Effect of flip-flop motion on dielectric spectra of highly ordered liquid crystals

This paper presents studies of dielectric response of chosen Schiff bases, which have similar molecular structures with different isomerizations of an azomethine bridging group, alkyloxy chain length with $n=5$ or $n=6$ carbon atoms, and a bromine or chlorine halogen terminal atom. Significant differences in the values of the maximum of dielectric absorption related to flip-flop molecular jumps in hexagonal smectic-$B_{\mathrm{Cry}}$ phases have been found despite small differences of molecular dipole moments in these substances. This phenomenon is discussed in relation to the possibilities of the creation of dimers and to steric factors favoring motions.

Figure 1

Dielectric loss spectra in the Sm-$B_{\mathrm{Cry}}$ phase of several substances from the $n\mathrm{BBAA}$ homologues series at temperature given for each substance (for 5BBAA at 365 K, for 6BBAA at 369 K, for 8BBAA at 365 K, for 9BBAA at 374 K, and for 10BBAA at 366 K).

Figure 2

Dielectric loss spectra in the Sm-$B_{\mathrm{Cry}}$ phase of several substances from the $n\mathrm{CBAA}$ homologues series at temperature given for each substance (for 4CBAA at 363 K, for 5CBAA at 359 K, for 6CBAA at 363 K, for 11CBAA at 365 K, and for 12CBAA at 356 K).

Figure 3

Dielectric loss spectra in the Sm-$B_{\mathrm{Cry}}$ phase of several substances from the $n\mathrm{BACB}$ and the $n\mathrm{BABB}$ homologues series at temperature given for each substance (for 5BACB at 352 K, for 6BACB at 351 K, for 5BABB at 351 K, and for 6BABB at 361 K).

Figure 4

Different geometry of molecules in the dimers on the example of 5CBAA. Geometry presented at the point (1) corresponds to total energy of $E_1$, (2) to $E_2$, (3) to $E_3$, and so on.