Optimizing Optical Properties of Poly(methylmethacrylate)-Zirconia Nanocomposites

Transparent nanocomposites are a promising class of functional materials with potential applications in eyeglass lenses, optical coatings, and display technologies. In this work, we present an approach to fabricating Poly(methyl methacrylate) (PMMA)-based nanocomposites by incorporating crystalline and monodisperse zirconium dioxide (ZrO2) nanoparticles of just a few nanometers in size. This is achieved through a processing method that utilizes fully polymerized PMMA, following an ex-situ approach. In contrast to in-situ techniques, which involve mixing nanoparticles with the monomer to achieve high homogeneity and uniform distribution, ex-situ processing allows for better scalability and enables the reuse of pre-synthesized polymers by dissolving them in suitable solvents. ZrO2 was selected as the filler material due to its chemical stability and inertness, avoiding issues like photochemical degradation of the PMMA matrix observed with TiO2. To facilitate the dispersion of ZrO2 in apolar solvents, the nanoparticles were functionalized with a carboxylic acid, which also acted as a plasticizer for PMMA, enhancing ductility and reducing brittleness. Common challenges of ex-situ techniques include air inclusions during the initial drying step and inhomogeneities caused by particle aggregation or uneven distribution of particles within the composite, were addressed through a streamlined freeze-milling, drying, and hot-pressing process. This approach led to a remarkable enhancement in the lighttransmittance of the composite, demonstrating its effectiveness in overcoming some of the most pressing issues in the ex-situ preparation of nanocomposites. To further understand the relationship between the nanocomposite’s structure and its optical properties, advanced theoretical models such as Maxwell-Garnett Modell and Mie scattering theory are applied to calculate the effective refractive index and light scattering behaviour of the nanocomposite. Experimental analysis using X-Ray Powder Diffraction (XRPD) and Rietveld Refinement revealed that the ZrO2 nanoparticles comprised a mixture of monoclinic and cubic/tetragonal phases, providing essential structural insights for accurate optical modelling. This study demonstrates the potential of ex-situ processing to overcome traditional limitations in nanocomposite fabrication, providing a scalable and sustainable route to produce optically enhanced materials and paving the way for advanced applications in optics and beyond.