Anomalies of periodicity in some liquid crystalline cyano derivatives
Anomalies of periodicity in some liquid crystalline cyano derivatives
复制标题
一些液晶氰基衍生物的周期性异常
DOI：
--
复制
发表时间：
1981
期刊：
影响因子：
--
通讯作者：
G. Sigaud
中科院分区：
文献类型：
--
作者：
F. Hardouin;A. Levelut;G. Sigaud
通过X射线衍射实验，观察到了一些端基为氰基的液晶材料的近晶相和非晶相的质量密度涨落的异常模式。特别是，第一次，我们给出了一个纯化合物（DB 7）的SA-SA转变的证据：在高温SA 1相的波长等于1.6分子长度的长程密度波与一个约一个分子长度的短程波长共存。在低温下，发生向SA 2相的转变，并且我们看到两个尖锐的布拉格斑点，其对应于通过两个分子长度周期性的调制的两个第一衍射级。此外，另一种氰基衍生物，它同时表现出重入的近晶A相和重入的近晶A相揭示了两种调制在这些阶段的同时存在和竞争。但是，折返相位的出现似乎与两个特征波长的相称或不相称锁定无关。
Unusual modes for mass density fluctuations are observed by X-ray experiments in nematic and smectic phases of some liquid crystalline materials with cyano end group. In particular, for the first time, we give evidence for a S A-SA transition in a pure compound (DB7) : in the high temperature SA1 phase a long-range density wave with a wavelength equal to 1.6 molecular length coexists with a short-range wavelength of about one molecular length. At low temperature a transition towards an SA2 phase occurs and we see two sharp Bragg spots which correspond to the two first-orders of diffraction by a modulation of two molecular length periodicity. Further another cyano derivative which exhibits both reentrant nematic and reentrant smectic A phases reveals the simultaneous existence and the competition of two modulations in these phases. But the occurrence of a reentrant phase does not seem to be connected to a commensurate or incommensurate lock-in of the two characteristic wavelengths.