Structure and molecular dynamics of the mesophases exhibited by an organosiloxane tetrapode with strong polar terminal groups
until further notice
SourcePhysical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 75, 1, (2007), pp. 011704-011704-11
Article / Letter to editor
Display more detailsDisplay less details
Spectroscopy of Solids and Interfaces
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
SubjectMolecular Materials; Spectroscopy of Solids and Interfaces
The polymorphism of a new organosiloxane tetrapode compound with cyano terminal polar groups was characterized by means of polarizing optical microscopy and x-ray diffraction. The compound exhibits smectic-A and smectic-C phases with a partial bilayer arrangement due to a certain degree of head-to-head association of the mesogenic units through their cyano end groups. On the basis of x-ray diffraction results, evidencing the microsegregation of polyphilic molecules, packing models for the smectic-A and smectic-C phases are proposed. A high degree of smectic positional order and a relatively low value of the tilt angle in the smectic-C phase are indicated. Molecular dynamics of the studied compound was investigated by means of proton NMR relaxometry. The frequency dispersions of the spin-lattice relaxation time (T-1) show that the relaxation is induced by three rotational modes of individual dendrimer arms with frequencies between 10(6) and 10(9) Hz. In the smectic phases, the effect of individual rotations is overwhelmed by a well expressed contribution of layer undulations at Larmor frequencies below similar to 10 MHz. The appearance of this relaxation mechanism over the frequency range of three decades is so far unique in the case of thermotropic liquid crystals. The analysis of the layer undulations contribution supports the microsegregation model of the smectic phases by revealing a slowing-down of translational diffusion and the lack of interactions among the sublayers formed by the mesogenic groups.
Upload full text
Use your RU credentials (u/z-number and password) to log in with SURFconext to upload a file for processing by the repository team.