Stacking and Colloidal Stability of CdSe Nanoplatelets

Abstract

Colloidal CdSe nanoplatelets with\nmonolayer control over their\nthickness can now be synthesized in solution and display interesting\noptical properties. From a fundamental point of view, the self-assembly\nof CdSe nanoplatelets can impact their optical properties through\nshort-range interactions, and achieving control over their dispersion\nstate in solution is of major relevance. The related issue of colloidal\nstability is important from an applicative standpoint in the perspective\nof the processing of these materials. Using UV–vis spectroscopy,\nwe assess the colloidal stability of dispersions of CdSe nanoplatelets\nat different nanoparticle and ligand (oleic acid) concentrations.\nWe unravel an optimum in oleic acid concentration for colloidal stability\nand show that even moderately concentrated dispersions flocculate\non a time scale ranging from minutes to hours. Small-angle X-ray scattering\nshows that the precipitation proceeds through a face-to-face stacking\nof the nanoplatelets due to long-ranged van der Waals attraction.\nTo address this issue, we coated the platelets with a carboxylic acid-terminated\npolystyrene, thus achieving colloidal stability while retaining the\noptical properties of the platelets.