Binding effect of surface-modified cadmium sulfide on the microstructure of PS-b-PEO block copolymers

CdS nanoparticles with surfaces modified by mercaptoethanol have been synthesized for greater solubility in dimethylformamide (DMF) and the ability to preferentially bind to the poly(ethylene oxide) (PEO) blocks of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymer. The size of the surface-modified CdS nanoparticles (M-CdS) in DMF can be characterized by the Schultz distribution of a mean radius of 18.4 Angstrom and a polydispersity of 0.5, using small-angle X-ray scattering (SAXS). These M-CdS nanoparticles can further disperse in the PS-b-PEO, with a slightly larger mean radius than that observed in DMF. The uptake of M-CdS nanoparticles for the PEO blocks of the PS-b-PEO saturates around 7% in volume fraction. The binding of the nanoparticles promotes a segregation of the PEO/nanoparticles and leads to spherical PEO/M-CdS microdomains in the composite film with a greatly enhanced thermal stability. The structural information obtained from X-ray scattering agrees well with the transmission electron microscopy images and differential scanning calorimetry results.