Supercritical Fluid Assisted Dispersion of Nano-Silica Encapsulated CdS/ZnS Quantum Dots in Poly(ethylene-co-vinyl acetate) for Solar Harvesting Films

Transparent polymer/inorganic nanocomposites are of great interest for solar harvesting films with quantum dots (QDs) which provide light tuning to the existing polymeric material. However, achieving a high level of QD dispersion without compromising the optical, thermal, and mechanical properties has been a key challenge. In this work, we explore a novel supercritical carbon dioxide (scCO(2)) synthesis method that utilizes scCO(2) to enhance the homogeneous dispersion of encapsulated and functionalized QDs into ethylene vinyl acetate (EVA) copolymer. The core/shell CdS/ZnS QDs were first encapsulated with silica to improve their photoluminescence and stability. The silica surface of the QDs then vinyl functionalized by the addition of vinyltrimethoxysilane (before or during polymerization). QDs dispersion in the EVA polymer network was characterized by SEM, TEM, and CLSM. The results demonstrated that scCO(2) improved the dispersion of QDs within the polymer matrix with uniform dispersion being observed for a two-step process (functionalization before polymerization). FTIR confirmed the successful functionalization on the silica surface. The vinyl acetate content of the EVA copolymer and nanocomposite was 33.5% calculated using the TGA. The optical study results show that with a very low loading of QDs (similar to 1%) up to 80% UV bleaching was prevented while retaining more than 90% visible light transmission. The experimental nanocomposite films also showed improved thermal and mechanical properties, showing the utility of this approach for next-generation solar harvesting films.