Order–Order Transition between Equilibrium Ordered Bicontinuous Nanostructures of Double Diamond and Double Gyroid in Stereoregular Block Copolymer

Abstract

While ordered bicontinuous double diamond (OBDD) in block copolymers has always been considered as an unstable structure relative to ordered bicontinuous double gyroid (OBDG), here we report the existence of a thermodynamically stable OBDD structure in a diblock copolymer composed of a stereoregular block. A slightly asymmetric syndiotactic polypropylene-block-polystyrene (sPP-b-PS) as cast from xylene was found to display the OBDD morphology. When the OBDD-forming diblock was heated, this structure transformed to the OBDG phase at ca. 155 °C. Interestingly, OBDD was recovered upon cooling even in the temperature range above melting point of sPP, indicating that OBDD was a thermodynamically stable structure for sPP-b-PS melt, which was in contradiction to the conventional view. We propose that the larger free energy cost encountered in OBDD due to the larger packing frustration may be compensated sufficiently by the release of free energy due to local packing of the conformationally ordered segments of sPP blocks, which stabilizes the OBDD structure at the lower temperatures.

Formation of Single Gyroid Nanostructure by Order–Order Phase Transition Path in ABC Triblock Terpolymers

“…Serious packing frustration remains an obstacle for stabilizing the complex network structures. [15c,d,29a,37] To accomplish the stabilizing of complex ordered phases, various strategies have been developed. Blending of the designed polymers (homopolymers or block copolymers) has proven to be an effective route to fabricate complex spherical packing phases (such as the Frank–Kasper phases), kaleidoscopic tiling patterns, as well as multiply continuous networks.…”

“…First, in contrast to DG and G A phases, SG phase, as yet, has never been demonstrated to be stable in pure block copolymer system. Exploiting various strategies to mitigate packing frustration, including the addition of conformationally ordered segments and appropriate homopolymers, can stabilize certain metastable double and alternating networks, such as DD and even the P phase. [15e,16] Unfortunately, this strategy does not prove effective for the SG.…”

“…Exploiting various strategies to mitigate packing frustration, including the addition of conformationally ordered segments and appropriate homopolymers, can stabilize certain metastable double and alternating networks, such as DD and even the P phase. [15e,16] Unfortunately, this strategy does not prove effective for the SG. Second, the addition of inorganic nanoparticles may result in a robust framework, as shown in the various fabrication routes for the SG mentioned above, along with those for numerous surfactant‐directed mesoporous crystals .…”

Thermal Approaches to Perpendicular Block Copolymer Microdomains in Thin Films: A Review and Appraisal

“…Under the appropriate annealing conditions, BCPs can self‐assemble into periodic nanostructures whose grain size may span up to arbitrarily large sizes. The formation of classical (lamellae, hexagonally close packed cylinders, spheres, and double gyroids) and non‐classical (ordered bicontinuous double diamond, Fddd , and Frank–Kasper σ phase) morphologies of said nanostructures are primarily dependent on the relative volume fraction of the two blocks, and their lattice spacing primarily dependent on the total molecular weight of the BCP.…”

The Formation of OTDD Network Structure in PS‐b‐PI‐b‐PDMS Triblock Terpolymer

“…It should be noticed that the OBDD (ordered bicontinuous double diamond) and OTDD have been considered as unstable structures, and the OTDD in this study is not stable, either. However, recently OBDD has been reported as a thermodynamically stable structure in a sPP‐ b ‐PS diblock copolymer, since the thermoreversible transition between OBDD and gyroid has been confirmed …”