Effect of Molecular Structure on Mesomorphism. 18.1 Twin Dimers Having Methylene, Ethylene Oxide and Siloxane Spacers
Document Type
Article
Publication Date
1-1-1987
Department
Chemistry and Biochemistry
School
Mathematics and Natural Sciences
Abstract
Six Twin dimeric compounds having two rigid cores connected by a central spacer group are described. Two types of rigid units, 4-pentyloxyphenyl cinnamates and 4-cyano-4-oxybiphenyl, were employed. The spacer groups were pentamethylene (PM), diethylene oxide (EO) and disiloxane (DS). For each rigid core the nematic-isotropic temperature followed the order PM > EO > DS. Investigation of the ΔH and ΔS parameters for the nematic-isotropic (clearing) transition revealed that for these compounds the clearing transition was driven by ΔS. The EO mesogens have larger ΔS values than for the PM mesogens, which result in lowered clearing temperatures due to relatively constant ΔH values. The conformational preference for gauche isomers in the spacer of the EO compounds is seen as conducive to proper orientational alignment of the rigid cores in the nematic phase, better so than for the PM and DS spacers.
Publication Title
Molecular Crystals and Liquid Crystals
Volume
149
Issue
1
First Page
185
Last Page
193
Recommended Citation
Creed, D.,
Gross, J. R.,
Sullivan, S. L.,
Griffin, A. C.,
Hoyle, C. E.
(1987). Effect of Molecular Structure on Mesomorphism. 18.1 Twin Dimers Having Methylene, Ethylene Oxide and Siloxane Spacers. Molecular Crystals and Liquid Crystals, 149(1), 185-193.
Available at: https://aquila.usm.edu/fac_pubs/21364