Self-assembled Nanostructures of Noncovalent Giant Amphiphilic Molecules Composed of Hydrophobic Isobutyl BPOSS and Hydrophilic POM in Different Cosolvents

The self-assembly of giant amphiphilic molecules with diverse topological structures has been widely investigated in bulk, solution, and interfacial environments because it can lead to interesting geometric patterns. However, many giant molecules or their self-assembling units are built by covalent bonds, which may limit the movement of the molecular blocks, affecting the self-assembly process and microstructure. In contrast, the self-assembly of giant units with noncovalent interactions can lead to interesting nanomorphologies and nanostructures. In this study, we built giant amphiphilic molecules (BPOSS&POM) by forming electrostatic interactions between hydrophobic isobutyl polyhedral oligomeric silsesquioxanes (BPOSSs) and hydrophilic polyoxometalates (POMs) to investigate the self-assembly behavior in water/acetone, water/THF, and hexane/acetone cosolvents. By controlling the solvent parameters, BPOSS&POM self-assembled into nanosheet, nanobelt, nanosphere, and nanocrumb structures. The morphology and detailed nanostructure of the different self-assemblies were revealed by performing transmission electron microscopy (TEM), scanning electron microscopy (SEM), and small-angle X-ray scattering (SAXS) measurements. The TEM and SAXS results indicated that the self-assembly microphase exhibited a lamellar structure and an interlayer distance of about 3 nm. The microphase structure of the self-assembly was alternatively organized by layers of BPOSS and POM according to their size and dimension. The polarity of the solvents substantially affected the morphology of the nanoassemblies but not the aggregation behavior of BPOSS and POM. This research offers insights into the preparation of nanomaterials with diverse micromorphologies by simply adjusting the solution components.