Structural and Optical Properties of PMMA-MgO Nanocomposite Film

This study investigates the structural, morphological, and optical properties of poly(methyl methacrylate) (PMMA) films incorporated with magnesium oxide (MgO) nanoparticles. The PMMA-MgO polymer nanocomposite (PNC) films were fabricated via solution casting method using varying weight percentages (1-4 wt%) of MgO nanoparticles. X-ray diffraction analysis confirmed the integration of MgO nanofillers in the PMMA matrix. Fourier transform infrared spectroscopy revealed interactions between PMMA and MgO nanoparticles. Atomic force microscopy demonstrated increased surface roughness in PNC films with higher MgO loading. Optical characterization using UV-visible spectroscopy showed enhanced absorption in the UV region and a noticeable peak at 280 nm due to MgO nanoparticles. The refractive index of PMMA-MgO PNCs increased with rising MgO content while the optical bandgap marginally decreased. The study highlights the potential of PMMA-MgO PNC films for advanced optoelectronic applications requiring high optical transparency and tuneable refractive index.


Introduction
The capacity of transparent polymer nanocomposites to display a wide range of optical features, such as tailored emission/absorption characteristics, varied refractive indices (both high and low), and strong nonlinear optical properties, has attracted a lot of attention [1].This heightened interest is rooted in the promising potential for optoelectronic applications [2].Typically, these nanocomposites are crafted by integrating metal oxide nanoparticles (NPs) into a transparent polymer matrix, such as polymethyl methacrylate (PMMA).The polymeric component contributes essential attributes like processability, transparency and flexibility, while the inclusion of NPs imparts desired thermal, electrical and optical properties [3]- [6].Demonstrating their technological and economic advantages, polymers have made significant strides in diverse fields, including automotive, chemical sensors and electronics [7]- [9].The fusion of metal oxide NPs and polymers has become a focal point for scientists, offering a platform to seamlessly combine the unique properties of both components [2].This convergence opens up new avenues for innovative applications and further reinforces the versatile role of transparent polymer nanocomposites in advancing modern materials and technologies [10].1300 (2024) 012020 IOP Publishing doi:10.1088/1757-899X/1300/1/012020 2 Various studies have investigated the preparation and characterisation of Polymer Nanocomposites (PNCs), employing PMMA as the polymer matrix and integrating metal oxide fillers such as TiO2, SnO, ZnO, CuO, and SiO2 [1], [11], [12].Within the realm of transparent polymer nanocomposites, a research gap exists in exploring the preparation and characterization of PNC films using PMMA and MgO NPs.The inclusion of metal oxide nanoparticles, such as Magnesium Oxide (MgO), enhances the already impressive optical properties of these materials.Among other metal oxide nanomaterials, MgO stands out for its cost-effectiveness and eco-friendly nature, with lower toxicity than alternative metal oxides [13]- [15].
Blending PMMA with MgO nanoparticles introduces distinctive contributions to the optical characteristics of PNC films.This integration not only capitalizes on the inherent advantages of the polymeric component (processability, transparency and flexibility) but also utilises MgO's potential for tailored thermal, electrical, and optical properties.Polymers, known for their economic and technological benefits, especially in automotive, chemical sensors, and electronics, gain further advantages through the strategic integration of MgO nanoparticles.
The study recognizes these composites as particularly appealing for enhancing multifunctional optoelectronic devices and smart, flexible lightweight microelectronics.The synergistic relationship between polymer versatility and MgO's tailored properties positions these materials as promising solutions for those seeking cost-effective and eco-friendly advancements in advanced materials and nanocomposites.Given the mentioned details, this research aims to investigate the comprehensive structural behaviour through XRD data analysis, morphology via AFM, optical properties using UV-Vis spectroscopic measurements, and chemical interactions through FTIR.The focus is on PNC films prepared through a sonicated solution casting method with a PMMA matrix loaded with MgO nanoparticles.

Experimental Details
Polymer films were produced using the solvent casting method, involving the preparation of a poly(methyl methacrylate) (PMMA) stock solution by dissolving 1 gram of PMMA in 15 ml of chloroform.The PMMA solution was stirred until complete dissolution using a magnetic stirrer at room temperature.Simultaneously, magnesium oxide (MgO) nanoparticles were dispersed in chloroform at different weight percentages.The PMMA solution and MgO nanoparticle dispersions were combined and stirred for an hour to achieve proper blending and homogeneity, crucial for uniform distribution within the PMMA matrix.A separate pure PMMA film was prepared for comparative analysis, excluding MgO nanoparticles.The resulting doped nanocomposite and pure PMMA solutions were poured into Petri dishes and allowed to dry, forming MgO-doped PMMA polymer films.These films were systematically labelled based on the incorporated MgO weight percentages.The prepared PMMA-MgO PNC films exhibited a uniform thickness ranging from 0.12 to 0.17 mm and were devoid of air bubbles.
The X-ray diffraction (XRD) analysis of the prepared samples was conducted using a Rigaku Miniflex 600 X-ray powder diffractometer.Fourier-transform infrared spectroscopy (FTIR) spectra were obtained using an Alpha Bruker ATR-FTIR instrument.Surface morphology images were captured utilizing Atomic Force Microscopy (AFM).The optical properties of the films were assessed through UV-Visible microscopy.

XRD
Figure 1(a) showcases the X-ray diffraction pattern of MgO nanoparticles, with peaks aligning well with the typical MgO diffraction pattern [JCPDS No. 87-0652].The grain size was calculated by employing Scherer's formula and it is found to be 22 nm. Figure 1(b) shows the XRD pattern of the PMMA-MgO sample.An amorphous peak at 13° confirms the presence of PMMA polymer in all the samples.Notably, MgO-doped PMMA polymer composite films exhibit robust peaks characteristic of MgO nanoparticles, confirming their integration into the composite (16).The intensity of peaks varies nonlinearly with filler concentration.Furthermore, XRD analysis reveals that the positions of the original peaks of pristine MgO nanofillers remain unchanged upon dispersion in the host PMMA matrix.This indicates that MgO nanofillers maintain their original structure within the PMMA-MgO polymer nanocomposite (12).It's worth noting that no impurity peaks are detected, affirming the purity of the sample (4).

FTIR
FTIR spectroscopy provides valuable insights into the interface affinity between PMMA-MgO.Figure 1(c) presents the FTIR spectra of pure PMMA, MgO nanoparticles and various compositions of PMMA-MgO nanocomposites.Notably, the intensity of transmission spectra demonstrates a linear reduction with an increase in filler concentration, suggesting the presence of MgO in the polymer composite [16].All samples exhibit a consistent pattern of peaks without any deviation.Additionally, PMM2 and PMM4 samples reveal peaks below 400 cm -1 , attributed to the metal oxide Mg-O stretching.The band at 1719 cm -1 is associated with C=O stretching vibrations, while the band within the range of 1140 to 1270 cm -1 corresponds to C-O stretching vibrations.The band at 1067 cm -1 is observed due to -C-O-C stretching vibration.In the spectral range of 1492-1275 cm -1 , additional bands are linked to CH3 bending vibrational modes.Additionally, asymmetric stretching of CH3 vibrations was observed in the range of 2998-2950 cm -1 .The significant decrease in the intensities of the entire FTIR spectra may be attributed to the intermolecular bonding between the PMMA matrix and MgO NPs [17].Thus, FTIR studies provide supporting evidence for the results obtained from XRD. presence of nanoparticles on the surface of the composite film [18].This observation supports the effective dispersion of MgO nanoparticles within the PMMA matrix.

UV-VISIBLE SPECTROSCOPY
The optical absorption spectra analysis provides insights into the band structure and energy band gap of polymeric materials.Figure 3(a) illustrates variations in absorption across incident wavelengths (190-800 nm) for PMMA-MgO samples.In the UV spectrum of nanocomposite samples, absorption notably increases within the 190-250 nm range under UV radiation exposure.The pure PMMA film exhibits minimal absorbance across the visible region (λ = 400-800 nm) but shows increased absorbance in the UV region, confirming its ability to absorb UV radiation [19].UV absorbance features are attributed to electronic transitions within the C=O group of the ester-linked to the repeat unit in the PMMA chain [11].Figure 3(a) indicates that absorption in PMMA-MgO composite films consistently rises with a higher weight percentage of MgO particles integrated into the PMMA matrix, accompanied by a gradual red shift in the sharp absorbance edge.Additional absorbance peaks at 280 nm in doped PMMA samples, increasing with MgO concentration, confirm the presence of MgO nanofiller, supporting XRD results.The plateau in the visible region underscores the transparency of PMMA-MgO composites specifically for photons in this range [19].
The optical transmittance (T%) and reflectance (R%) of PMMA-MgO PNCs are illustrated in Figure 3(b).There was a decline in transmittance in the UV as well as the visible region as the MgO content increased.Within the wavelength range of 240-270nm, there is a sudden decrease in the value of extinction coefficient(k) as shown in Figure 3(d).Beyond 300 nm, k stabilizes at a constant value, suggesting low optical loss in this region [20].Moreover, with an increase in MgO content in the PNCs, k also rises, indicating heightened light dissipation due to scattering and absorption by MgO nanoparticles [21].This significant interaction between the MgO nanoparticles and the polymer blend induces changes in crystallinity, thereby influencing the band structure and absorption percentage [20].
Figure 3(e)presents variation of n, demonstrating a decrease in the refractive index of the films as the wavelength of the incident photon increases, eventually becoming constant at higher wavelengths.The findings further reveal that the refractive index of PMMA-MgO polymer composites rises with increasing MgO content in the visible region.Furthermore, the transparency of the composite samples is underscored by the small values of the extinction coefficient (k) compared to the refractive index (n) [21].The Tauc plot, featured in Figure 3(f), was used to examine the optical properties and distinguish the optical bandgap of the material.The observed linear segment confirms a direct bandgap in PMMA-MgO PNC film.The film's bandgap was established by extrapolating the linear section of the Tauc plots.The band gap of the pristine films slightly decreased from 5.089 eV to 5.069 eV as the filler concentration increased.PNCs characterized by transparency and a high refractive index hold significant potential across various applications in optical design and advanced optoelectronic devices.These applications encompass technologies like LEDs, image sensors, and waveguide systems [22].

Conclusion
This study comprehensively investigates the structural, morphological, and optical characteristics of PMMA-MgO nanocomposite films fabricated via a solution-casting approach.XRD analysis confirms the successful integration of MgO nanoparticles in the PMMA polymer matrix.FTIR spectroscopy reveals intermolecular bonding between PMMA and MgO.AFM studies demonstrate increased surface roughness with higher MgO loading.UV-visible spectroscopy highlights enhanced UV absorption and the presence of a distinctive MgO peak at 280 nm.The refractive index rises with increasing MgO content, while the optical bandgap shows a marginal reduction.The key findings underscore the potential of PMMA-MgO nanocomposites for diverse optoelectronic applications requiring customizable optical properties.The eco-friendly nature and cost-effectiveness of MgO make these nanocomposites economically viable.Overall, this study provides significant insights into the structureproperty relationships in PMMA-MgO nanocomposites.Further tuning the properties through optimal selection of materials and methods can aid the development of these multifunctional nanocomposites for advanced technologies and devices.