Transitions of domain ordering and domain size in a spherical-forming polystyrene-block-poly(ethylene oxide) copolymer and its composites with colloidal cadmium sulfide quantum dots

With specific annealing schemes applied to a neat polystyrene-block- poly(ethylene oxide) (SE) and its composites with cadmium sulfide quantum dots (CdS QD), we have observed microdomain structures and phase transitions in the system using temperature-resolved small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Both TEM images and SAXS results show clearly that incorporation of surfactant-tethered CdS QD preferentially into PEO blocks leads to increases in thermal stabilities of both bcc-packed lattice (referred as long-range order) and microdomains themselves in the sphere-forming SE/CdS composites. The bcc-packed lattice in the SE/CdS composites sustains better than that in the neat SE, during a temperature elevation to ∼160 °C, at which the bcc-packed SE/CdS spheres start to transform into micelles with a short-range liquid-like order. Quantitative model analysis shows that the PEO/CdS micelles can retain their size in the SE/CdS composites up to 200 °C, whereas the PEO micelles shrink after the softening of the PS matrix around 100 °C, and disassociate largely into the PS matrix of the neat SE at 160 °C.