FIG 3 - uploaded by Patrick Oswald
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We show experimentally and theoretically that the heliconical fluctuations that develop in a cholesteric phase (Ch) close to a transition to a chiral twist-bend nematic phase (N_{TB}) may lead to the appearance of a compensation point. At this point, the equilibrium twist of the cholesteric phase vanishes and changes sign. Mixtures of the flexible...
Contexts in source publication
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... chiral molecules used were R811 (R-(+)-octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy) benzoate, Fig. 3(a)), CB15 (R-(+)-4'-(2-methylbutyl)-[1,1'-biphenyl]-4-carbonitrile, Fig. 3(b)), S2011 (S-(−)-4-(3,5-difluoro-4-(octan-2-yloxy)phenyl-4'-propyl-1,1'-bi(cyclohexane), Fig. 3(c)) and CC (cholesteryl chloride, Fig. ...
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... chiral molecules used were R811 (R-(+)-octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy) benzoate, Fig. 3(a)), CB15 (R-(+)-4'-(2-methylbutyl)-[1,1'-biphenyl]-4-carbonitrile, Fig. 3(b)), S2011 (S-(−)-4-(3,5-difluoro-4-(octan-2-yloxy)phenyl-4'-propyl-1,1'-bi(cyclohexane), Fig. 3(c)) and CC (cholesteryl chloride, Fig. ...
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... chiral molecules used were R811 (R-(+)-octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy) benzoate, Fig. 3(a)), CB15 (R-(+)-4'-(2-methylbutyl)-[1,1'-biphenyl]-4-carbonitrile, Fig. 3(b)), S2011 (S-(−)-4-(3,5-difluoro-4-(octan-2-yloxy)phenyl-4'-propyl-1,1'-bi(cyclohexane), Fig. 3(c)) and CC (cholesteryl chloride, Fig. ...
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... chiral molecules used were R811 (R-(+)-octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy) benzoate, Fig. 3(a)), CB15 (R-(+)-4'-(2-methylbutyl)-[1,1'-biphenyl]-4-carbonitrile, Fig. 3(b)), S2011 (S-(−)-4-(3,5-difluoro-4-(octan-2-yloxy)phenyl-4'-propyl-1,1'-bi(cyclohexane), Fig. 3(c)) and CC (cholesteryl chloride, Fig. ...
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... for instance at T − T NB = 30 • C for the mixture M1) must be the same for all the chiral molecules provided that q 0 is the same in absolute value. To check this point, we compared a mixture of M1 + R811 with a mixture of M1 + CC. These two chiral molecules were chosen on purpose because they are chemically very different, as can be seen in Fig. 3, and of opposite handedness. We prepared a mixture of M1 + 0.88 wt% CC. This concentration was chosen in order that q 0 be the same in absolute value as the one of the mixture M1 + 0.182 wt% R811 (see Fig. 4(a)). We then measured the curve q(T ) for this new mixture and we reported on the same graph in Fig. 11 the curves q/q 0 as a ...
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... chiral molecules used were R811 (R-(+)-octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy) benzoate, Fig. 3(a)), CB15 (R-(+)-4'-(2-methylbutyl)-[1,1'-biphenyl]-4-carbonitrile, Fig. 3(b)), S2011 (S-(−)-4-(3,5-difluoro-4-(octan-2-yloxy)phenyl-4'-propyl-1,1'-bi(cyclohexane), Fig. 3(c)) and CC (cholesteryl chloride, Fig. ...
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... chiral molecules used were R811 (R-(+)-octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy) benzoate, Fig. 3(a)), CB15 (R-(+)-4'-(2-methylbutyl)-[1,1'-biphenyl]-4-carbonitrile, Fig. 3(b)), S2011 (S-(−)-4-(3,5-difluoro-4-(octan-2-yloxy)phenyl-4'-propyl-1,1'-bi(cyclohexane), Fig. 3(c)) and CC (cholesteryl chloride, Fig. ...
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... chiral molecules used were R811 (R-(+)-octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy) benzoate, Fig. 3(a)), CB15 (R-(+)-4'-(2-methylbutyl)-[1,1'-biphenyl]-4-carbonitrile, Fig. 3(b)), S2011 (S-(−)-4-(3,5-difluoro-4-(octan-2-yloxy)phenyl-4'-propyl-1,1'-bi(cyclohexane), Fig. 3(c)) and CC (cholesteryl chloride, Fig. ...
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... chiral molecules used were R811 (R-(+)-octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy) benzoate, Fig. 3(a)), CB15 (R-(+)-4'-(2-methylbutyl)-[1,1'-biphenyl]-4-carbonitrile, Fig. 3(b)), S2011 (S-(−)-4-(3,5-difluoro-4-(octan-2-yloxy)phenyl-4'-propyl-1,1'-bi(cyclohexane), Fig. 3(c)) and CC (cholesteryl chloride, Fig. ...
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... for instance at T − T NB = 30 • C for the mixture M1) must be the same for all the chiral molecules provided that q 0 is the same in absolute value. To check this point, we compared a mixture of M1 + R811 with a mixture of M1 + CC. These two chiral molecules were chosen on purpose because they are chemically very different, as can be seen in Fig. 3, and of opposite handedness. We prepared a mixture of M1 + 0.88 wt% CC. This concentration was chosen in order that q 0 be the same in absolute value as the one of the mixture M1 + 0.182 wt% R811 (see Fig. 4(a)). We then measured the curve q(T ) for this new mixture and we reported on the same graph in Fig. 11 the curves q/q 0 as a ...
Citations
... As expected, the pitch is almost constant at high temperature (close to −145 µm at T NI ) and it strongly increases (in absolute value) -without diverging-upon approaching the N TB phase. This result agrees with previous measurements in the vicinity of the N TB phase [20,21]. In addition, we measured the helical twist power (HTP) of the chiral molecule R811 in C15. ...
The structure of the nematic (cholesteric) drops that form at the clearing temperature of a mixture of the bent-core molecule CB7CB and the rodlike molecule 8CB doped with a surfactant is optically determined. Using experimental observations and numerical simulations, it is demonstrated that the director field inside these drops is not escaped concentric, as previously proposed, but twisted bipolar. The Lehmann rotation of these drops in the presence of a temperature gradient is described. Their rotation velocity is shown to be proportional to the temperature gradient and to the surface twist angle of the director field and inversely proportional to the drop radius, thus revealing a fundamental scaling law for the Lehmann effect of nematic and cholesteric twisted-bipolar droplets.
... Since in some cases the Grandjean-Cano wedge approach could produce incorrect results if attention is not being paid to the Burgers vector of the dislocations [22] and to their locations [23,24], we verified the value of P 0 in an independent experiment by measuring the wavelength of Bragg reflection peaks at oblique incidence for a planar Ch cell with d = 16 μm at T = 19 • C [ Fig. 5(b)]. At the fixed angle of incidence β = 65 • , we use the p-polarized incident beam and s-polarized reflected beam to obtain the spectrum with two reflection maxima, λ =n( P 0 m ) cos β LC that correspond to m = 4 and 6, i.e., to P 0 /4 and P 0 /6 values; the angle of light propagation in the liquid crystal β LC is calculated using Snell's law, β LC = arcsin[(n g /n) sin β], wheren is the average of refractive indices, and n g = 1.52 (at 600 nm) is the refractive index of the soda-lime glass. ...
... These dependencies are of interest on their own, as both K 22 and especially K 33 increase rapidly near the Ch − N * TB transition [ Fig. 9(a)]. Similar behavior is known in nematics [17,23,27,28] and cholesterics [6,24] that show a transition to N TB or N * TB . The increase of K 22 and K 33 is also well established in materials in which the nematic [29] or cholesteric [5] phase experiences a transition into a smectic A phase. ...
... The intrinsic (field-free) pitch P 0 of the Ch increases as the temperature is lowered (Fig. 5). Similar behavior of the Ch pitch is observed near the transition to the smectic A [5] and N * TB phase [24,30]. The trend could be again explained by the proximity to pseudolayered N TB and N * TB phases, but Oswald and Dequidt [24] proposed an additional mechanism, rooted in the possibility that N * TB nuclei impose an opposite sense of chirality onto the surrounding Ch background [24]. ...
Unique electro-optical properties of the oblique helicoidal cholesteric (Ch_{OH}) stem from its heliconical director structure. An applied electric field preserves the single-harmonic modulation of the director while tuning the Ch_{OH} period and the corresponding Bragg-peak wavelength within a broad spectral range. We use the response of Ch_{OH} to the electric field to measure the elastic constants of twist K_{22} and bend K_{33} directly in the cholesteric phase. The temperature dependencies of K_{22} and K_{33} allow us to determine the range of the electric tunability of the Ch_{OH} pitch and the heliconical angle. The data are important for understanding how molecular composition and chirality influence macroscopic elastic properties of the chiral liquid crystals and for the development of Ch_{OH}-based optical devices.
