Determination of volume fractions and ligand layer thickness of polymer/CdSe quantum dot blend films by effective medium approximations

We investigate hybrid organic/inorganic films using different polymers and CdSe quantum dots (QD) and nanorods (NR) with hexanoic acid (HA)-treated hexadecylamine (HDA) or pyridine as the capping ligands. The volume ratios of the polymer:nanoparticle (NP) blends are studied by spectroscopic ellipsometry and transmission intensity data. Effective medium approximation based on the results of the pristine films is applied. With this routine, the polymer/NP volume ratio of the blend can be identified. In combination with the mass ratio of the components, the mass density of the NP including the inorganic crystalline core and the organic ligand layer is obtained. A geometrical model for QD and NR allows for the estimation of the ligand layer thickness. We find pyridine and HDA after HA treatment to be 0.9 and 0.6 nm on the QD surface, respectively. By contrast, the effective thickness of the organic ligand is 3.0 nm on the investigated NR. In both cases, the organic layer is thicker than a monolayer of the expected pyridine due to the presence of extant synthesis ligands as a result of incomplete ligand exchange. (C)2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000000, 2011