Kehua Gu

Synthesis and sub-10 nm supramolecular self-assembly of a nanohybrid with a polynorbornene main chain and side-chain POSS moieties

A polynorbornene-based mesogen-jacketed liquid crystalline polymer (MJLCP) containing polyhedral oligomeric silsesquioxane (POSS) in the side chain, PNb10POSS, was synthesized through ring-opening metathesis polymerization. The chemical structure of the monomer was confirmed by 1H/13C NMR, high-resolution mass spectrometry, and elemental analysis. Molecular characterizations on the polymer were performed with 1H NMR, gel permeation chromatography, and thermogravimetric analysis. The phase behavior of this new organic–inorganic hybrid polymer was investigated by differential scanning calorimetry, polarized light microscopy, one-dimensional wide-angle X-ray scattering, synchrotron-radiation small-angle X-ray scattering (SAXS), two-dimensional wide-angle X-ray diffraction, and high-resolution transmission electron microscopy. With the competitive self-assemblies of the two covalently connected building blocks, namely MJLCP and POSS moieties, PNb10POSS shows various phase structures including an angstrom POSS crystal (Cr), a hexagonal columnar (Colh) phase and the Cr coexisting, and the Colh phase at different temperatures. The POSS crystal has a tremendous effect on the liquid crystalline (LC) behavior of the MJLCP. The results show that the competition between the crystallization of POSS and the LC formation of the polymer as a whole results in the complex phase behavior of the MJLCP-based nanohybrid. The polymer self-assembles into an organic–inorganic hybrid inclusion complex on the sub-10 nm scale. This work provides a new approach for the design and synthesis of ordered structures constructed by self-assembly on the sub-10 nm scale.

Hierarchical Self-Assembly of Disc-Rod Shape Amphiphiles Having Hexa-peri-hexabenzocoronene and a Relatively Long Rod

Two disc-rod shape amphiphiles consisting of hexa-peri-hexabenzocoronene (HBC) and a nanosized rodlike mesogen were designed and synthesized. Thermotropic phase behaviors were carefully studied. Despite significant steric mismatch between the discs and rods, hierarchical structures were observed for both disc-rod shape amphiphiles at ambient temperature and upon heating. Molecular packing schemes were proposed and confirmed using the reconstructed electron density maps, molecular dynamics simulation, and direct observation using transmission electron microscope. The results demonstrate that the shape effect is of great importance in the self-assembly of shape amphiphiles.

Hierarchically ordered structures of disk-cube triads containing hexa-peri-hexabenzocoronene and polyhedral oligomeric silsesquioxane

Obtaining nanoscale-ordered structures is important for the development of nanotechnology. We designed and synthesized a series of disk-cube triads containing one hexa-peri-hexabenzocoronene (HBC) and two polyhedral oligomeric silsesquioxane (POSS) moieties, HBC-2POSS. The two POSS units were linked via ester or amide bonds. With the amide linkage used, the hydrogen bonding that was introduced affected the balance between the π-π interaction of HBC cores and crystallization interaction of POSS units. Hierarchically ordered structures were obtained from HBC-2POSS triads owing to the synergistic effect of multiple secondary interactions: π-π interaction, hydrogen bonding, and crystallization interaction. As organic-inorganic hybrid materials, these HBC-2POSS triads are promising candidates for templates <10 nm.

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

The self-assembly of a rod-coil amphiphilic block copolymer (ABCP) led to Im3‾ m and Pn3‾ m polymer cubosomes and p6mm polymer hexasomes. This is the first time that these structures are observed in a rod-coil system. By varying the hydrophobic chain length, the initial concentration of the polymer solution, or the solubility parameter of the mixed solvent, head-tail asymmetry is adjusted to control the formation of polymer cubosomes or hexasomes. The formation mechanism of the polymer cubosomes was also studied. This research opens up a new way for further study of the bicontinuous and inverse phases in different ABCP systems.