Spherical Assemblies of Semiconductor Nanoparticles in Water-Soluble Block Copolymer Aggregates

Novel spherical assemblies of CdS-containing block copolymer reverse micelles in aqueous solution have been formed by the slow addition of water to mixtures of the reverse micelles and a polystyrene- b -poly(acrylic acid) stabilizer. The structures are large compound micelles (LCMs) with quantum-confined CdS nanoparticles dispersed throughout a spherical PS matrix, which is stabilized in water by a layer of solubilized hydrophilic chains. The size of the CdS particles (2 R CdS ∼ 3 nm) is controlled by the ionic block length, N B, of the block copolymer making up the reverse micelle. LCM formation is found to be dependent on the amount of added stabilizing copolymer. When the weight of stabilizer relative to the total polymer weight is 12% for the specific system under study, a single population of LCMs is formed ( D ave = 64 nm); each of these LCMs consists of an average of 58 reverse micelles and 87 stabilizing chains, with an average surface area per stabilizing chain of 148 nm. 2 At 10% stabilizer, two LCM populations, D ave = 52 nm and D ave = 152 nm, are formed. When the concentration of stabilizing copolymer is increased to 21 and 35%, regular micelles with no internal structure coexist with LCMs. Without added stabilizing copolymer, most reverse micelles undergo macroscopic precipitation upon water addition, although some LCMs are observed in the remaining solution.