Mierzwa M, Floudas G, Wewerka A
Foundation for Research and Technology-Hellas (FORTH), Institute of Electronic Structure and Laser, P.O. Box 1527, 711 10 Heraklion, Crete, Greece.
Phys Rev E Stat Nonlin Soft Matter Phys. 2001 Sep;64(3 Pt 1):031703. doi: 10.1103/PhysRevE.64.031703. Epub 2001 Aug 14.
We have studied the dynamics in two side-chain liquid-crystalline derivatives of poly(norbornene diethylester) with dielectric spectroscopy within the temperature range 190-433 K and the pressure range 1-3000 bars. Optical microscopy, x-ray scattering, and differential scanning calorimetry (DSC) revealed the formation of a nematic- and a smectic-A phase, respectively, in the polymers with the shorter and longer spacers. Multiple relaxation processes exist originating from the backbone and mesogenic dipoles. In the smectic-A phase two relaxation processes exist above the DSC glass temperature (alpha and alpha(')) which merge with decreasing temperature or with increasing pressure, thus suggesting a common molecular mechanism. The faster process is the segmental (alpha) relaxation associated with the dynamic glass transition, whereas the slower process reflects mainly the side-chain dynamics within the smectic layers. Pressure was found to increase the glass temperature in the nematic and smectic phases and the dT(g)/dP was 18.7 and 16.9 K/kbar, respectively. However, the effect of pressure in inducing the isotropic-to-smectic transition is more drastic as dT(SI)/dP=26.4 K/kbar.
我们利用介电谱在190 - 433 K的温度范围和1 - 3000巴的压力范围内研究了聚（降冰片烯二乙酯）的两种侧链液晶衍生物的动力学。光学显微镜、X射线散射和差示扫描量热法（DSC）分别揭示了在具有较短和较长间隔基的聚合物中形成了向列相和近晶A相。存在源于主链和介晶偶极子的多个弛豫过程。在近晶A相中，在DSC玻璃化温度以上存在两个弛豫过程（α和α'），它们会随着温度降低或压力升高而合并，这表明存在共同的分子机制。较快的过程是与动态玻璃化转变相关的链段（α）弛豫，而较慢的过程主要反映近晶层内的侧链动力学。发现压力会提高向列相和近晶相中的玻璃化温度，dT(g)/dP分别为18.7和16.9 K/kbar。然而，压力诱导各向同性向近晶相转变的效果更为显著，因为dT(SI)/dP = 26.4 K/kbar。
