SIZE CONTROL OF NANOPARTICLES IN SEMICONDUCTOR-POLYMER COMPOSITES .1. CONTROL VIA MULTIPLET AGGREGATION NUMBERS IN STYRENE-BASED RANDOM IONOMERS

A priori knowledge of ionic aggregate sizes in random ionomers has been applied to the synthesis of semiconductor nanoparticles of predictable sizes. The size control of quantum-confined cadmium sulfide (CdS) and lead sulfide (PbS) clusters in the range of 2R = 18-23 Angstrom was accomplished within styrene-based random ionomers with ionic groups located at the ends of side-chains of variable lengths. CdS and PbS clusters were precipitated within the ionic aggregates (multiplets) of the ionomer, to form composites of semiconductor nanoparticles dispersed in a polymer matrix. The sizes of the semiconductor clusters increased with increasing side-chain length, and an approximate linear relationship was shown between the cluster sizes and the lengths of the side chains. These results are in agreement with the previous finding that the size of the ionic multiplet increases with the length of the side chain and show that a knowledge of ionic aggregate sizes can be used to form nanoparticles of predictable sizes. The semiconductor-polymer composites were characterized by UV-vis spectroscopy, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). This is the first of two papers in which the size control of semiconductor clusters through the primary ionic aggregate sizes of various ionomers is demonstrated. In the next paper, the use of PS-b-PACd diblock ionomers to precipitate CdS clusters of predictable sizes in the range 2R = 29-50 Angstrom will be described.