Oligomeric liquid crystals: From monomers to trimers

Henderson, Peter A.; Cook, A.G.; Imrie, Corrie T.

doi:10.1080/02678290412331298067

Cited by 95 publications

(33 citation statements)

References 41 publications

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“…These two lines diverge on increasing n such that a distinct oddeven effect in T N * I emerges for n = 10, 11 and 12 in which the even members exhibit the higher values. For a conventional series of nematogenic liquid crystal dimers, the values of T NI show a large odd−even effect on varying the length and parity of the flexible spacer in which the even members have the higher values but which attenuates with increasing spacer length [49]. Thus, T NI for the even members tend to lie on a smooth decreasing curve while those of the odd members tend to lie initially on an increasing curve, which passes through a maximum and then decreases.…”

Section: Resultsmentioning

confidence: 97%

Cholesteryl-based liquid crystal dimers containing a sulfur–sulfur link in the flexible spacer

Lee¹,

Lü²,

Henderson³

et al. 2012

Liquid Crystals

129

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Seven members of the homologous series of the liquid crystal dimers, the bis(ω-(cholesteryloxycarbonyl)alkyl) disulfides, which contain a sulfur−sulfur link in the flexible spacer have been synthesised and their liquid crystal properties characterised. The dimers are referred to using the acronym Chol-n-SS-n-Chol in which n denotes the number of carbon atoms linking the cholesteryl-based groups and the sulfur atoms, and was varied between 3, 5, 6, 8, 10, 11 and 12. All seven homologues exhibit a chiral nematic phase and for the longest three members a smectic A phase was also observed. An odd−even effect is apparent in both the transition temperatures and the values of the entropy change associated with the chiral nematic−isotropic transition, S N * I /R, in which dimers with even values of n show the higher values. This is interpreted in terms of the average molecular shapes in which the C−S−S−C dihedral angle is around 90 • . The values of S N * I /R shown by these dimers are very small for liquid crystal dimers and this is attributed to the increased molecular biaxiality arising from the C−S−S−C dihedral angle. The smectic A phase exhibited by the homologues with n = 10, 11 and 12 is proposed to consist of an intercalated arrangement of the dimers which is driven by the mismatch in cross-sectional areas of the cholesteryl-based groups and alkyl chains.

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Section: Resultsmentioning

confidence: 97%

Cholesteryl-based liquid crystal dimers containing a sulfur–sulfur link in the flexible spacer

Lee¹,

Lü²,

Henderson³

et al. 2012

Liquid Crystals

129

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“…The symbol " ≈ " indicates that the t-test could not distinguish between the population means of log(|J(-0.5V)|) for SC 15 and SC 16 at the 99% confidence level. While the values of μ log generally decrease with increasing chain length, the reversal of the inequalities between SC 11 and SC 12 and between SC 17 and SC 18 is a clear deviation from the trend observed in the separate odd and even datasets and, thus, constitutes one piece of evidence for an odd-even effect.…”

Section: The Sam Is At Least Partially Responsible For the Random Errmentioning

confidence: 99%

Odd−Even Effects in Charge Transport across Self-Assembled Monolayers

et al. 2011

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This paper compares charge transport across self-assembled monolayers (SAMs) of nalkanethiol containing odd and even numbers of methylenes. Ultraflat template-stripped silver (Ag TS ) surfaces supported the SAMs, while top-electrodes of eutectic galliumindium (EGaIn) contacted the SAMs to form metal/SAM//oxide/EGaIn junctions. TheEGaIn spontaneously reacts with ambient oxygen to form a thin (~ 2 nm) oxide layer.This oxide layer enabled EGaIn to maintain a stable, conical shape (convenient for forming microcontacts to SAMs) while retaining the ability to deform and flow upon contacting a hard surface. Conical electrodes of EGaIn conform (at least partially) to 2 SAMs, and generate high yields of working junctions. Ga 2 O 3 /EGaIn top electrodes enable the collection of statistically significant numbers of data in convenient periods of time. The observed difference in charge transport between n-alkanethiols with odd-and even-numbers of methylenes -the "odd-even effect" -is statistically discernable using these junctions, and demonstrates that this technique is sensitive to small differences in the structure and properties of the SAM. Alkanethiols with an even number of methylenes exhibit the expected exponential decrease in current density (J) with increasing chain length, as do alkanethiols with an odd number of methylenes. This trend disappears, however, when the two datasets are analyzed together; alkanethiols with an even number of methylenes typically show higher J than homologous alkanethiols with an odd number of methylenes. The precision of the present measurements, and the statistical power of the present analysis, were only sufficient to identify, with statistical confidence, the difference between an odd and even number of methylenes with respect to J, but not with respect to the tunneling decay constant, β, or the pre-exponential factor, J 0 .3

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“…Since LC dimers were firstly reported by Vorländer in 1927 [1], symmetrical dimers composed of two structurally identical mesogenic units linked through a flexible central spacer such as a polymethylene group have been widely investigated, especially during the past two decades [2][3][4][5]. The transition properties of LC dimers are known to depend on the nature and length of the flexible spacer [6][7][8]. For example, an odd-even effect for the clearing and melting points has been observed by changing the length of the spacer between the two mesogens.…”

Section: Introductionmentioning

confidence: 99%

The phase transition behaviour and electro-rheological effect of liquid crystalline siloxane dimers

et al. 2011

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Symmetrical liquid crystalline dimers have been synthesised, composed of rod-like mesogenic units with polar groups and a siloxane core of varying length in the central region. All the dimers containing siloxane units have been shown to exhibit a smectic A phase, confirmed by polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Rheological properties under an applied electric field were investigated by rotational rheometer. The influence of the siloxane core length on rheological properties has been investigated, and in addition the behaviour of the liquid crystalline dimers in the smectic A phase under an applied electric field has been observed by POM.

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Oligomeric liquid crystals: From monomers to trimers

Cited by 95 publications

References 41 publications

Cholesteryl-based liquid crystal dimers containing a sulfur–sulfur link in the flexible spacer

Cholesteryl-based liquid crystal dimers containing a sulfur–sulfur link in the flexible spacer

Odd−Even Effects in Charge Transport across Self-Assembled Monolayers

The phase transition behaviour and electro-rheological effect of liquid crystalline siloxane dimers

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