Dielectric and visco-elastic properties of laterally fluorinated liquid crystal single compounds and their mixture

Comparative study of the mesomorphic properties of several laterally fluorinated liquid crystalline materials

“…Although, the threshold voltages of Compound 11 are found in the range~2 V, due to the low values of dielectric anisotropy the splay elastic constant values are found to be quite low throughout the mesomorphic range. [34] However, for Compounds 12 and 13 due to very small values of dielectric anisotropy, the Fréedericksz threshold was not found.…”

“…[33,34] However, for a comprehensive understanding and detailed comparison of the physical parameters, we present the results of these compounds (1,(9)(10)(11) as well, in this work.…”

“…These threshold voltage (V th ) values are used to determine the elastic constants. The temperature dependence of the bend elastic constant (K 33 ) of Compounds 1-10 are shown in Figure 3 The K 33 values in the nematic phase for Compounds 9 and 10 are around 7 pN and 8 pN, [34] respectively, and are found to increase quite steeply, especially as the N-SmB phase transition is approached (Figure 3(b)). Out of the three positive dielectric anisotropic compounds (11)(12)(13) only Compound 11 shows threshold behaviour in planar aligned cell.…”

“…It is observed that the dielectric anisotropy, Δε for Compounds 9 and 10 are around −2 at the nematic to SmB phase transition and −6 within the SmB phase. [34] This is due to the presence of only a single phenyl ring with conjugated π bonds in Compounds 9 and 10 in comparison to the terphenyl Compounds 1-8 which makes a significant contribution in the direction of the molecular long axis (ε ║ ). Compound 11, however, exhibits a positive dielectric anisotropy of around 1.…”

“…[45,46] From Figure 5(a) and (b) it is observed that the γ 1 values for Compounds 1-8 are around 90-120 mPas in the nematic range (near room temperature) which is considerably smaller than those obtained for phenyl bicyclohexane Compounds 9 and 10 with values of 233 mPas and 322 mPas, respectively, near the NSmB phase transition. [34] The geometry of a phenyl ring is planar, while a cyclohexane ring exhibits a highly non-planar structure. Hence, a molecule consisting of phenyl ring rotates more easily.…”