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On the structure of the Nx phase of symmetric dimers: inferences from NMR

December 19th, 2014 Comments off
Anke Hoffmann,   Alexandros G. Vanakaras,   Alexandra Kohlemeir,   Georg H. Mehl and   Demetri J. Photinos
Soft Matter, 11, 850-855, 2015. DOI: 10.1039/C4SM02480J (download:
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Abstract: NMR measurements on a selectively deuterated liquid crystal dimer CB-C9-CB, exhibiting two nematic phases, show that the molecules in the lower temperature nematic phase, NX, experience a chiral environment and are ordered about a uniformly oriented director throughout the macroscopic sample. The results are contrasted with previous interpretations that suggested a twist-bend spatial variation of the director. A structural picture is proposed wherein the molecules are packed into highly correlated chiral assemblies.
Categories: 2014, A. G. Vanakaras, D.J. Photinos, Paper Tags:

Surface-Induced Ordering on Model Liquid Crystalline Dendrimers

December 5th, 2014 Comments off

Zerihun G. Workineh and Alexandros G. Vanakaras, Polymers 2014, 6(8), 2082-2099; doi:10.3390/polym6082082

Abstract: The surface alignment of liquid crystalline dendrimers (LCDrs) is a key factor for many of their potential applications. Here, we present results from Monte Carlo simulations of LCDrs adsorbed on flat, impenetrable aligning substrates. A tractable coarse-grained force field for the inter-dendritic and the dendrimer-substrate interactions is introduced. We investigate the conformational and ordering properties of single, end-functionalized LCDrs under homeotropic, random (or degenerate) planar and unidirectional planar aligning substrates. Depending on the anchoring constrains to the mesogenic units of the LCDr and on temperature, a variety of stable ordered LCDr states, differing in their topology, are observed and analyzed. The influence of the dendritic generation and core functionality on the surface-induced ordering of the LCDrs are examined.

Keywords: liquid crystal dendrimers; surface alignment; Monte Carlo simulations; surface confinement of dendrimer

Categories: 2014, A. G. Vanakaras, Z. Workineh Tags:

On the structure of the Nx phase of symmetric dimers

December 4th, 2014 Comments off

Anke Hoffmann, Alexandros G. Vanakaras, Alexandra Kohlmeier, Georg H. Mehl, Demetri J. Photinos, arXiv:1401.5445 [cond-Mat]. (2014). http://arxiv.org/abs/1401.5445.

Abstract: NMR measurements on a selectively deuteriated liquid crystal dimer CB-C9-CB exhibiting two nematic phases show that the molecules in the lower temperature nematic phase, Nx, experience a chiral environment and are ordered about a unique direction. The results are contrasted with previous reports that proposed a twist-bend spatial variation of the director. A structural model is proposed wherein the molecules show organization into highly correlated assemblies of opposite chirality.

Categories: 2014, A. G. Vanakaras, D.J. Photinos Tags: