| 초록 |
We have investigated the behavior of ultrathin films of an asymmetric dendrimeric material having tapered molecular architecture. Synchrotron X-ray diffraction (XRD), differential scanning calorimetry (DSC), polarized light microscopy (PLM) results show that the dendrimer exhibits hexagonal columnar mesophase upon cooling from isotropic phase. Transmission electron microscopy (TEM) images and X-ray reflectivity show that the columns are strongly affected by the substrates and film thickness: The columnar aligned perpendicular to hydrophobic substrate, and it align parallel to the hydrophilic surface. Different morphologies are encountered depending on the thickness. Thick films of such a material exhibit highly ordered hexagonal structure where the columns are oriented either parallel or perpendicular depending on the substrate. For thin films, they spontaneous form holes with straight edges aligned with hexagonal symmetry of orientation of the underlying molecular lattice. Further thinner films lead to a liquid-like disordered in-plane structure. Differences in domain morphology with film thickness can be attributed to the low surface energy planes, revealed by the faceting of discontinuous films. Other defects which occur in this system are also discussed, indicating flexible nature of the compound. |
