Study the effect of cobalt chloride (CoCl2) on the structural, optical, and electrical properties of polymer electrolyte (PVA-CoCl2) films

A study of non-ionic polymer Polyvinyl Alcohol (PVA) in pure and transition metal salt Cobalt Chloride (CoCl2) incorporated films with different weight percentages to change the optical, electrical, structural, and chemical structure also to make electrically conductive. To prepare the material in terms of film desired weight percentage of polymer PVA alone and for doped polymer different weight percentages of transition metal salts are dissolved in deionized water at a certain temperature and a solution cast technique is followed to get the desired thickness of film. Obtained films were transparent and achieved micro-thickness film. Experimentally confirmed for betterment in optical property to enhance in terms of absorbance, transmittance, direct and indirect energy band gap, extinction coefficient, reflectance property, refractive index, number of carbon clusters, and dielectric constant. The prepared film thickness is measured by using a Mittometer. Surface morphology studies are achieved by SEM analysis in terms of top view and sectional view also thickness of the sample is confirmed. Surface roughness and Maximum Height of the Profile are confirmed by profilometry studies. Electrical property is measured to find the desired range of IV value and to understand the sample behaviour as a resistor.


Introduction
Polyvinyl alcohol (PVA) is considered to be one of the most significant polymeric materials due to its wide range of applications in the industry and its relatively low manufacturing cost.Polymeric materials are a subject of great interest in scientific and technological research owing to their ability to be customized to meet specific requirements for a variety of applications.This is primarily due to their lightweight nature, excellent mechanical strength, and optical properties.Polymers have the potential to generate novel electronic levels within the forbidden gap of the electronic band structure.As a result, they transform from being insulating material to possessing electrical conductivity.This phenomenon presents various opportunities for the utilization of these materials in potential applications, such as the production of integrated circuits, optoelectronic devices, sensors, ion-detecting devices, solid-state batteries, which is capable of resisting water and thus inhibiting the entrance of moisture and other technological applications.

Synthesis
To obtain the desired weight percentages of PVA-CoCl2 sample films with concentrations of 0%, 5%, 10%, 15%, 20%, 25%, and 30% the technique of Solution cast was employed.The process of sample preparation involved taking 25 ml of deionized (DI) water in a beaker, which was then heated to 50°C using a hot plate.Subsequently, 4g of PVA was measured and added to the DI beaker, which was then stirred at 300rpm using a magnetic stirrer for approximately 8 hours, maintaining a temperature of around 50°C, just below its glass transition temperature.The resulting sample, with a specific consistency, was poured into a glass petri dish with a diameter of 95mm and left to dry for a period of 2-3 days at 50°C.Once the sample had solidified, it was peeled off from the petri dish and sealed in zip cover bags, after which it was subjected to desiccation for approximately 1 week.The film obtained was then cut into squares with a desired area of one square centimetre, it conduct further experimental characteristics.

Sample thickness
The physical property, thickness and of the sample was found using Mittometer.The sample thickness obtained between the ranges 70µm to 100µm was measured using a Mittometer as shown in figure 1 and the values in Table 2.

Optical Properties
The optical properties were studied using UV-visible NIR spectroscopy using Quartz tungsten Halogen lamp as a source for pure and composites between 200 nm to 1500 nm wavelength range.The transmittance property has decreased from 92% to 45% evidencing an increase in absorbance property.Reflectance percentages decreased from 7 to 0.1% is found highest in 30% weight percentages as shown in figure 2a, 2b, 2c respectively.The optical band gap energy Eg is calculated using Tauc's equation, Absorption coefficient α, ℎ = (ℎ −   )   = 2.303.( −1 ).() −1 where n=0.5 for Direct / n=2 for Indirect Energy, T is transmission, t is thickness of the sample, ℎ is Plancks constant,  frequency of source.Extinction Coefficient κ, refractive index η, Carbon Cluster Number Ν from 5 6 found tailored from pure to doped PVA-CoCl2 films as in figure 3. 7 and values are found in Table 1.The refractive index was found to be increased, which helps in low scattering of the lattice materials, and the angledependent scattering profile results in a reduced translucent appearance. 8Carbon cluster is found to 3 know the elemental composition and excitation levels within the molecule using equation given by Robertson's and O'reilly 9 .analysis indicates that the amalgamation of the PVA -CoCl2 sample is homogeneous, thereby minimizing agglomeration.Furthermore, it reveals a decrease in the amorphous characteristics with varying concentrations.Additionally, the thickness from a lateral perspective is assessed through scanning electron microscopy, which correlates with the aforementioned device measurement as in figure 4. 10 The surface roughness can be visualized and linked to surface profilometry.Table 2 Measured thickness using a Mittometer and SEM.

Surface Profilometry
Surface thickness was found using Surface Profilometry using Surface Profiler-Bruker 3D Noncontact Profiler Contour GT device.

Sample
Thickness Average Roughness Ra to know amorphous nature of sample decreased with increased concentration 11 as shown in figure 5 and the values in Table 2.

DC Electrical
DC Electrical property studies were done using Probe Station -Cascade Microtech Summit 12000AP Current versus Voltage using probe station in vacuum for the temperature range -50 0 C to +190C and voltage range -100V to +100V and checked for the current correlation.The electrical properties is studied using DC Conducting property.The current value has increased from nano to micro range with increased concentration of dopant.The graph nature of current I versus Voltage V is studies to know resistance and resistivity of the material.Hence conductivity has plotted corresponding to doped percentages in figure 6.The resistance R, resistivity ρ, conductance σ obtained values are tabulated in Table 3.

Conclusion
The PVA -CoCl2 sample with varying concentrations of dopant was economically, timely, and qualitatively, homogeneous film was obtained.UV studies proves band bap energy decreases resulting in enhancement of absorption for enhancing of photons jump within the level enhancing Π-Π* for transition metals.Decrease in the amorphous characteristics with varying concentrations proving the surface roughness using SEM morphology and Surface profilometry average roughness enhancement.Additionally, the thickness plays important role in calculating many parameter is confirmed from a lateral perspective through scanning electron and Mittometer.The significant value of conductivity, resistivity using DC electrical conductivity shows the material best suited for electrical devices.PVA-CoCl2 can be used as coat resistant for preventing moisture penetration on the surface.

Figure 1a .
Figure 1a.Synthesis process flow.Figure 1b.Film obtained by Casting. Figure 1c.Measurement of film thickness using a Mittometer respectively.

Figure 2a ,
Figure 2a, 2b, 2c.The plot of Transmittance, reflectance and absorbance respectively for Pure PVA and different weight percentages of PVA-CoCl2.

Figure 3 .
Figure 3.The graph for indirect -direct band gap, absorption coefficient, extinction co efficient, refractive index for Pure PVA and different weight percentages of PVA-CoCl2.

Figure 4 .
Figure 4. SEM images of Pure PVA and different weight percentages of PVA-CoCl2 are illustrated in both the top and side views.
Figure 5. Surface profilometry for different doped percentages to know surface roughnes.

Figure 6 .
Figure 6.The graph for DC conductivity IV studies for Pure, 5% and 30% PVA-CoCl2.Different sample at different Voltage range and temperature range at vaccum chamber, room chamber and two cycle multiple run respectively.
Authors has been acknowledged Kuvempu University for its provision of deionized water and space for the purpose of fabrication.Dr. Praveen K C, a Scientist and Engineer in the Laboratory for Electro-Optics Systems (LEOS) within the Indian Space Research Organization (ISRO), has been recognized for conducting UV NIR Spectroscopy studies.The Microelectronics and MEMS Laboratory, situated within the Department of Electrical Engineering at IIT Madras, has been commended for their involvement in the characterization of SEM, Profiler, and DC measurements as part of the INUP Program.

Table 1 .
Summary of optical Property obtained from UV -NIR Spectroscopy for pure and different weight percentages of PVA doped films.
Surface morphology studies and thickness of the sample were studies using Table top Scanning electron microscope (SEM) SNE4500M, with 5000V and magnification of 1000 times.Morphology 4

Table 2 .
Summary The sample roughness is understood by the surface profilometry image.This evidences the SEM morphology to know surface smoothness decreased and increase in average Roughness of the surface, 1300 (2024) 012017

Table 3 .
Summary of electrical properties of PVA-COCl2 films at different temperature and voltage between -20 to +20 V.