Directed Self-Assembly of Block Copolymers into Twin BCC-Sphere: Phase Transition Process from Aligned Hex-Cylinder to BCC-Sphere Induced by a Temperature Jump between the Two Equilibrium Phases

Abstract

We explored in situ a "directed" self-assembly of block copolymers into a twinned body-centered cubic sphere (bcc-sphere) with a special orientation via the order−order phase transition from a specially aligned hexagonal cylinder (hex-cyl) by using time-resolved synchrotron small-angle X-ray scattering and transmission electron microscopy. We elucidated that the hex-cyl with its cylinder axis and {11} lattice plane aligned respectively parallel to the OX axis and the OXZ plane was epitaxially transformed into the twin bcc-sphere with its twin axis ⟨111⟩ and twin plane {112} having respectively the "directed orientation" parallel to the OX axis and the OXZ plane. We found that the directed self-assembly involves a three-step nucleation growth (NG) process as follows.Step I corresponds to a pretransition process, where hex-cyl undergoes the cooperative and periodic undulation of the cylinders with their pinching or bulging points being spatially arranged with the "bcc symmetry" which is attained in bcc-sphere after completion of the transformation (designated as "undulated hex-cyl"). Moreover, the undulation fluctuations modes found to have the degeneracy in the form of the undulations with bcc-symmetry A and those with bccsymmetry A′ which have the twin relationship to each other.Step II involves NG of two types of bcc-sphere (designated as Aand A′-sphere which have a mirror symmetry with respect to the {112} plane parallel to the OXZ plane) formed with an equal statistical weight in the matrix of the undulated hex-cylinder; Grains of bcc-sphere grow at the expense of the matrix phase at a faster growth rate parallel to ⟨111⟩ axis than normal to it. Step III involves impingements of bcc-sphere A and A′ with their twin planes {112} as their grain boundaries and with their twin axes ⟨111⟩ parallel to the OXZ plane and the OX axis, respectively. Thus, the volume-filling A-and A′-spheres accompanied by spatial rearrangements toward a more perfect bcc-sphere are inevitably directed to form twin bcc-sphere composed of bcc-sphere A and A′.

Phase diagrams of block copolymer melts by dissipative particle dynamics simulations

“…Whereas cylinders are almost as well studied as lamellas, the S microstructure in copolymers is rather common only in experimental systems, where it can be obtained either by orderdisorder transition (ODT) 56 or order-order transition (OOT). 57 Its identification by SCFT, 13 in Monte Carlo 19,20 and even DPD 25,41 simulations is usually difficult, if not impossible because of the long equilibration time. Figure 5 reports on the least ordered structures with illdefined peaks on the S(q) dependence.…”

Extraordinary boundary morphologies of large-scale ordered domains of spheres in thin films of a narrowly dispersed diblock copolymer via thermodynamic control

“…For block copolymers with bulk BCC structures, many theoretical and experimental studies have been focused on the order-order and order-disorder transitions induced by the substrate and confinement in thin films. 14,[19][20][21][22][23][24] Moreover, ordering of the spheres along the direction normal to the substrate in thin films of asymmetric diblock copolymers with relatively larger layer thicknesses was reported, 25 while the spheres were almost short-range ordered in the plane parallel to the substrate. 26 However, the lateral order and ordering range of the BCC spheres as well as the morphologies at the boundaries of the adjacent ordered domains in thin films of asymmetrical BCP with a thickness within a certain range are rarely investigated.…”

Melt-mixed nanocomposites of SIS/MWCNT: rheological, electrical and structural behavior

“…It is known that the stability of different equilibrium domain morphologies of a block copolymer depends on the relationship between enthalpy (interaction energies between dissimilar polymer blocks given by the Flory-Huggins interaction parameter, χ) and entropy (conformational energy χ and f, the volumetric fraction of one of the co-monomers. Numerous studies have showed various types of equilibrium morphologies of di-blocks AB and tri-blocks ABA copolymers, which are spheres (S), cylinders (C), lamellas (L) and gyroids (G) [45][46][47] . When f is near 0.5, lamellar morphologies are usually expected after annealing during several days.…”