Storz Rebekka, Komp Ansgar, Hoffmann Anke, Finkelmann Heino
Institut für Makromolekulare Chemie, Stefan-Meier-Str. 31, 79104 Freiburg, Germany.
Macromol Rapid Commun. 2009 Apr 20;30(8):615-21. doi: 10.1002/marc.200800793. Epub 2009 Mar 9.
(2) H NMR investigations on the biaxial phase behavior of smectic-A liquid crystalline side-chain elastomers are presented. Biaxiality parameters were determined by measuring the quadrupolar splitting of two spin probes, namely benzene-d(6) and hexamethylbenzene-d(18) , at various angles between the principal director and the external magnetic field: while for a uniaxial sample the angular dependence can be described by the second Legendre polynomial, an additional asymmetric term needs to be included to fit the data of the two investigated biaxial systems. Two elastomers synthesized from mesogens that differ in the molecular geometry in order to study the molecular origin of biaxiality were compared. Biaxiality is observed for both elastomers when approaching the glass transition, suggesting that the network dynamics dominate the formation of the biaxial phase.
本文介绍了对近晶-A型液晶侧链弹性体双轴相行为的¹H NMR研究。通过测量两个自旋探针，即苯-d(6)和六甲基苯-d(18)，在主指向矢与外磁场之间不同角度下的四极分裂来确定双轴性参数：对于单轴样品，角度依赖性可用二阶勒让德多项式描述，而对于两个被研究的双轴体系的数据拟合，需要包含一个额外的不对称项。比较了由分子几何结构不同的介晶体制备的两种弹性体，以研究双轴性的分子起源。当接近玻璃化转变时，两种弹性体均观察到双轴性，这表明网络动力学主导了双轴相的形成。
