The Modification Of QDs With POSS And Preparation Of PVB/QDs@POSS Composites

Quantum dots (QDs) are of great interest for various prospective applications in light-emitting diodes, solar cells, sensors, biological fluorescence labeling and imaging.due to their unique size-dependent optical properties. However, QDs exist in the form of colloid solution or powder, which limits their practical applications. To realize the transformation from nanomaterial to devices, QDs need to be incorporated into other matrices to improve the stability and processbility. Because of their stable physicochemical properties, facile processability and low cost, organic polymers are often used as matrices for these novel QDs. Therefore, QDs/polymer composites have received much attention.In this paper, several polyhedral oligomeric silsesquioxane (POSS) were used to modify CdSe/CdS/ZnS core-shell QDs and then transparent PVB/QDs composites were prepared by solution blending method. The structure and photoluminescence of POSS modified QDs and their corresponding composites were studied in detail by fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), atomic force microscope (AFM), UV-visible absorbance spectroscopy (UV) and photoluminescence spectra (PL).First of all, QDs with two different emitting wavelengths were modified by mercaptopropylisobutyl POSS (POSS-SH) based on the thiol-metal affinity interactions. The results show that the fluorescence intensity increases slightly after the modification of QDs, which is attributed to the elongation of light path inside the gain media and the reduction of surface defects. The as-prepared PVB/QDs@POSS-SH films emit bright and homogeneous light under UV excitation (λ=365nm). Surface morphology analysis demonstrates that POSS-SH can improve the compatibility of QDs with PVB effectively, resulting in well dispersion of QDs in PVB.Secondly, self-assembly of QDs was achieved via electrostatic force between negatively charged mercaptopropionic acid (MPA) capped QDs and positively charged octa(3-ammoniumpropyl)octasilsesquioxane octachloride (OA-POSS), which was subsequently introduced into PVB matrix. The results show that QDs aggregates are formed, generating collective properties that are not found in the individual components, leading to the enhanced fluorescence intensity. The as-prepared film with outstanding optical properties is very smooth and flat. Surface morphology analysis indicates that QDs aggregates are well dispersed in PVB matrix.Finally, QDs were self-assembled based on electrostatic interaction between positively charged polyethyleneimine (PEI) coated QDs and octa(tetramethylammonium)-polyhedral oligomeric silsesquioxane (TMA-POSS) with negative charge, which were then incorprated into PVB matrix. The results show that the fluorescence intensity of QDs is enhanced through the modification of TMA-POSS. The surface of as-prepared film is very smooth and flat, exhibiting excellent optical properties. Moreover, QDs aggregates are compatible with PVB, which is in agreement with well dispersion of QDs in PVB.