Structural Requirements of Block Copolymers for Self-Assembly into Inverse Bicontinuous Cubic Mesophases in Solution

Abstract

Inverse bicontinuous cubic (IBC) structures consisting of triply periodic minimal surfaces of block copolymers (BCPs) are emerging as materials of interest owing to their structural characteristics, which resemble those of their biological counterparts constructed from lipids. Solution self-assembly of amphiphilic BCPs with nonlinear architectures has recently been shown to form colloidal particles (polymer cubosomes) and macroscopic monoliths having mesoporous networks of water channels embedded in the periodic minimal surfaces of the BCP bilayers. Here we report that BCP architectures play a crucial role in controlling the packing parameter (P) of BCPs; a value greater than unity is a prerequisite for preferential self-assembly into IBC mesophases in solution. We show that the branched architecture of the polymer blocks constituting the BCP critically influences the structural parameters, such as the molecular area and, in particular, the critical length of the hydrophobic domain. Adjusting these structural parameters not only increases the P value of the BCP without depending on the asymmetry of the volume ratio of two polymer blocks (block ratio) but also dictates the lattice and periodicity of the resulting minimal surfaces of the BCPs. Our results could provide a rationale to design and synthesize amphiphilic block copolymers to directly self-assemble into periodic porous structures in solution, which could be promising materials having highly ordered mesopore networks.

Dendrimersomes Exhibit Lamellar-to-Sponge Phase Transitions

“…48 Such control has been possible in analogous block copolymer systems by tuning characteristics such as the branch architecture, polymer length, and block copolymer ratio, suggesting that it would be possible to create a library of DMSs with distinct morphologies and thermally inducible transitions. 17,49,50 …”

Head–Tail Asymmetry as the Determining Factor in the Formation of Polymer Cubosomes or Hexasomes in a Rod–Coil Amphiphilic Block Copolymer

“…Linear PEO‐ b ‐PS can self‐assemble into polymer cubosomes and hexasomes with the volume fraction of PS (and thus the corresponding head–tail asymmetry) increased . For dendritic PEO‐ b ‐dendritic PS, the ABCP can self‐assemble into polymer cubosomes and hexasomes in a lower volume fraction of PS (at 76 %) because the more the PS chains, the higher the head–tail asymmetry . Herein, the head–tail asymmetry between the short hydrophilic head part and the long hydrophobic tail part in PEO‐based ABCP systems can be facilely adjusted through several methods to obtain structures of bicontinuous or inverse phases.…”

An Overview of Materials with Triply Periodic Minimal Surfaces and Related Geometry: From Biological Structures to Self‐Assembled Systems

“…Kim and co‐workers synthesized a series of branched block copolymers and investigated the effect of the architecture of the block copolymers on their solution self‐assembly into inverse mesophases . The precise control of the molecular shape from dendritic–linear to branched–linear to branched–branched by adjusting the solvent leads to the effective tuning of the molecular packing parameter and drives the block copolymer self‐assembly into vesicle, lamellar, inverse bicontinuous P and D cubic mesophases, and inverse hexagonal phases.…”

“…The precise control of the molecular shape from dendritic–linear to branched–linear to branched–branched by adjusting the solvent leads to the effective tuning of the molecular packing parameter and drives the block copolymer self‐assembly into vesicle, lamellar, inverse bicontinuous P and D cubic mesophases, and inverse hexagonal phases. It has been suggested that the branched shape of block copolymers plays an important role in the preferential self‐assembly into the D and P surface structures by affecting the chain dimensions of the hydrophobic block with respect to the bilayer plane . Very recently, Lin et al revealed that porous cubosomes with inverse P and D mesophases as well as hexasomes with inverse hexagonal structures can also be formed from simple block copolymers, such as PS‐ b ‐PEO.…”