Refine
Has Fulltext
- no (16)
Document Type
- Article (15)
- Monograph/Edited Volume (1)
Is part of the Bibliography
- yes (16)
An increase in random molecular vibrations of a solid owing to heating above the melting point leads to a decrease in its long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. Here we report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular polarized light the film behaves as an isotropic viscoelastic fluid, it shows considerable fluidity only in the direction parallel to the light field vector under linear polarized light. The fluidization phenomenon is related to photoinduced motion of azobenzene-functionalized molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. We also describe here how the photofluidization allows nanoscopic elements of matter to be precisely manipulated
The surface structures of crystals based on aromatic oxadiazoles were investigated by AFM. The crystal structure for 2,5-di(p-tolyl)-1,3,4-oxadiazole (DTO) differs from that of 2,5-di (4-methoxycarbonyl-phenyl)-1,3,4- oxadiazole (DMPO). In DMPO all molecules show parallel orientation to the surface in such a way that the surface is formed as well as by the nitrogen atoms of the heterocyclic rings and the methyl groups of the ester substituents. By contrast, the oxadiazole molecules in DTO crystals are oriented perpendicular to the crystal surface. The experimental data are interpreted by molecular modelling. It is shown that there is a difference between molecular structure of the surface, as detected by AFM, and the bulk structure determined by X-ray diffraction.