Dendrimeric Liquid Crystals:  Isotropic−Nematic Pretransitional Behavior

Abstract

Kerr measurements, ellipsometry, and quasielastic light scattering have been used to probe nematic fluctuations and nematic wetting at an isotropic liquid crystal−substrate interface in four generations of liquid crystalline monodendrons and dendrimers. We find that the pretransitional behavior is qualitatively similar to that of low molecular weight liquid crystals, exhibiting a Landau-like divergence of the relaxation time and a logarithmic divergence of the optical retardation on approaching the nematic−isotropic phase transition from above. Quantitatively, we find that the transition temperatures of the monodendrons are typically about 0.5 K above the supercooling limit of the isotropic phase and that the orientational viscosities may be fit to a power law in molecular weight M n, where the exponent ≤ 1.0.

Chirality transfer in nematic liquid crystals doped with (S)-naproxen-functionalized gold nanoclusters: an induced circular dichroism study

“…1(a)]. 30 These cells were then filled with the mixtures at a temperature above the clearing point of 5CB (ca. 40 uC), and then slowly cooled down to the N phase at a cooling rate of 1 uC min 21 .…”

Convergent Dendrons and Dendrimers: from Synthesis to Applications

“…Because the repeat units comprise the majority of the dendritic structure, they represent an ideal location for multiple functional moieties. In addition to the numerous examples of conjugated dendrimers previously discussed, 115,116,[119][120][121][122][124][125][126][127][128][129][130][132][133][134][140][141][142][143][144][145][146][147][148]497 the convergent approach has been demonstrated as a viable route toward the preparation of dendrimers with a range of repeat units including: fullerene, 498,499 quaternary ammonium salt, 177 pyridine, 382,500-502 TTF, 503-506 triarylamine, [171][172][173]507,508 carbazole, 509,510 azobenzene, 351,511-513 liquid crystalline, [514][515][516] and chiral repeat units. [96][97][98][99][100][101][102]…”

Dendrimers in Supramolecular Chemistry: From Molecular Recognition to Self-Assembly

“…In spite of this encouraging result, there are drawbacks of the hyperbranched polymer approach, mainly due to the high polydispersities and, in this specific case, impurities resulting from intramolecular alkylation or elimination. Thus, Percec and co-workers , synthesized pure dendritic materials on the basis of the repeat unit 40 using an iterative convergent strategy similar to that of Fréchet. Mono- and tridendrons up to the fourth generation were prepared with 10-undecenyl groups on the periphery and their properties were investigated by using DSC, polarizing optical microscopy (POM), and X-ray diffraction (XRD).…”