Article ID Journal Published Year Pages File Type
5187135 Polymer 2006 14 Pages PDF
Abstract

We have conducted the systematical investigations for the ordering process and kinetics of both hexagonally packed cylindrical microdomains (hex-cylinder) and spheres in a body-centered cubic lattice (bcc-sphere) from spherical microdomains with a short-range liquid-like order (disorder-sphere) over a wide range of quench depth for a polystyrene-block-polyisoprene-block-polystyrene triblock copolymer, having order-order transition (OOT) temperature, TOOT, at 190 °C between hex-cylinder and bcc-sphere, by using time-resolved small-angle X-ray scattering. As a result, we clearly assessed a range of temperature over which the two-step ordering from disorder-sphere to hex-cylinder occurs. A possible interpretation for the two-step ordering process was proposed in the text. The following three kinds of ordering processes are observed. (i) The single-step ordering of hex-cylinder: when the system is quenched into the temperature below 183.2 °C, hex-cylinder is directly transformed from disorder-sphere via the nucleation and growth process. The incubation time for the nucleation and the transition rate largely depend on the quench depth. (ii) The ordering of bcc-sphere: when the system is quenched into the temperature above 190 °C in the bcc-sphere phase, bcc-sphere is formed from disorder-sphere via the nucleation and growth process. The quench-depth dependence of the incubation time is very small, compared with that for hex-cylinder, and the transition rate is independent of the quench depth. (iii) The two-step ordering of hex-cylinder: when the system is quenched into the temperature range from 183.2 to 190 °C, the volume-filling metastable bcc-sphere is first developed by nucleation and growth, followed by the OOT from metastable bcc-sphere to hex-cylinder via the nucleation and growth process. The incubation time for the formation of metastable bcc-sphere is very close to that for the formation of equilibrium bcc-sphere, and the transition rate for the formation of metastable bcc-sphere is independent of the quench depth. Thus, the ordering pathways for the volume-filling of metastable bcc-sphere are almost identical to that for the volume-filling equilibrium bcc-sphere. The incubation time for the OOT from metastable bcc-sphere to hex-cylinder is longer than that for the formation of metastable bcc-sphere, and the transition rate for the former is also slower than that for the latter. Moreover, the incubation time for the OOT from metastable bcc-sphere to hex-cylinder is longer than that for that from equilibrium bcc-sphere to hex-cylinder, and the transition rate for the former is also slower than that for the latter, because metastable bcc-sphere is considered to be more distorted than the equilibrium bcc-sphere, which suppress the epitaxial growth of hex-cylinder along a [111] direction of bcc-sphere.

Related Topics
Physical Sciences and Engineering Chemistry Organic Chemistry
Authors
, , , ,