Synthesis And Properties Of Dimesogenic Compounds Consisting Of A Cholesteryl Moiety And A 4-n-alkylcyclohexyl Phenyl Moiety

Liquid crystals are extremely important materials due to their extensive use in liquid crystal displays. The desire to achieve liquid crystal displays with optinal operating conditions, in a wide range of applications, has been the driving force of the research for new liquid crystalline materials over the last three decades.The liquid crystalline dimers possessing a cholesteryl ester unit joined to different aromatic mesogens through an alkylene spacer are currently receiving great interest in chiral dimesogens because of their chiral characteristics and strongly asymmetry. But most of the liquid crystal dimers consisting of different aromatic mesogens and a cholesteryl moiety reported in literature exhibit complicated liquid crystals behaviour or high transition temperature. Besides those dimers often exhibit high viscosity in generally.Aiming at getting low and wide phase transition temperature liquid crystals with simple thermal behaviour suitable for liquid crystal display, the first unsymmetrical dimesogenic compounds having cholesteryl and 4-trans-(4-n-alkylcyclohexyl) phenoxy groups were designed, synthesized and characterized in chapter 2. The dimers exhibit a strong alternation with n of the isotropization temperatures and the corresponding entropy changes at N*-I transition. The effect of spacer on mesophase morphology is very dependent upon the length. It was found that the dimer with longer spacer tend to exhibit N* only. The effect of terminal alkyl chain on mesophase morphology is quit dependent upon the length too. It was found that the dimers with longer terminal alkyl chain tend to exhibit SmA besides N~*.Our main findings are:1, compared with published dimesogens, the mesophases observed in this paper are simple.2, those dimers have significant features of good thermal stability.3, compared with other dimesogens, the dimesogens synthesized in our present...