Xue-Ming Liu

Thermomechanical properties of polyimide-epoxy nanocomposites from cubic silsesquioxane epoxides

Novel polyimide-epoxy organic–inorganic nanocomposites are prepared by in situ curing of polyamic acid macromolecules with two POSS epoxides, octa[(epoxycyclohexylethyl)dimethylsilyloxy]silsesquioxane (OC) and octa[(epoxyhexyl)dimethylsilyloxy]silsesquioxane (OH). Comparison between two series of nanocomposites from OC and OH provides a typical example of controlling the macro-scale properties by adjusting the nano-tether structure of the POSS molecules. DMA studies conclude that the crosslink densities of the polyimide-epoxy nanocomposites increase significantly; the nanocomposite networks are predominantly formed by the linkage between the terminal amine groups of the polyimide molecules and the epoxide groups of the POSS molecules. Furthermore, it is interesting to observe that although the crosslink densities of nanocomposites increase significantly, the compressive moduli, hardness and coefficients of thermal expansion change only slightly.

Trimeric supramolecular liquid crystals induced by halogen bonds

This paper described a series of trimeric halogen bonded supramolecular thermotropic liquid crystals. The halogen bonding interaction was studied by infrared and X-ray photoelectron spectroscopy. It was observed that the aromatic skeleton infrared vibration of halogen bonded acceptor molecules had moved to higher frequencies relative to their corresponding unbonded counterparts. The halogen-bonded acceptors showed higher N 1s binding energies of 0.89–1.12 eV than those of unbonded components. In contrast, the halogen-bonded donors displayed lower I 3d binding energies than their corresponding unbonded species. The changes in binding energies and in infrared frequencies demonstrated the presence of effective halogen bonding interaction. The thermal behaviors of the halogen-bonded complexes were examined using differential scanning calorimetry and optical polarizing microscopy. Most of the trimeric complexes exhibited thermotropic liquid crystals with smectic A phases. The effect of length in spacers and terminal groups in halogen bond molecules on mesophase transition temperatures was investigated, revealing that there was little correlation between the length in spacers and terminal groups and phase transition temperatures.