Synthesis and Application of Liquid Crystalline Racemates as Dopants in Antiferroelectric Mixtures

Four liquid crystalline racemates, with oligomethylene spacer lengths of three and five and terminal alkyl chain carbon numbers of six and seven (acronyms 3PhPhC6, 5PhPhC6, 3PhPhC7, and 5PhPhC7), were synthesized. Racemates were characterized by their mesomorphic and thermodynamic properties. Identification of the liquid crystalline phases was performed using polarizing optical microscopy (POM), and the temperatures and enthalpies of phase transitions were determined by differential scanning calorimetry (DSC). Two selected racemates were used as dopants in antiferroelectric mixtures with investigated properties, and the effects of their addition on the mesomorphic properties of these mixtures were examined. The helical pitch of the doped mixtures was also measured using UV-Vis spectrophotometry. Racemates containing six carbon atoms in the alkyl chain (C6) exhibit the following phase sequence of Cr-SmCA-SmC-SmA-Iso, while racemates with seven carbon atoms (C7) exhibit the following phase sequence of Cr-SmC-SmA-Iso. Racemate-doped mixtures exhibit a very wide range of the antiferroelectric phase and slightly higher clearing points than the base mixtures. The helical pitch of the racemate-doped mixtures is longer than that of the base mixtures. Racemates containing seven carbon atoms in the alkyl chain have the potential to be used in the ferroelectric mixtures due to the absence of an anticlinic phase.