Single Helix to Double Gyroid in Chiral Block Copolymers

Abstract

An order−order phase transition of chiral block copolymers (BCPs*) from single helix to double gyroid (H* → G) through a nucleation and growth process was demonstrated. The H* and G phases can be obtained by solution casting from fast and slow solvent evaporation, respectively, suggesting that the H* phase is a metastable phase. Consequently, the coexistence of H* and G phases can be found in the solution-cast samples from intermediate solvent evaporation. To truly examine the transition mechanism of the H* → G, electron tomography was carried out to directly visualize the morphological evolution in real space, in particular, the transition zone at interface. Unlike the mechanisms for the transitions of block copolymers (BCPs) by considering the interdomain spacing matching, a significant mismatch in the lattices for the H* → G was found. Consequently, the transition may require an adjustment on the geometric dimensions to justify corresponding lattice mismatch. As a result, the morphological observations from electron tomography offer new insights into BCP phase transitions.

Hierarchical Self‐Assembly in Liquid‐Crystalline Block Copolymers Enabled by Chirality Transfer

“…CD spectra of long‐time‐annealed films of LCBC‐LTA30 and LCBC‐DTA30 were almost the same, just as what was observed in the PM11AZ 40 ‐TA composites (Supporting Information, Figure S3 a,b). These are quite different from previous work carried out by other groups, which has revealed that molecular chirality usually depended on the enantiopurity of chiral centers, and the chirality induced by left‐handed information should exhibit the reverse CD signals with that induced by right‐handed information . Therefore, the bisignate Cotton CD bands were not induced by the molecular chirality, but rather the aggregate chirality.…”

3D TEM Tomography of Templated Bilayer Films of Block Copolymers

“…Self‐consistent field theory (SCFT) has been used extensively to model the behavior of BCPs, and has been compared with transmission electron microscopy (TEM) or scanning electron microscopy (SEM) images for thin films and for BCPs confined in cylindrical or spherical pores . 3D TEM tomography has been applied to image microdomains in a range of bulk BCPs and even to study the effects of confinement, solvent evaporation rate and nanoparticle incorporation . However, real‐space tomography measurements of BCP morphologies formed by directed self‐assembly, where the templating structures and substrate are still intact, and the images are of sufficient quality to enable model validation, have not previously been carried out.…”

Shifting Networks to Achieve Subgroup Symmetry Properties

“…Here, we suggest a simple method for the preparation of new optical properties of a nanomaterial by network shifting to break the inversion symmetry between the two coherent networks in the DG structure, leading to a nanomaterial with changed optical properties. Inorganic networks in a polymer matrix are fabricated using hydrolyzed DG‐forming PS‐PLLA as a template for sol‐gel reaction, giving robust inorganic frameworks for physical reallocation. The bi‐continuous inorganic networks embedded in the polymer matrix are rearranged by thermal treatment at a temperature above the glass transition temperature (Tg) of the PS matrix.…”