| 초록 |
The phase behavior of a symmetric styrene-isoprene (SI) diblock copolymer in a styrene-selective solvent was investigated by in-situ small angle X-ray scattering on shear-oriented solutions. A remarkable new feature in this phase diagram is the peculiar coexistence of both bcc and hcp phases between cp and hex in the concentration range of Φ = 0.33 ~ 0.45. Accordingly, in present study, this aspect of the phase behavior, in particular, the kinetics among the cp, bcc/hcp mixture, and hex phases was investigated in detail. By focusing on the transition relationship among these various ordered phases in terms of heating and cooling, we observed hysterisis between heating scan and cooling scan, namely, super-cooled cylinders were formed by cooling scan. The stability of these super-cooled cylinders is quite dependent on concentration and for Φ > 0.40, the super-cooled cylinders do not go back to spheres even the annealing time for one month. This is to say that by increasing the polymer concentration, the spontaneous formation of spheres due to the dissociation of cylinders is kinetically not favored since the hex phase are large in size as well as in number and are not amenable to any pre-transitional fluctuation of cylinders prior to the cylinder-to-sphere transition. A schematic illustrating the region of long-lived cylinder domains as a function of concentration of block copolymer solution is finally given and this transition kinetics between spheres and cylinders are confirmed by a combination of rheology and static birefringence. |
