Anomalies in the twist elastic behaviour of mixtures of calamitic and bent-core liquid crystals

Figures & data

Table 1. Compositions of the pure materials and mixtures with the phase temperatures determined on cooling, where Iso = isotropic phase, N = nematic phase, SmX = smectic phase of unknown type, Cr = crystal phase, N + F = nematic phase with filaments, SmA = smectic A phase and SmA+F = smectic A phase with filaments. The elastic constants of the pure materials and the mixtures are all given in the results section. Synthesis of compound 1 is available from the linked data repository https://doi.org/10.5518/482.

Materials	Composition	Phase transitions/°C
Compound 1		Iso 115 N 88 SmX 64 Cr
Compound 2		Iso 230 N 170 DC 100 Cr
5CB		Iso 35 N 18 Cr
8CB		Iso 40 N 33.5 SmA 21.5 Cr
ZLI 1132	Merck proprietary mixture	Iso 71.2 N
Mixture 1	10:90 C1:5CB	Iso 42.0 N
Mixture 2	10:90 C1:8CB	Iso 46.3 N 29.8 SmA
Mixture 3	10:90 C1:ZLI 1132	Iso 72.5 N
Mixture 4	10:90 C2:5CB	Iso 49.0 N 26.1 N + F
Mixture 5	10:90 C2:8CB	Iso 52.0 N 40.0 N + F 38.4 SmA+F
Mixture 6	10:90 C2:ZLI 1132	Iso 80.7 N

Figure 1. (Colour online) Histogram showing the phase transitions with the transition temperatures determined on cooling for mixtures 1–6. Everything above the bars indicates the isotropic phase, with the dark blue bars representing the nematic phase, the light blue bar represents the nematic phase with filaments, the orange bars represent the smectic A phase and the light orange bar represents the smectic A phase with filaments.

Figure 2. (Colour online) Dielectric anisotropy, Δε as a function of T-T_NI for 5CB (orange upward triangles), mixture 1 (blue crossed) and mixture 4 (magenta diamonds).

Figure 3. (Colour online) (a) The splay, K₁₁ (a), twist, K₂₂ (b) and bend, K₃₃ (c) elastic constants as a function of T-T_NI for compound 1 [16] (maroon asterisks), compound 2 [29] (green squares), 5CB (orange upward triangles), mixture 1 (blue crosses) and mixture 4 (magenta diamonds).

Figure 4. (Colour online) Dielectric anisotropy, Δε as a function of T-TNI for 8CB (grey downward triangles), mixture 2 (black pentagrams) and mixture 5 (red circles).

Figure 5. (Colour online) (a) The splay, K₁₁ (a), twist, K₂₂ (b) and bend, K₃₃ (c) elastic constants as a function of T-T_NI for compound 1 [16] (maroon asterisks), compound 2 [29] (green squares), 8CB (grey downward triangles), mixture 2 (black pentagrams) and mixture 5 (red circles).

Figure 6. (Colour online) (a) The splay, K₁₁ (a), twist, K₂₂ (b) and bend, K₃₃ (c) elastic constants as a function of T-T_NI for compound 1 [16] (maroon asterisks), compound 2 [29] (green squares), ZLI 1132 (light blue dots), mixture 3 (black circles) and mixture 6 (red diamonds).

Srigengan S, Nagaraj M, Ferrarini A, et al. Anomalously low twist and bend elastic constants in an oxadiazole-based bent-core nematic liquid crystal and its mixtures; contributions of spontaneous chirality and polarity. J Mater Chem C. 2018;6:980–988.

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Kaur S, Tian L, Liu H, et al. The elastic and optical properties of a bent-core thiadiazole nematic liquid crystal: the role of the bend angle. J Mater Chem C. 2013;1:2416–2425.

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