Controlling the Spatial Organization of Oxide Nanoparticles in Polymeric and Ceramic Thin Films

It is important to develop methods to control the spatial distribution of oxide nanoparticles within both polymeric and ceramic thin films. In the synthesis of oxide nanoparticles they are often stabilized by capping ligands such as oleic acid that render them soluble in non-polar solvents such as hexane. When dispersed into a polymer film, however, the stabilized nanoparticles can aggregate due to unfavorable interactions between the oleic acid shell and the polymer matrix. More stable and uniform dispersions can be made by exchanging the original capping ligands with short polymeric ligands identical in composition to the polymer matrix of interest. Preofessor Jeffrey T. Koberstein and Chemical Engineering graduate student Chun-Kwei (Alex) Wu have illustrated this concept. Fe₂O₃ nanoparticles, synthesized by their MRSEC collaborator, Professor Stephen O?Brien, were successfully dispersed in a matrix of poly(dimethyl siloxane) (PDMS) by exchanging the oleic acid ligands with short PDMS chains functionalized with a carboxylic acid group on one chain end. The interparticle spacing can be controlled by changing the molecular weight of the PDMS ligand. The three different molecular weights of PDMS-COOH employed (Mn=1k, 5k, 10k) provide for controlled interparticle spacings as illustrated by the TEM images below (scale bar: 100 nm). The PDMS component of films is subsequently converted to silicon oxide by a mild room temperature UV-ozone treatment to produce Fe₂O₃ nanoparticles suspended in a silicon oxide matrix. Such nanocomposite films are being studied as potential gas separation membranes.


Posted on May 11, 2005.


Transmission electron micrographs of these films, for different molecular weight ligands.