Methylene- and ether-linked liquid crystal dimers II. Effects of mesogenic linking unit and terminal chain length

Research output: Contribution to journalArticle

64 Citations (Scopus)

Abstract

Four series of liquid crystal dimers have been prepared containing either ether-linked or methylene-linked spacers. Changing the spacer from being ether-linked, i.e. O(CH2)(n)O, to methylene-linked, i.e. (CH2)(n+2), results in decreased nematic-isotropic transition temperatures, and this reduction is more pronounced for odd-membered spacers. By contrast, the entropy change associated with the nematic-isotropic transition is higher for an evenmembered methylene-linked dimer than for the corresponding ether-linked material. This trend is reversed for odd members. These observations are completely in accord with the predictions of a theoretical model developed by Luckhurst and co-workers in which the only difference between the dimers is their shape. For the highly non-linear pentamethylene-linked dimers, only those with a short terminal chain exhibited fluid smectic behaviour, specifically, a monotropic alternating SmC structure which allowed for the efficient packing of the bent molecules. Once the terminal chain reached a value of m=9, a modulated ordered smectic phase was observed. For even-membered dimers, which exhibit only nematic phases upon melting for short terminal chain lengths, smectic phase behaviour was promoted with increasing terminal chain length, as is conventionally observed. Even-membered ether-linked dimers exhibited a SmC phase whereas even-membered methylene-linked dimers exhibited an ordered smectic G/J phase. Thus, it would appear that the differences in the transitional properties of ether- and methylene-linked dimers can be accounted for largely in terms of geometrical factors.

Original languageEnglish
Pages (from-to)1499-1513
Number of pages14
JournalLiquid Crystals
Volume32
Issue number11
DOIs
Publication statusPublished - Nov 2005

Cite this

Methylene- and ether-linked liquid crystal dimers II. Effects of mesogenic linking unit and terminal chain length. / Henderson, Peter A.; Seddon, John M.; Imrie, Corrie T.

In: Liquid Crystals, Vol. 32, No. 11, 11.2005, p. 1499-1513.

Research output: Contribution to journalArticle

@article{31e60a3511fd44fda63d28945378274f,
title = "Methylene- and ether-linked liquid crystal dimers II. Effects of mesogenic linking unit and terminal chain length",
abstract = "Four series of liquid crystal dimers have been prepared containing either ether-linked or methylene-linked spacers. Changing the spacer from being ether-linked, i.e. O(CH2)(n)O, to methylene-linked, i.e. (CH2)(n+2), results in decreased nematic-isotropic transition temperatures, and this reduction is more pronounced for odd-membered spacers. By contrast, the entropy change associated with the nematic-isotropic transition is higher for an evenmembered methylene-linked dimer than for the corresponding ether-linked material. This trend is reversed for odd members. These observations are completely in accord with the predictions of a theoretical model developed by Luckhurst and co-workers in which the only difference between the dimers is their shape. For the highly non-linear pentamethylene-linked dimers, only those with a short terminal chain exhibited fluid smectic behaviour, specifically, a monotropic alternating SmC structure which allowed for the efficient packing of the bent molecules. Once the terminal chain reached a value of m=9, a modulated ordered smectic phase was observed. For even-membered dimers, which exhibit only nematic phases upon melting for short terminal chain lengths, smectic phase behaviour was promoted with increasing terminal chain length, as is conventionally observed. Even-membered ether-linked dimers exhibited a SmC phase whereas even-membered methylene-linked dimers exhibited an ordered smectic G/J phase. Thus, it would appear that the differences in the transitional properties of ether- and methylene-linked dimers can be accounted for largely in terms of geometrical factors.",
author = "Henderson, {Peter A.} and Seddon, {John M.} and Imrie, {Corrie T.}",
year = "2005",
month = "11",
doi = "10.1080/02678290500284983",
language = "English",
volume = "32",
pages = "1499--1513",
journal = "Liquid Crystals",
issn = "0267-8292",
publisher = "TAYLOR & FRANCIS LTD",
number = "11",

}

TY - JOUR

T1 - Methylene- and ether-linked liquid crystal dimers II. Effects of mesogenic linking unit and terminal chain length

AU - Henderson, Peter A.

AU - Seddon, John M.

AU - Imrie, Corrie T.

PY - 2005/11

Y1 - 2005/11

N2 - Four series of liquid crystal dimers have been prepared containing either ether-linked or methylene-linked spacers. Changing the spacer from being ether-linked, i.e. O(CH2)(n)O, to methylene-linked, i.e. (CH2)(n+2), results in decreased nematic-isotropic transition temperatures, and this reduction is more pronounced for odd-membered spacers. By contrast, the entropy change associated with the nematic-isotropic transition is higher for an evenmembered methylene-linked dimer than for the corresponding ether-linked material. This trend is reversed for odd members. These observations are completely in accord with the predictions of a theoretical model developed by Luckhurst and co-workers in which the only difference between the dimers is their shape. For the highly non-linear pentamethylene-linked dimers, only those with a short terminal chain exhibited fluid smectic behaviour, specifically, a monotropic alternating SmC structure which allowed for the efficient packing of the bent molecules. Once the terminal chain reached a value of m=9, a modulated ordered smectic phase was observed. For even-membered dimers, which exhibit only nematic phases upon melting for short terminal chain lengths, smectic phase behaviour was promoted with increasing terminal chain length, as is conventionally observed. Even-membered ether-linked dimers exhibited a SmC phase whereas even-membered methylene-linked dimers exhibited an ordered smectic G/J phase. Thus, it would appear that the differences in the transitional properties of ether- and methylene-linked dimers can be accounted for largely in terms of geometrical factors.

AB - Four series of liquid crystal dimers have been prepared containing either ether-linked or methylene-linked spacers. Changing the spacer from being ether-linked, i.e. O(CH2)(n)O, to methylene-linked, i.e. (CH2)(n+2), results in decreased nematic-isotropic transition temperatures, and this reduction is more pronounced for odd-membered spacers. By contrast, the entropy change associated with the nematic-isotropic transition is higher for an evenmembered methylene-linked dimer than for the corresponding ether-linked material. This trend is reversed for odd members. These observations are completely in accord with the predictions of a theoretical model developed by Luckhurst and co-workers in which the only difference between the dimers is their shape. For the highly non-linear pentamethylene-linked dimers, only those with a short terminal chain exhibited fluid smectic behaviour, specifically, a monotropic alternating SmC structure which allowed for the efficient packing of the bent molecules. Once the terminal chain reached a value of m=9, a modulated ordered smectic phase was observed. For even-membered dimers, which exhibit only nematic phases upon melting for short terminal chain lengths, smectic phase behaviour was promoted with increasing terminal chain length, as is conventionally observed. Even-membered ether-linked dimers exhibited a SmC phase whereas even-membered methylene-linked dimers exhibited an ordered smectic G/J phase. Thus, it would appear that the differences in the transitional properties of ether- and methylene-linked dimers can be accounted for largely in terms of geometrical factors.

U2 - 10.1080/02678290500284983

DO - 10.1080/02678290500284983

M3 - Article

VL - 32

SP - 1499

EP - 1513

JO - Liquid Crystals

JF - Liquid Crystals

SN - 0267-8292

IS - 11

ER -