Odd-even effects in liquid crystals

ABSTRACT

In this paper, odd-even effects in liquid crystals are briefly summarised. Based on the position and type of the repeating units, odd-even effects can be caused by methylene (CH₂)_k units either when terminating the LC molecules or separating monomers in dimers or polymers, or by the parity of the number of rigid mesogenic units separated by odd numbered methylene spacers. These odd-even effects are manifested themselves in the transition temperatures (mainly of the clearing point) and transition entropies, but they can also lead to alteration of phases, such as antiferroelectric or ferroelectric, or the appearance of tilted or orthogonal mesophases. These alternating phase and entropy properties then also lead to alternating secondary properties, such as in birefringence and elastic properties. In each category, we also discuss the theoretical considerations that can explain the observed odd-even effects.

Graphical abstract

KEYWORDS:

• Liquid crystals
• odd-even effects
• phase transitions
• molecules

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was supported by the National Science Foundation under grant [DMR-1904167].