2 research outputs found
Shape and Confinement Effects of Various Terminal Siloxane Groups on Supramolecular Interactions of Hydrogen-Bonded Bent-Core Liquid Crystals
To investigate the shape and confinement
effects of the terminal
siloxane groups on the self-assembled behavior of molecular arrangements
in hydrogen-bonded (H-bonded) bent-core complexes, four H-bonded bent-core
complexes <b>S1</b>, <b>P1</b>, <b>C4</b>, and <b>P8</b> with string-, ring-, and cage-like siloxane termini (i.e.,
linear siloxane unit −Si–O–Si–O–Si–,
cyclic siloxane unit (Si–O)<sub>4</sub>, and silsesquioxane
unit POSS, respectively) were synthesized and investigated. By X-ray
diffraction measurements, different types of SmCG (B8) phases and
leaning angles were controlled by the shape effect of the string-
and cage-like siloxane termini for <b>S1</b> and <b>P1</b> (with only one arm of H-bonded bent-core), respectively. In addition,
the confinement effect of <b>P1</b>, <b>C4</b>, and <b>P8</b> (accompanied by increasing the numbers of attached H-bonded
bent-core arms) resulted in higher transition temperatures and the
diminishing of mesophasic ranges (even the disappearance of mesophase
in <b>P8</b>). Moreover, AFM images showed the bilayer smectic
CG phases of <b>S1</b> and <b>P1</b> were aligned to reveal
highly ordered thread-like structures by a DC field. By spontaneous
polarization measurements within the mesophasic ranges, <b>S1</b> and <b>P1</b> showed ferroelectric transitions but <b>C4</b> displayed antiferroelectricity. Finally, the electro-optical performance
of B8 phases could be optimized through binary mixtures of <b>S1</b> and <b>P1</b>, and a well aligned modulated ribbon phase could
be formed via specific molar ratios of the binary mixtures
Broad Ranges and Fast Responses of Single-Component Blue-Phase Liquid Crystals Containing Banana-Shaped 1,3,4-Oxadiazole Cores
In this study, we synthesized two
novel 1,3,4-oxadiazole-based bent-core liquid crystals (<b>OXD7*</b>, <b>OXD5B7F*</b>) containing a chiral tail that display broad
ranges of the blue phase III (34 and 7 K, respectively); we characterized
them using polarized optical microscopy, differential scanning calorimetry,
and circular dichroism. The electro-optical responses of both of these
liquid crystals are much faster than those of previously reported
single-component blue-phase liquid crystals. To optimize its electro-optical
performance, we mixed <b>OXD7*</b> (the blue-phase range of
which is broader than that of <b>OXD5B7F*</b>) with its analogue <b>OXD6</b> (at weight ratios of 6:4 and 4:6). We also performed
molecular modeling of single-component BPLCs (<b>OXD7*</b> and <b>OXD5B7F*</b>) to analyze the possible parameters affecting their
blue phase ranges