Two new series of racemic dimeric liquid crystals containing terminal
alkyl chains with methyl branches are presented; in one the dimers are
symmetric and in the other they are non-symmetric. Comparisons are made
with the structurally isomeric series with no methyl branches in their
terminal alkyl chains. The stability and clearing temperatures of the
liquid crystal phases are markedly reduced for the dimers with methyl
branches, particularly for the symmetric dimers. Chiral analogues of both
series were also examined. The liquid crystal behaviour of the
non-symmetric dimers is of particular interest. Four homologues were
studied with the number of methylene units in the spacer ranging from six
to nine. An odd–even effect was observed for the chiral properties
of these materials. Blue phase I behaviour was exhibited by the heptane
and nonane homologues but not by the even membered hexane and octane
members of the series.
本文介绍了两个新的外消旋二聚液晶系列,其中一个系列中的二聚物是对称的,另一个系列中的二聚物是不对称的。并与末端烷基链中没有甲基分支的结构异构系列进行了比较。有甲基支链的二聚体,尤其是对称二聚体,液晶相的稳定性和清澈温度明显降低。我们还研究了这两个系列的手性类似物。非对称二聚体的液晶行为尤其引人关注。我们研究了四种同系物,其间隔中亚甲基单位的数量从六个到九个不等。观察到这些材料的手性具有奇偶效应。该系列中的
庚烷和
壬烷同系物表现出蓝色 I 相行为,而偶数成员的己烷和
辛烷则没有。