Condensation of free volume in structures of nematic and hexatic liquid crystals

TY - JOUR

T1 - Condensation of free volume in structures of nematic and hexatic liquid crystals

AU - Mandle, Richard

AU - Stock, Nina

AU - Cowling, Stephen James

AU - Parker, Rachel Roberta

AU - Hart, Sam J.

AU - Whitwood, Adrian C.

AU - Goodby, John William

N1 - © 2018 The Author(s).

PY - 2019

Y1 - 2019

N2 - Eight novel liquid crystalline materials were prepared containing highly branched terminal chains, either 2,4,4-trimethylpentyl or 3,5,5-trimethylhexyl. All materials exhibit nematic mesophases, with additional smectic (Sm) C, hexatic B and SmI phases for certain homologues. Analysis by small- and wide-angle X-ray scattering reveals continual build-up of the correlation length within the nematicphases, where we also observe splitting of the small angle peak into four lobes, indicating pretransitional Sm fluctuations. Connoscopy confirms the nematic phase to be uniaxial and optically positive. We observe that in the solid state, the molecules exist as staggered antiparallel pairs as a consequence of the sterically demanding bulky terminal group, and this would also appear to manifest inthe hexatic B phase, where the layer spacing was found to be greater than the molecular length. If true, this is an example of pair formation driven by sterics rather than dipole–dipole interactions and suggests that reentrant systems driven purely by steric frustration may be found.

AB - Eight novel liquid crystalline materials were prepared containing highly branched terminal chains, either 2,4,4-trimethylpentyl or 3,5,5-trimethylhexyl. All materials exhibit nematic mesophases, with additional smectic (Sm) C, hexatic B and SmI phases for certain homologues. Analysis by small- and wide-angle X-ray scattering reveals continual build-up of the correlation length within the nematicphases, where we also observe splitting of the small angle peak into four lobes, indicating pretransitional Sm fluctuations. Connoscopy confirms the nematic phase to be uniaxial and optically positive. We observe that in the solid state, the molecules exist as staggered antiparallel pairs as a consequence of the sterically demanding bulky terminal group, and this would also appear to manifest inthe hexatic B phase, where the layer spacing was found to be greater than the molecular length. If true, this is an example of pair formation driven by sterics rather than dipole–dipole interactions and suggests that reentrant systems driven purely by steric frustration may be found.

KW - Liquid crystals

KW - SAXS

KW - hexatic phases

KW - smectic phases

UR - http://www.scopus.com/inward/record.url?scp=85047314811&partnerID=8YFLogxK

U2 - 10.1080/02678292.2018.1475686

DO - 10.1080/02678292.2018.1475686

M3 - Article

SN - 0267-8292

VL - 46

SP - 114

EP - 123

JO - LIQUID CRYSTALS

JF - LIQUID CRYSTALS

IS - 1

ER -