Morphological Diversity from the Solution Self-Assembly of Block Copolymer Blends Containing High Molecular-Weight Hydrophobic Blocks.

Self-assembled structures of high molecular-weight block copolymers (BCPs) can prematurely settle to local energy minima without reaching a time-averaged equilibrium, resulting in the emergence of intriguing morphologies, such as 3D micellar networks. This nonergodic behavior is evident in binary blends of BCPs with different molecular weights. This study reports the solution self-assembly of the blends of two branched-linear BCPs with similar block chemistries but different molecular weights of the hydrophobic blocks. A progressive transition of morphologies from hexosomes and cubosomes to 3D micellar networks, short cylinders, and spherical micelles is demonstrated, which is driven by the increase in the composition of low-molecular-weight BCP in the blend. The labeling of the micellar networks using Au nanoparticles confirms that lower molecular-weight BCP concentrates at the surface of micellar networks.

Templated synthesis of cubic crystalline single networks having large open-space lattices by polymer cubosomes.

The synthesis of biophotonic crystals of insects, cubic crystalline single networks of chitin having large open-space lattices, requires the selective diffusion of monomers into only one of two non-intersecting water-channel networks embedded within the template, ordered smooth endoplasmic reticulum (OSER). Here we show that the topology of the circumferential bilayer of polymer cubosomes (PCs)-polymeric analogues to lipid cubic membranes and complex biological membranes-differentiate between two non-intersecting pore networks embedded in the cubic mesophase by sealing one network at the interface. Consequently, single networks having large lattice parameters (>240 nm) are synthesized by cross-linking of inorganic precursors within the open network of the PCs. Our results pave the way to create triply periodic structures of open-space lattices as photonic crystals and metamaterials without relying on complex multi-step fabrication. Our results also suggest a possible answer for how biophotonic single cubic networks are created, using OSER as templates.

Solution self-assembly of block copolymers containing a branched hydrophilic block into inverse bicontinuous cubic mesophases.

Solution self-assembly of amphiphilic block copolymers into inverse bicontinuous cubic mesophases is an emerging strategy for directly creating highly ordered triply periodic porous polymer nanostructures with large pore networks and desired surface functionalities. Although there have been recent reports on the formation of highly ordered triply periodic minimal surfaces of self-assembled block copolymer bilayers, the structural requirements for block copolymers in order to facilitate the preferential formation of such inverse mesophases in solution have not been fully investigated. In this study, we synthesized a series of model block copolymers, namely, branched poly(ethylene glycol)-block-polystyrene (bPEG-PS), to investigate the effect of the architecture of the block copolymers on their solution self-assembly into inverse mesophases consisting of the block copolymer bilayer. On the basis of the results, we suggest that the branched architecture of the hydrophilic block is a crucial structural requirement for the preferential self-assembly of the resulting block copolymers into inverse bicontinuous cubic phases. The internal crystalline lattice of the inverse bicontinuous cubic structure can be controlled via coassembly of branched and linear block copolymers. The results presented here provide design criteria for amphiphilic block copolymers to allow the formation of inverse bicontinuous cubic mesophases in solution. This may contribute to the direct synthesis of well-defined porous polymers with desired crystalline order in the porous networks and surface functionalities.