Two new series of compounds showing the ferroelectric nematic phase are reported, with the variation of terminal chain length. The temperature at which the axially polar N-F phase is formed decreases as the terminal chain length increases. For compounds with intermediate chain lengths, a wide temperature range nematic phase with antiferroelectric character emerges. Dielectric studies reveal both collective and non-collective fluctuations, with different behaviors observed in different phase transitions.
We report two new series of compounds that show the ferroelectric nematic, N-F, phase in which the terminal chain length is varied. The longer the terminal chain, the weaker the dipole-dipole interactions of the molecules are along the director and thus the lower the temperature at which the axially polar N-F phase is formed. For homologues of intermediate chain lengths, between the non-polar and ferroelectric nematic phases, a wide temperature range nematic phase emerges with antiferroelectric character. The size of the antiparallel ferroelectric domains critically increases upon transition to the N-F phase. In dielectric studies, both collective (ferroelectric) and non-collective fluctuations are present, and the ferroelectric mode softens weakly at the N-N-X phase transition because the polar order in this phase is weak. The transition to the N-F phase is characterized by a much stronger lowering of the mode relaxation frequency and an increase in its strength, and a typical critical behavior is observed.
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