Optical microscopy condenser

The DBSA-system is also applicable for the dithioacetalization of aldehdyes and ketones with 1,2-ethanedithiol to give the corresponding dithioacetals (Scheme 5.4, d). Increasing the reaction temperature decreases the yield of the products. Interestingly, increases in the concentration of the surfactant also decrease the yield of products formed, while shortening the alkyl chain of the surfactant abolishes its catalytic activity. Optical microscopy shows the formation of micelles, which are proposed to form hydrophobic environments and decrease the effective concentration of water and facilitate the dehydrative condensation reactions. 

A complete characterization of liquid crystalline polymers should include at least two aspects the characterization of the molecular structure and that of the condensed state structure. Since the first characterization is nothing more than what is practiced for non-liquid-crystalline polymers, we will restrict the discussion to only a short introduction of methods mostly used in the characterization of the presence and the main types of polymeric liquid crystal phases. The methods include the mostly used polarizing optical microscopy (POM, Section 4.1), differential scanning calorimetry (DSC, Section 4.2) and X-ray diffraction (Section 4.3). The less frequently used methods such as miscibility studies, infrared spectroscopy and NMR spectroscopy will also be discussed briefly (Section 4.4). 

In conventional optical microscopy a beam of light is focused on to a specimen by a condenser lens and hght transmitted or reflected by the sample is collected by the objective lens (Fig. 12.28). The magnified image of the specimen... 

Standard optical microscopic techniques are limited to optically thin specimens. An increased fluorophore density, a high refractive index contrast (which is a possible scenario in polymer blends) and attenuation due to the long optical path may each increase the optical density of the specimen, and this will render a sample extremely difficult (perhaps even impossible) to image using standard techniques [15]. In order to address this issue, confocal optical microscopy was developed, which combines the optical components of typical microscopy and scattering devices [16]. Although this technique is widely used in the biological sciences, the condensed matter physics community has recently started to use the technique to study the stmcture and dynamics of complex fluids. 

X-ray, electron scattering and thermal analysis remain the main tools in analyzing liquid crystalline order in condensed polymeric materials. The effectiveness of optical microscopy and of the compatibility rules formulated by Sackmann and Demus a decade ago and widely used in identification of mesophases formed by low molecular compounds (41, 42) is questionable in the case of... 

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