Nanospheres with Patches Arranged in Polyhedrons from Self- Assembly of Solution-State Diblock Copolymers under Spherical Confinement

Self-assembly of sphere-forming solution-state amphiphilic diblock copolymers under spherical nanopore confinement is investigated using a simulated annealing technique. For two types of cases of different pore-surface/copolymer interactions, sequences of self-assembled patchy nanospheres are obtained, and phase diagrams are constructed. Self-assembled patchy nanospheres with 1-21 solvophobic domains are observed. The outermost solvophobic domains (patches) are packed into various polyhedrons when their number is larger than 3, where three Platonic solids of a regular tetrahedron, an octahedron, and an icosahedron and seven Johnson solids of J12, J13, J17, J50, J51, J86, and J87 are identified. In addition, another Johnson solid of J84 is identified in a structure with two categories of B-domains. These polyhedrons have all or most of their faces in a triangular shape, and hence, they are closer to spherical in shape, which may relieve the chain stretching. Nanospheres with 1, 4, 6, 9, and 12 numbers of patches occur in relatively large windows in the phase diagrams of both types of cases. In one of the two types of cases, all nanospheres with any number of 1-14 patches occur in the phase diagram, whereas in the other type of cases, nanospheres with 2, 3, 5, 11, and 13 numbers of patches are absent in the phase diagram. Furthermore, at a given pore size, the number of patches changes nonmonotonically or is unchanged with an increase in the strength of the pore-surface/copolymer interactions for one type or the other type of case, respectively. Quantitative calculations are performed to elucidate mechanisms of the window size in the phase diagrams of nanospheres with different numbers of patches and structure details. All the observed phase behaviors can be well-explained based on the structure frustration, the conclusion being that the systems tend to avoid forming polyhedral structures with uneven distribution of solvophobic domains, and the differences between the two types of cases. Our results may provide a fundamental understanding of the relationship among confinement conditions, solvent conditions, and self-assembled structures.

Automated summary

The self-assembly of amphiphilic diblock copolymers under spherical nanopore confinement is studied using simulated annealing. Self-assembled patchy nanospheres with solvophobic domains are observed, and phase diagrams are constructed. Various polyhedrons are identified when the number of solvophobic domains is larger than 3, and their shapes are closer to spherical. Nanospheres with different numbers of patches occur in relatively large windows in the phase diagrams, but there are differences between the two types of cases. The relationship among confinement conditions, solvent conditions, and self-assembled structures is explained based on the observed phase behaviors.