The effects of the selectivity of the toluene/ethanol mixture on the micellar and the ordered structures of an asymmetric poly(styrene-b-4-vinylpyridine)

The effects of the solvent selectivity of toluene/ethanol mixtures on the micellar and ordered structures of an asymmetric diblock copolymer of PS(19.6 K)-b-P4VP(5.1 K) in the dilute (1 wt%) and semi-dilute (8 wt%) solutions, as well as in the gel and solid films, were studied using small angle X-ray scattering (SAXS), generalized indirect Fourier transform (GIFT), and transmission electron microscopy (TEM) methods. The solvent selectivity was controlled by ϕ (weight percentage of ethanol in toluene/ethanol mixture). Individual micelles, space-filled micellar structure (without three-dimensional order), and three-dimensionally ordered gel and solid structures were observed from the 1 and 8 wt% solutions, the gel, and the solid film, respectively. In the 1 wt% solution, the individual micellar structures were strongly dependent on ϕ; the spherical micelles with P4VP core at ϕ = 0, the unimer state at 10 ≤ ϕ ≤ 50, the spherical micelles with PS core at ϕ = 60, the cylindrical micelles with PS core at ϕ = 70 and 80, and precipitation at ϕ = 90 and 100 were observed. The 8 wt% solution was close to overlap concentration with the unimer state in the regions of 20 ≤ ϕ ≤ 40. In the gel, the ordered structure was observed in the sequence of bcc, hexagonal, gyroid, lamellar, reverse hexagonal and random as ϕ increased, and could be explained by the change of the relative volume fraction of each block as ϕ changed, similar to the phase sequence in the phase diagram of the diblock copolymer. The solid films showed the various kinetically frozen ordered microstructures such as randomly packed sphere, hexagonal, gyroid, hexagonally perforated lamella, reversed hexagonal, and randomly packed cylinder, which were controlled by the solvent quality in the gel before solidification. We believe that these results can be applied to photonic crystals, self-assembled nano-patterning, and functional nanoparticles in which the structural control is most important.