Recovery of a reversed phase sequence in one ternary liquid-crystal-mixture system

The $n\text{OHFBBB}1\text{M}7$ $\left(n=10\right)$ compound, 10OHF, shows a reversed $\text{Sm}{C}_{FI2}^{\ast }\text{-Sm}{C}^{\ast }$ phase sequence, unique among all known antiferroelectric liquid crystals. This reversed phase sequence is stabilized when 10OHF is doped with 9OTBBB1M7(C9) or 11OTBBB1M7(C11). In contrast, doping of the homologous members ($n=9$, 11, or 12) eliminates the $\text{Sm}{C}_{FI2}^{\ast }$ phase. One 10OHF/11OHF mixture without the $\text{Sm}{C}_{FI2}^{\ast }$ phase was selected for further studies. By adding C9 into this particular mixture, the reversed phase sequence is revived. To our surprise, even though 11OHF destabilizes the $\text{Sm}{C}_{FI2}^{\ast }$ phase in binary mixtures with 10OHF, it significantly increases the $\text{Sm}{C}_{FI2}^{\ast }$ temperature range in the 10OHF/11OHF/C9 ternary mixtures.

Figure 1

(Color online) $\Delta$ as a function of temperature for a 56-layer film of 75% 10OHF/25% 11OHF mixture from NTE while cooling at $0.1°\text{C}/\text{min}$. $\alpha$ is the angle between the $\mathbf{E}$ orientation and the incident plane of the laser light.

Figure 2

(Color online) Phase diagram of $10{\text{OHF}}_{1-u}$, $9{\text{OHF}}_u$, and $10{\text{OHF}}_{1-v}$ $11{\text{OHF}}_v$ mixtures. On the top is the chemical structure of $n\text{OHFBBB}1\text{M}7\left(n\text{OHF}\right)$. The phase sequences of 9OHF and 11OHF are $\text{Sm}A$ $\left(63°\text{C}\right)$ $\text{Sm}{C}_{\alpha }^{\ast }$ $\left(52°\text{C}\right)$ $\text{Sm}{C}^{\ast }$ and $\text{Sm}A$ $\left(94°\text{C}\right)$ $\text{Sm}{C}_{\alpha }^{\ast }$ $\left(89°\text{C}\right)$ $\text{Sm}{C}^{\ast }$.

Figure 3

(Color online) Phase diagram of ${\left(73\%10\text{OHF}/27\%11\text{OHF}\right)}_{1-x}\text{C}{9}_x$ mixtures. The crosses mark the temperatures at which RXRD was performed. On the top is the chemical structure of 9OTBBB1M7(C9). The phase sequence of C9 is $\text{Sm}A$ $\left(115°\text{C}\right)$ $\text{Sm}{C}_{\alpha }^{\ast }$ $\left(109°\text{C}\right)$ $\text{Sm}{C}_{FI2}^{\ast }$ $\left(85°\text{C}\right)$ $\text{Sm}{C}_A^{\ast }$. The disappearance of the $\text{Sm}{C}_{\alpha }^{\ast }\text{-Sm}{C}_{FI2}^{\ast }$ transition below 10% C9 mixture is not an important issue for this paper. Without any data in this range, we represent this part of phase boundary by a dashed line.

Figure 4

Temperature ranges of the $\text{Sm}{C}_{FI2}^{\ast }$ phase in the ternary ${\left(73\%10\text{OHF}/27\%11\text{OHF}\right)}_{1-x}\text{C}{9}_x$ mixtures and in the binary ${\left(10\text{OHF}\right)}_{1-x}\text{C}{9}_x$ mixtures as a function of C9 concentration $\left(x\right)$.

Figure 5

(Color online) (a) The pitch temperature evolution of the ${\left(73\%10\text{OHF}/27\%11\text{OHF}\right)}_{0.85}\text{C}{9}_{0.15}$ ternary mixture in the $\text{Sm}{C}_{\alpha }^{\ast }$ phase measured by RXRD. [(b)–(d)] Scans of the same mixture at $92.2°\text{C}$, $84.2°\text{C}$ and $81.2°\text{C}$.