A study on the selectivity of toluene/ethanol mixtures on the micellar and ordered structures of poly(styrene-b-4-vinylpyridine) using small-angle X-ray scattering, generalized indirect Fourier transform, and transmission electron microscopy

The effects of the selectivity of toluene/ethanol mixtures on the micellar and ordered structures of PS(12K)-b-P4VP(11.8K) in the dilute, semidilute, and concentrate solutions, as well as in the solid state, were studied using small-angle X-ray scattering (SAXS), generalized indirect Fourier transform (GIFT), and transmission electron microscopy (TEM) methods. For the dilute solutions (1 wt %), only form factors were observed in SAXS at phi (weight percent of ethanol in the ethanol/toluene mixture) = 0 to 20 and 70 to 100 (selective solvents), while isotropic states were found at other solvent mixture ratios (nonselective solvents). Hard and large spherical micelles were formed in high-selective solvent mixtures while soft and small ones were formed in less-selective solvent mixtures. For the semidilute solution (8 wt %), both of structure and form factors of SAXS curves appeared in selective solvents while isotropic states were also observed in nonselective solvents. The form factors that were separated by using GIFT were similar to those from the dilute solution. For the concentrated solution (16 wt %), new soft micelles, which were in an isotropic state in the dilute and semidilute solutions, were formed in nonselective solvents by increasing the concentration of the solution to 16 wt %. The cubic packing of spherical micelles could be observed in entire solvent mixtures, except for the solution at phi = 40, which had two-dimensional hexagonal packing. Hard micelles favored a fcc symmetry, although soft micelles favored a bcc symmetry. During drying from the 16 wt % solution to a solid state, hard spherical micelles remained and were randomly packed although soft micelles were transformed into thermodynamically stable lamellar structures. The hexagonally packed structures at phi = 40 maintained their original hexagonal packing after drying. The various structures for PS(12K)-b-P4VP(11.8K), such as hard/soft spherical micelles in the dilute solution, fcc, bcc, and hexagonal packing in the concentrate solution, and randomly packed micellar, lamellar, and hexagonal structures in the solid state, could be finely tuned by using a simple toluene/ethanol mixture in this study.