Browsing by Author "Foo, K. -L."

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Mesomorphic behaviors of a series of heterocyclic benzothiazole-imine-ester-based liquid crystals
(2019-01-01)
Foo, K. -L.
;
Ha, S. -T.
;
Yeap, G. -Y.
;
Lin, H. -C.
;
材料科學與工程學系
A series of new calamitic liquid crystals, 2-[4-(4-alkoxybenzoyloxy) benzylidenamino]benzothiazoles comprising a heterocyclic (benzothiazole) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were prepared and characterized. This series comprises eight members wherein the members vary by the length of alkoxy chain (CnH2n+1O-, where n = 4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in conformity with the expected structure. Their thermotropic behaviors were studied by using differential scanning calorimetry, optical polarizing microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first member of the series (n = 4). As the alkoxy chain increased to n = 6, 8, 10, 12, 14, the nematic phase appeared together with an additional SmA phase. When moving from n = 16 until the highest member (n = 18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA).
Synthesis and mesomorphic behaviors of a series of heterocyclic pyridine-imine-ester based liquid crystals
(2019-10-03)
Foo, K. -L.
;
Ha, S. -T.
;
Yeap, G. -Y.
;
Lin, H. -C.
;
材料科學與工程學系
A series of new calamitic liquid crystals, 4-{[(5-methylpyridin-2-yl)imino]methyl}phenyl 4-alkoxybenzoates were synthesized. This series consists of nine members wherein they are differed by the length of alkoxy chain. Spectral analysis results were in accordance with the expected structure. Their thermotropic behaviors were analyzed with Differential Scanning Calorimetry (DSC), Polarizing Optical Microscopy (POM) and powder X-ray diffraction techniques. First member with the shortest alkoxy chain (n = 2) is a non-mesogen. As the alkoxy chain increased to n = 4, the monotropic nematic phase appeared. An enantiotropic mesophase (nematic) was observed for the following three members (n = 6, 8, 10). As the alkoxy chain increased to n = 12, enantiotropic nematic phase exhibited together with monotropic smectic A (SmA) phase. As the alkoxy chain continuously increased to n = 14 and 16, enantiotropic phases were observed for both N and SmA. When moving to n = 18, the nematic phase disappeared and this compound only exhibited a single mesophase (SmA).