Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Jan;81(1):011702. doi: 10.1103/PhysRevE.81.011702. Epub 2010 Jan 19.

Phase structure and molecular dynamics of liquid-crystalline side-on organosiloxane tetrapodes.

Physical review. E, Statistical, nonlinear, and soft matter physics

D Filip, C Cruz, P J Sebastião, M Cardoso, A C Ribeiro, M Vilfan, T Meyer, P H J Kouwer, G H Mehl

PMID: 20365386 DOI: 10.1103/PhysRevE.81.011702

Abstract

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.

Publication Types

• Journal Article
• Research Support, Non-U.S. Gov't