Synthesis and Invistigation of Ntb Phase Properties in Dimeric Materials

Abstract

Investigation of the Ntb phase in mixtures of dimeric liquid crystal DTC5C9 with DTC5C7 and DTC5C9CB is hereby reported. The gels of liquid crystal mixtures of CBC9CB and CW539 in different ratio were also investigated using 12-Hydroxyoctadecanoic acid as the gelling agent. It was observed that all the binary system showed transition from conventional nematic phase to the Ntb phase at relatively similar temperature range and the isotropisation temperature for all sample mixtures looks constant. On the other hand, the melting points of pure DTC5C7 (98°C) and DTC5C9 (95°C) are higher than the values for the binary mixtures. On heating in general, there was gradual reduction in the transition temperature from melting to Ntb, Ntb–N transition, and finally, N–Iso transition. Pure DTC5C9CB melted at 69°C to the low-temperature nematic phase, Ntb, and was maintained for 47°C, transited to conventional nematic phase, N, and finally isotropic at 150°C. On heating in general, there was gradual reduction in the transition temperature from melting to Ntb, Ntb–N transition, and finally, N–Iso transition. Pure DTC5C9CB melted at 69°C to the lowtemperature nematic phase, Ntb, and was maintained for 47°C, transited to conventional nematic phase, N, and finally isotropic at 150°C. The investigation of different liquid crystalline mixture materials which include CBC9CB with CW539, CW538, 5CB and ZA245 showed that at least 80% of the mesogen is required to exhibit Ntb phase. Further work into gels of liquid crystal mixtures of CBC9CB and CW539 in different ratios, using 12-Hydroxyoctadecanoic acid as gelling agent also showed interesting textures and low transitions temperatures values. As the CW539 increases in the mixture, there is increase in the stability temperature of the high-temperature nematic phase by extra 10% for samples with the emergence of the low-temperature nematic phase, Ntb, at the addition of 40% CW539, with stability temperature of about 23°C. There was an increase in the stability temperature range for the Ntb phase until it maintains about 30°C from the addition of 70% CW539. Furthermore, mesogenic polymer was synthesized by reacting the terminal alkene of mesogen with the silane end of the polymethylhydrosiloxane by hydrosilylation reaction. The polymer melted into nematic phase at 35.9°C with an enthalpy change of 2.5 Jg-1 before turning isotropic at 86.1°C and crystallizes at 39.7°C (-18.1 Jg-1). The interesting nematic marble texture was observed on POM. The details of the investigations are contained in this writeup.