Self-Assembly of Two-Dimensional Colloids in Spherical Space

Understanding the hierarchical organization of nanomaterials in different geometries is important for developing materials with new properties. It is well known that long-range ordering emerges when shape-anisotropic nanoparticles form liquid crystals; this may offer an opportunity to build large-scale ordered structures assembled by nanoparticles in a confined geometry. This study demonstrates the self-assembly of two-dimensional colloids of graphene oxide (GO) in a spherical space. The arrangements of GO nanosheets were captured by in situ photopolymerization to form microspheres, in which the nanosheets organized into lamellar liquid crystalline structures, adopting either a concentric configuration or a pseudo-concentric configuration, leaving topological defects in the central region. We also observed GO microspheres with bipolar-like configurations although they are scarce. Optical and electron microscopy observations revealed the fine structures of these topological defects caused by the frustration of liquid crystalline ordering in the spherical space. These results can help to understand the self-assembly behavior of two-dimensional colloids in confined geometries and may guide the development of functional materials or microdevices based on GO nanosheets.