Yeap Guan Yeow - Academia.edu (original) (raw)
Papers by Yeap Guan Yeow
New Journal of Chemistry, 2020
A new series of tri-substituted phenyl derivatives containing an aromatic imine unit and biphenyl... more A new series of tri-substituted phenyl derivatives containing an aromatic imine unit and biphenyl ester possessing various numbers of carbon atoms at the terminal alkoxy chain, OCnH2n+1 (n = 7–12), along with a lateral o-ethoxy substituent have been successfully prepared and characterised by CHN microanalysis along with spectroscopic techniques (FTIR, 1H- and 13C-NMR). The texture observation under polarized light revealed that all the soft condensed materials exhibited an enantiotropic nematic (N) phase. The current studies have shown that the mesomorphic behaviour is greatly influenced by the length of the alkoxy chains wherein the thermal stability of a tri-substituted phenyl derivative will decrease if the terminal alkoxy chain is increased from n = 7 to 12. For the first time, these materials which do not possess any magnetic species in their structure, demonstrate magnetic interaction through naked eye observation as well as quantitative measurement using a SQUID magnetometer.
Journal of Molecular Liquids, 2016
A new homologous series of mesogens containing 6-amino-1,3-dimethyluracil moiety have been synthe... more A new homologous series of mesogens containing 6-amino-1,3-dimethyluracil moiety have been synthesized. The structures of the compounds were characterised by elemental analysis, FT-IR, 1H and 13C NMR spectroscopic techniques. Their mesomorphic properties were studied by polarising optical microscopy attached to a heating stage. Microscopy data were supported with transition temperatures and enthalpy change values obtained from the differential scanning calorimetry analysis. The studies have shown that the mesomorphic properties of the compounds are dependent on the lengths of alkoxy-spacers. Compounds 4a-f with a shorter alkoxy-spacer chain (n = 6) exhibited smectic A phase, while compounds 4g-r with a alkoxy-spacer chain (n = 8 or 10) displayed nematic phase.
Advanced Materials Research, 2014
In the field of liquid crystals, blue phases (BPs) are one of the most unique and interesting sub... more In the field of liquid crystals, blue phases (BPs) are one of the most unique and interesting sub-phases. Blue-phase liquid crystal holds the potential to become next-generation display and photonics device because of its sub-millisecond gray-to-gray response time, alignment-layer-free process, optically isotropic dark state, and cell gap insensitivity. The BPLC is a highly chiral liquid crystal system possessing crystal like unit cell structure and exist over a small temperature range (0.5-2 °C) between isotropic and chiral nematic (N*) thermotropic phase. The narrow phase range has been an intrinsic problem for blue phase, and a useful strategy of widening the phase is by adding polymer to form a polymer stabilised blue phase liquid crystal. In this paper, we demonstrate polymer stabilization using two different cases: a room temperature mixture containing E8, PE-5CNF and CPP-3FF, and a high temperature mixture using a single molecule blue phase liquid crystal material, TCB5. Comp...
American Journal of Applied Sciences, 2010
Problem statement: Numerous studies have been conducted on the Schiff base's alkyl and alkyloxy p... more Problem statement: Numerous studies have been conducted on the Schiff base's alkyl and alkyloxy possessing aromatic core. However, the thermo tropic properties of Schiff base's ester (or alkanoyloxy) with pyridine core was rare studied. Approach: To study spectral, thermal and optical behaviors of Schiff base ester possessing heterocyclic (pyridine) terminal core. A series of 4-[(pyridin-3-ylmethylene) amino] phenylalkanoates were prepared and all the members are differed by the length of alkanoyloxy chain, C n-1 H 2n-1 COO, where n = 12, 14, 16 and 18. The thermal and optical characteristics were studied using differential scanning calorimetry and polarizing optical microscopy. Results: DSC studies showed that all of the title compounds exhibited direct isotropization and recrystallization during heating and cooling cycles, respectively. Under polarizing optical microscope, crystal phase texture was observed to change to dark region isotropic without displaying any liquid crystal phase. Conclusion: The presence of terminal pyridine core suppressed the formation of mesosphere in the compounds studied.
![Research paper thumbnail of 4-[(Pyridin3-ylmethylene)amino]phenyltetradecanoate](https://attachments.academia-assets.com/73564306/thumbnails/1.jpg)
](Molbank, 2009
A new Schiff base 4-[(pyridin-3-ylmethylene)amino]phenyltetradecanoate was synthesized and its IR... more A new Schiff base 4-[(pyridin-3-ylmethylene)amino]phenyltetradecanoate was synthesized and its IR, 1 H NMR, 13 C NMR and MS spectroscopic data are presented.
New Journal of Chemistry, 2020
A new series of tri-substituted phenyl derivatives containing an aromatic imine unit and biphenyl... more A new series of tri-substituted phenyl derivatives containing an aromatic imine unit and biphenyl ester possessing various numbers of carbon atoms at the terminal alkoxy chain, OCnH2n+1 (n = 7–12), along with a lateral o-ethoxy substituent have been successfully prepared and characterised by CHN microanalysis along with spectroscopic techniques (FTIR, 1H- and 13C-NMR). The texture observation under polarized light revealed that all the soft condensed materials exhibited an enantiotropic nematic (N) phase. The current studies have shown that the mesomorphic behaviour is greatly influenced by the length of the alkoxy chains wherein the thermal stability of a tri-substituted phenyl derivative will decrease if the terminal alkoxy chain is increased from n = 7 to 12. For the first time, these materials which do not possess any magnetic species in their structure, demonstrate magnetic interaction through naked eye observation as well as quantitative measurement using a SQUID magnetometer.
Journal of Molecular Liquids, 2016
A new homologous series of mesogens containing 6-amino-1,3-dimethyluracil moiety have been synthe... more A new homologous series of mesogens containing 6-amino-1,3-dimethyluracil moiety have been synthesized. The structures of the compounds were characterised by elemental analysis, FT-IR, 1H and 13C NMR spectroscopic techniques. Their mesomorphic properties were studied by polarising optical microscopy attached to a heating stage. Microscopy data were supported with transition temperatures and enthalpy change values obtained from the differential scanning calorimetry analysis. The studies have shown that the mesomorphic properties of the compounds are dependent on the lengths of alkoxy-spacers. Compounds 4a-f with a shorter alkoxy-spacer chain (n = 6) exhibited smectic A phase, while compounds 4g-r with a alkoxy-spacer chain (n = 8 or 10) displayed nematic phase.
Advanced Materials Research, 2014
In the field of liquid crystals, blue phases (BPs) are one of the most unique and interesting sub... more In the field of liquid crystals, blue phases (BPs) are one of the most unique and interesting sub-phases. Blue-phase liquid crystal holds the potential to become next-generation display and photonics device because of its sub-millisecond gray-to-gray response time, alignment-layer-free process, optically isotropic dark state, and cell gap insensitivity. The BPLC is a highly chiral liquid crystal system possessing crystal like unit cell structure and exist over a small temperature range (0.5-2 °C) between isotropic and chiral nematic (N*) thermotropic phase. The narrow phase range has been an intrinsic problem for blue phase, and a useful strategy of widening the phase is by adding polymer to form a polymer stabilised blue phase liquid crystal. In this paper, we demonstrate polymer stabilization using two different cases: a room temperature mixture containing E8, PE-5CNF and CPP-3FF, and a high temperature mixture using a single molecule blue phase liquid crystal material, TCB5. Comp...
American Journal of Applied Sciences, 2010
Problem statement: Numerous studies have been conducted on the Schiff base's alkyl and alkyloxy p... more Problem statement: Numerous studies have been conducted on the Schiff base's alkyl and alkyloxy possessing aromatic core. However, the thermo tropic properties of Schiff base's ester (or alkanoyloxy) with pyridine core was rare studied. Approach: To study spectral, thermal and optical behaviors of Schiff base ester possessing heterocyclic (pyridine) terminal core. A series of 4-[(pyridin-3-ylmethylene) amino] phenylalkanoates were prepared and all the members are differed by the length of alkanoyloxy chain, C n-1 H 2n-1 COO, where n = 12, 14, 16 and 18. The thermal and optical characteristics were studied using differential scanning calorimetry and polarizing optical microscopy. Results: DSC studies showed that all of the title compounds exhibited direct isotropization and recrystallization during heating and cooling cycles, respectively. Under polarizing optical microscope, crystal phase texture was observed to change to dark region isotropic without displaying any liquid crystal phase. Conclusion: The presence of terminal pyridine core suppressed the formation of mesosphere in the compounds studied.
Molbank, 2009
A new Schiff base 4-[(pyridin-3-ylmethylene)amino]phenyltetradecanoate was synthesized and its IR... more A new Schiff base 4-[(pyridin-3-ylmethylene)amino]phenyltetradecanoate was synthesized and its IR, 1 H NMR, 13 C NMR and MS spectroscopic data are presented.