Phase structure and molecular dynamics of liquid-crystalline side-on organosiloxane tetrapodes.
Phase structure and molecular dynamics of liquid-crystalline side-on organosiloxane tetrapodes.
复制标题
液晶侧有机硅氧烷四足体的相结构和分子动力学。
DOI：
--
复制
发表时间：
2010
期刊：
影响因子：
--
通讯作者：
G. Mehl
中科院分区：
文献类型：
--
作者：
D. Filip;C. Cruz;P. Sebastião;M. Cardoso;A. C. Ribeiro;M. Vilfan;T. Meyer;P. Kouwer;G. Mehl
X-ray diffraction and proton NMR relaxation measurements were carried out on two liquid-crystalline organosiloxane tetrapodes with side-on mesogenic groups, exhibiting nematic and smectic- C phases, and on a monomeric analog. Packing models for the mesophases exhibited by these systems are proposed on the basis of x-ray diffraction data. As a consequence of microsegregation, the aromatic cores are packed in between two sublayers formed by a mixture of interdigitated aliphatic and siloxane chains. The mixed sublayers are characteristic for the tetrapodes with side-on mesogenic groups presented in this work and have not been observed in tetrapodes with terminally attached mesogens. The tilt angle in the smectic- C phase is found very large, i.e., approximately 61 degrees -62 degrees . Notably, smectic- C clusters are present also in the whole temperature range of the nematic phase. NMR relaxometry yields T(1)-1 dispersions clearly different from those of conventional calamitics. The influence of molecular tendency to form interdigitated structures is evidenced by frequency-dependent relaxation rate in the isotropic phase-indicating the presence of ordered clusters far above the phase transition-and by the diminished role of molecular self-diffusion in ordered phases. Nematiclike director fluctuations are the dominating relaxation mechanism whereas the translational displacements are strongly hindered by the interdigitation of dendrimer arms.
