| Summary: | 碩士 === 大同大學 === 化學工程研究所 === 91 === ABSTRACT
The primary of this research work was an attempt to elucidate the structure-property correlation in the achiral smectic liquid crystals. A homologous series of achiral materials derive from diethylaminoalkanols has been successfully synthesized and the structure-property relationship investigated. The target compounds were modified independently by the (i) nonchiral preipheral length chain, (ii) swallow-tailed group and (iii) core of the molecules of the achiral molecules for the study.
Achiral swallow-tailed materials, I(m, p, q; m=8~12, p=1, q=2), displayed enantiotropic mesophases of the SmA and SmCalt phases. The SmCalt phase was confirmed by the first order characterization of SmA- SmCalt transition in the DSC thermograms and farther identified by the schlieren texture showing two-brush and four-brush singularities. Temperature range of the SmA phases decreased as the number of methylene units between core and swallow-tail group of the molecules increased. The thermal stability of SmCalt phase for all materials is nearly the same.
Achiral swallow-tailed materials, II(m, p, q; m=8~12, p=1, q=2), displayed enantiotropic mesophases of the SmA and SmCalt phases. The SmCalt phase was also confirmed by the first order characterization of SmA-SmCalt transition in the DSC thermograms and farther identified by the schlieren texture showing two-brush and four-brush singularities. The thermal stability of SmA phase is decreased significantly as the number of methylene units between core and swallow-tail group of the molecules increased. The thermal stability of SmCalt phase for II (m, p, q; m=8, p=1, q=2) and II (m, p, q; m=9, p=1, q=2) are relatively larger while the rest of materials are nearly the same.
Achiral swallow-tailed materials, III(m, p, q; m=10, p=1, q=2), displayed varieties of enantiotropic mesophases by the variations of swallow-tail groups. Compound III(a) displayed enantiotropic mesophases of the N and SmA phases. Compound III(b) displayed enantiotropic mesophases of the SmA and SmC phases. Compound III(c) displayed enantiotropic mesophases of the SmA and SmCalt phases and has lower melting point. Compound III(d) displayed enantiotropic mesophases of the SmA and SmCalt phases and has wider temperature range of SmCalt phase and lower melting point than III(c).
Achiral swallow-tailed materials, IV(m, p, q; m=10, p=2, q=1), displayed enantiotropic mesophases of the SmA and SmCalt phases. The SmCalt phase was confirmed by the first order characterization of SmA-SmCalt transition in the DSC thermograms and farther identified by the schlieren texture showing two-brush and four-brush singularities. Compound IV(b) has wider temperature range of SmCalt phase and lower melting point than IV(a).
In conclusion, the results indicated that the achiral swallow-tailed materials derived from diethylaminoalkanols are favorable for the formation of the alternating phase. Compound IV(b) displays the widest temperature range of SmCalt phase and the lowest melting point.
According to the energy-minimized molecular model simulation, the achiral swallow-tailed liquid crystals derived from diethylaminoalkanols are favorable of formation of SmCalt phase.
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