(319f) Surface Engineered Quantum Dots for Light Selective Polymer Films

We have investigated the optimization of the optical properties of polymer films integrating engineered quantum dot (QD) nanocrystals to manipulate and control light transmission for applications in light selective polymer films. Highly luminescent CdS QDs and CdS/ZnS core/shell QDs with 5 nm size were synthesized using a facile approach based on the pyrolysis of single molecule precursors. After capping the CdS QDs with a thin layer of ZnS to reduce toxicity, the photoluminescence and photostability of the core-shell QDs was significantly enhanced. The ZnS shell was found to passivate the surface defects of the CdS dots while confining the electron-hole pair to the CdS core region.

To make both the bare and core/shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interaction and surface silanization. Mesoporous silica can protect completely both type of QDs from photobleaching and also improves the quantum yield by providing much stronger resistance to oxidation and Oswald ripening of QDs. The encapsulated QDs were then functionalized using silane coupling agent and integrated to poly ethylene vinyl acetate (pEVA) network both by melt mixing (using twin screw extruder) and grafting from polymerization in supercritical CO₂. Morphology, UV absorption, visible light transmission, and IR retention were observed and compared to that obtained from commercial pEVA greenhouse plastics. Mesoporous silica encapsulated QDs into EVA polymer films were found to provide simultaneous UV protection, infrared retention, and light selectivity of solar-polymer films.