Browsing by Author "Lee, Siew Ling"

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Synthesis and mesomorphic evaluation of new calamitic liquid crystals containing benzothiazole core
(2011-05-01)
Koh, Teck Ming
;
Ha, Sie Tiong
;
Lee, Teck Leong
;
Lee, Siew Ling
;
Yeap, Guan Yeow
The design and synthesis of new calamitic benzothiazole-based liquid crystals, 2[4-(4-alkyloxybenzoyloxy)-phenyl]benzothiazoles are presented. The target compound was characterized using spectroscopic techniques, such as FT-IR, NMR ((1)H and (13)C), microanalysis and EI-MS. The liquid crystalline behaviours of these compounds were thoroughly examined by differential scanning calorimetry and polarizing optical microscope techniques. These materials exhibited enantiotropic nematic phase with high thermal stability (> 168 degrees C). Smectic A phase starts to emerge as monotropic (metastable) phase from C10 member and changes into enantiotropic (stable) phase from C12 and persists up to C16 members. (C) 2010 Sie Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Synthesis and mesomorphic properties of Schiff base esters possessing terminal chloro substituent
(2010-06-01)
Ha, Sie Tiong
;
Ong, Lay Khoon
;
Lee, Siew Ling
;
Lin, Hong Cheu
;
Win, Yip Foo
A homologous series of Schiff base esters, 4-chlorobenzylidene-4'-n-alkanoyloxyanilines, containing even number of carbons at the end groups of the molecules (C(n-1)H(2n-1)COO-, n = 4, 6, 8, 10, 12, 14, 16) were synthesized. The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). It was found that the end groups of the molecules had an effect on the mesomorphic properties. n-Butanoyloxy was found non-mesogenic, whilst n-hexanoyloxy exhibited monotropic smectic phase. The higher members in this homologous series were enantiotropic smectogens. (C) 2010 Sie Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.