Thermochromism of a liquid crystalline dialkoxy substituted poly(1,4-phenylene-1,3,4-oxadiazol-2,5-diyl)
作者:Andreas F. Thünemann、Silvia Janietz、Sonja Anlauf、Armin Wedel
DOI:10.1039/b005757f
日期:——
The thermotropic liquid crystalline behavior of poly[2′,5′-bis(hexadecyloxy)-1,4-phenylene-1,3,4-oxadiazol-2,5-diyl] C16pod was investigated using differential scanning calorimetry, small-
and wide-angle X-ray scattering techniques. An order–order transition
was found at about 120 °C, which was attributed to the transition
from a smectic H phase at a low temperature to a smectic A phase at a high
temperature. The repeat unit of the smectic H phase is d = 3.70 nm
which is composed of a polymer-rich layer (d1 = 1.70 nm)
and an alkyl chain rich layer (d2 = 2.00 nm).
For the smectic A phase we calculated d = 3.85 nm, d1 = 1.75 nm
and d2 = 2.10 nm. The lamellae of the
smectic A phase are assumed to show undulations with a periodicity of 6.3 nm.
By contrast, the smectic H phase has no periodic undulations. The C16pod
changes its color from yellow–green at 25 °C to blue at 130 °C.
UV-vis and fluorescence spectroscopy were used for a quantitative determination
of the thermochromicity of C16pod. It was found that the optical
properties change continuously within a temperature range of 25 to 140 °C.
Even at the order–order transition the UV-vis and fluorescence intensities
change continuously. It was therefore concluded that the effective conjugation
length of the C16pod reduces continuously with increasing temperature.
The order–order transition is caused predominantly by the melting of
the side-chains.
利用差示扫描量热法、小角和广角 X 射线散射技术研究了聚[2′,5′-双(十六烷氧基)-1,4-亚苯基-1,3,4-恶二唑-2,5-二基] C16pod 的热致液晶行为。在大约 120 °C 时发现了一个阶-阶转变,这是由低温下的共晶 H 相向高温下的共晶 A 相转变所致。Smectic H 相的重复单元为 d = 3.70 nm,由富含聚合物层(d1 = 1.70 nm)和富含烷基链层(d2 = 2.00 nm)组成。 对于 Smectic A 相,我们计算出 d = 3.85 nm,d1 = 1.75 nm,d2 = 2.10 nm。我们假定 Smectic A 相的薄片呈现出周期为 6.3 nm 的起伏。 相比之下,Smectic H 相没有周期性起伏。C16pod 的颜色从 25 °C 时的黄绿色变为 130 °C 时的蓝色。紫外-可见光谱和荧光光谱用于定量测定 C16pod 的热变色性。结果发现,在 25 至 140 ℃ 的温度范围内,其光学特性不断发生变化。阶跃转变主要是由侧链熔化引起的。