 nm wavelength range. 

Fig. 5 demonstrates how the wavelength of the (PVA:MWCNTs) Nano composites affects the optical absorption. This spectrum indicates that all coatings exhibit more excellent UV absorption. After that, absorption reduces before it reaches the visible spectrum because atoms cannot interact with the energy of the incident photons. The material absorbs the photon when it gets closer to the fundamental absorption edge due to interactions between the falling radiation and the material beneath it. We find that when the weight ratios of the nanomaterial increase, the absorption decreases. This is the effect of free electrons absorbing incident light. This outcome agrees with the findings of the other researcher [27]. Furthermore, at about 330 nm, a further absorption edge associated with the n→π* inter-band PVA transition is observed [17]. Compared to UV absorption at 285 nm, MWCNTs exhibit moderate absorption in the visible region [28].

Fig. 6 shows that the transmittance for all samples increases with the increasing concentration MWCNTs nanoparticles and the reason for this rise is because the grains’ crystal sizes have grown [29]. As for the higher transmittance in beginning the wavelength range of the spectrum High in the near Ultraviolet range at from (200-400 nm), this is due to the absorption of light photons.  Optical transmittance increases due to the regularity of the granular distribution, which is accompanied by a decrease in light scattering. This result agrees with the result of the other researcher [30]. 

Fig. 7 represents the relation between the reflectivity with wavelengths for pure PVA and doped with different ratio of MWCNTs. the incident photon with the variation of different thickness. With an increase in input photon wavelength across all films, the reflectance decreases quickly and reaches its maximum value at the wavelength of the film energy gap. This could function as a marker for the material absorption edge. These results are in agreement with reference [30].

All thin film values (α) are more than 10⁴ cm^-1 in the ultraviolet region. Fig. 8 illustrates how the absorption coefficient values of pure polymer and its doping decrease as the doping ratio concentration increases. The image shows that the absorption coefficient and absorbance spectrum act similarly. This is because of how they are related, as shown in equation 1.

Using the formula n = C / v, we may determine the refractive index n at the speed of light in a vacuum instead of its speed in a substance. The morphological structure and the type of material have an impact on the n [31]. Fig. 9 shows that with the beginning the wavelength the refractive index will for the sample pure PVA Larger than other membranes, the uniform dispersion appears when the curve begins to decline ‘and this is due to the decrease in absorption. We can see from this figure that when the concentration of nanoparticle weight percentages (MWCNTs) in polymer increases, the refractive index values fall. As MWCNTs was loaded alone with PVA, The shape of the refraction index curve for different parameters is similar to the reflectivity curve because the reflectance is associated with refraction index according to the same relationship. This result agrees with the result of the other researcher [32]. 

The attenuation of an electromagnetic wave travelling through a material is indicated by the extinction coefficient (K_O), which measures the absorption energy in the thin film material. The density of free electrons in the material and structural flaws affect the values of (K_O). Fig. 10 illustrates the correlation between the wavelength and extinction coefficient of PVA and PVA: MWCNTs thin films deposited. For all prepared samples, it is generally evident that the extinction coefficient (K_O) changes as the wavelength (λ) increases. The extinction coefficient (K_O) falls for every prepared sample as the number of MWCNTs increases. Generally speaking, the behaviour of (K_O)is comparable to that of α. These outcomes concur with reference [33].

Energy gaps have been calculated using equation (2) for the allowed and banned indirect transition band. Specifically, the predicted indirect transition band optical energy gap is allowed when r = 2, but it is prohibited when r = 3. Fig. 11 shows the relationship between the absorption edge (αhv)^1/2 for PVA and PVA. One may determine the energy gap for the indirect transition in MWCNTs thin films by drawing a straight line at the value of (αhv)^1/2 = 0 from the upper section of the curve towards the (x) axis. The resulting values are shown in Table 2. The optical energy gap values decrease as the weight percentages rise. In this case, the transition happens in two phases, with the electrons going from the valence band to the local levels and subsequently to the conduction band as a result of the weight % being increased. This is explained by the production of site levels in the forbidden optical energy gap. The heterogeneity of films that is, the fact that electrical conduction depends on additional concentration explains this phenomenon. The decrease in the direct energy gap can be explained by creating electronic pathways in the polymer, which enable electrons to go from the valance band to the conduction band when the weight proportion of PVA and PVA: MWCNTs increases. The findings of the second researcher support this assertion [34].

The primary cause of this fluctuation in  (4.181 to 4.167 eV) is the expansion of the generated energy states between the HOMO and LUMO levels of the host blend’s energetic band gaps. Additional variables leading to the decrease in the  value are the increased density of voids, disorder, and flaws in the composite mixes due to the filling procedure [35].

CONCLUSION 

The following conclusions can be drawn from the PVA that was examined and doped with MWCNTs manufactured using the spin coating technique: The surface morphology of thin films was investigated using the atomic force microscope (AFM) technique. The findings showed that as the concentration of MWCNTs grew, the prepared average roughness, root mean square (RMS) values, and average grain diameter all increased. The inclusion of CNTs improved the qualities of PVA. When compared to absorption in the UV area at 265 nm, MWCNTs exhibit considerable absorption in the visible range.  Moreover, noteworthy outcomes were observed about the decrease in absorbance with a rise in filler content, the increase in transmittance with an increase in MWCNTs, and the increase in reflection decrease with doping. The absorption coefficient, extinction coefficient, and refractive index all decrease with an increase in MWCNT content. Multi-wall carbon nanotubes (MWCNTs) and polymer (PVA) have the characteristics that make them the best choices for gas sensors.

CONFLICT OF INTEREST

The authors declare that there is no conflict of interests regarding the publication of this manuscript.