Orientational Proliferation and Successive Twinning from Thermoreversible Hexagonal−Body-Centered Cubic Transitions

Abstract

The deterministic proliferation of the orientation of hexagonally packed cylinders (HEX) from the twinned body-centered cubic (BCC) phase is investigated by synchrotron small-angle X-ray scattering (SAXS) and rheo-optical methods for di-and triblock copolymers of styrene and isoprene (SI and SIS). Repeated heating and cooling cycles starting from an initially aligned HEX produce a proliferation of cylinder orientations from successively twinned BCC states. The evolution of the orientation distribution of HEX cylinders produces a decrease in the birefringence and increase in the modulus with each successive generation. The cylinder axes of the degenerate HEX states coincide with the 〈111〉 directions of the twinned BCC due to the epitaxial growth of cylinders from the twinned BCC. The distribution of the cylinder axes of the degenerate HEX states among the 〈111〉 directions of the twinned BCC is found to be affected by memory of the prior HEX state, which decays with annealing time in the BCC state.

Process and kinetics of order–order transition from bcc-sphere to hex-cylinder in polystyrene-block-polyisoprene-block-polystyrene: Time-resolved SAXS and TEM studies

“…1(a); On the other hand, in the OOT from bcc-sphere to hex-cylinder, spheres along the [111] direction of a bcc lattice are deformed and interconnected to cylinders, as also shown in Fig. 1(a) [4,7,26,28]. Here, Fig.…”

“…Since then, the studies about the OOT were advanced not only theoretically [8,9,[18][19][20][21][22][23][24][25] but also experimentally. Especially, the OOT between hex-cylinder and bcc-sphere were most studied, [2,[4][5][6][7][26][27][28] and as a consequence, the OOT process was elucidated as follows: In the OOT process from hex-cylinder to bcc-sphere, the cylinders are burst into a series of spheres with the cylindrical axes being transformed to the [111] direction of bcc-sphere as schematically shown in Fig. 1(a); On the other hand, in the OOT from bcc-sphere to hex-cylinder, spheres along the [111] direction of a bcc lattice are deformed and interconnected to cylinders, as also shown in Fig.…”

Self-assembled block copolymers: Bulk to thin film

“…63 These microdomains except CPS have been verified experimentally for many different block copolymers, as shown in Figure 1 (b). [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] On the other hand, the CPS phase (either face-centered cubic spheres or hexagonally packed cubic spheres), which is located between disordered state and Im3m, has not been found for neat diblock copolymer. However, the CPS phase was found for a diblock/solvent mixture [56][57][58][59] and diblock/ homopolymer mixture system.…”

Crystal symmetry and the reversibility of martensitic transformations

“…Similar observations were made in FeMnCrSiNi steels 18,19 . Finally, in a block co-polymer, the (reconstructive) bcc-to-hexagonal transformation was observed to be irreversible because of orientation proliferation through twinning in both phases 20 .…”

“…The idea is that a partially transformed region causes stress and plastic deformation. However, a system like the styrene block co-polymer considered by Lee et al 20 should largely be unaffected by any volume change. Our explanation is independent of such a volume effect.…”