Marbled texture

Note On observing a sample with a marbled texture between crossed polarizers, the interference colour is essentially uniform within each individual area, indicating an essentially homogeneous region. 

Nematic marbled texture consists of several areas with different molecular orientation. On observing the preparation between... 

For (lb), having the long flexible spacer of six methylene units a normal nematic phase is observed displaying the typical vi/ell known nematic textures under the polarizing microscope. Marbled textures as well as Schlieren textures can be seen, and they exhibit the same types of defects as ordinary l.-lc s. Conoscopic observations clearly prove the optically uniaxial positive character. The absolute value of the birefringence An as well as the temperature dependence of An correspond to chemically similar l.-lc s ... 

Other textures associated with nematic LCs include the thread-like texture and the marbled texture, both of which are caused by a strong interaction of the thin nematic layer with the surrounding walls [1,3,10]. 

Nematic phases typically show a schlieren texture between crossed polarizers if the director is oriented perpendicular to the viewing direction. One feature of the schlieren texture is the occurrence of topological point defects. At these point defects either two or four dark brushes meet. The corresponding defects are denoted as 1/2 or 1, respectively. Further characteristic textures of the nematic phase are the thread-like texture, which exhibits n disclinations parallel to the substrate, and the marble texture, in which areas of differing uniform director orientations occur. 

Mostly thermotropic polyesters show a nematic phase with a typical appearance that is called a marbled texture, a Schlieren texture, a threaded texture, or, a nematic droplets depending on the thickness and temperature of the polyester. Only in a few cases, they exhibit low-order smectic phases [100], which are identified through the observations of fan-shaped and broken fan textures in their LC phases. No report of higher-order smectic phases has been observed in this class of pol)nners. It is worth mentioning that nematic texture can simply be frozen into a glassy state in the case where there is no interference from the crystallization process. An intriguing property of an LC polyester is its biphase structure over... 

Identification of the nematic mesophase through polarized light microscopy is easier than that of the smectic mesophase, because specific defects take a linear form. The nematic mesophase is characterized by a large number of textures Schilieren texture is one of the most common nematic textures with defect centers with two arms, nematic droplets often occur from the isotropic liquid in the form of drops, string texture consists of a disclination type - line and appears as thin lines, and marble texture consists of several zones with different orientations of the director, inducing different color interferences [5]. 

The similarity to low-molecular-weight nematics consists of the fact that nematic polymers can form schlieren and marble textures characteristic of nematics the enthalpy of the transition from the LC state to an isotropic melt is also close to the analogous values for low-molecular-weight nematics and usually does not exceed 6-8 J/g. 

In most cases the textures exhibited by polymers in the nematic state are similar to those of LMMLCs. The Schlieren, threaded and marbled textures are the ones most often cited in the literature. Examples of typical polymeric textures are shown in Figs 2.15 and 2.16. ... 

Nematic marbled texture consists of several areas with different molecular orientation. On observing the preparation between crossed polarizers, one can note that the interference colour is nearly constant within the individual areas, indicating quasi-homogeneous regions. 

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