Nematic marbled texture

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

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. 

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. ... 

When an isotropic texture appears on cooling from an isotropic melt, it is formed from the coalescence of droplets that separate from the liquid. This mechanism is indicative of a nematic phase, and one of three possible characteristic textures may result, depending on the way the droplets form larger domains. These are the Schlieren, the threaded, or the marbled nematic textures. An example of Schlieren texture is shown in Figure II. 12. 

In addition to end-on attachment, there is also side-on attachment of rod-like molecules onto GNPs. Through laterally substituted thiol, the rod-like nematic LC molecule 10 containing a lateral alkyl thiol was linked to GNPs together with some other /2-alkane thiols forming a mixed monolayer (Scheme 4.3), which had two components in nearly equal proportions (ca. 1 1) on GNP surface (Fig. 4.6). Both the hexane- and dodecanethiol coated hybrids GNPs exhibited nematic LC behavior which displayed typical marbled or Schlieren textures (Fig. 4.7) [55]. 

As responding to the reaction (2), the LC ceil exhibits three disorete textures of the nematic LC phase (marbled parallel (PI) on A, H for B, and then sdilieren parallel (P2) for C, Figure 4). The result clearly indicates that the H alignment is highly sensitive to the amount of the monomeric trans-Az on the surface. To promote the H alignment, highly interactive monomeric trans-Az should be required. 

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