Transmission electron microscopy, liquid crystals

The morphologies of both ABA and ANA homopolymers and 73/27 ABA/ANA copol5nner prepared by thin-film polymerization show that crystallization occurs in the homopolymerization systems and the liquid crystal state remains stable in the copolymerization system (39-44), clearly indicating that the random copolymerization is an effective way to retard the crystallization. Transmission electron microscopy revealed that the microstructures of homopol5nners of ABA and ANA had more obvious lamellar texture (41-44). 

The chemical composition can be measured by traditional wet and instrumental methods of analysis. Physical surface area is measured using the N2 adsorption method at liquid nitrogen temperature (BET method). Pore size is measured by Hg porosimetry for pores with diameters larger than about 3.0 nm (30 A) or for smaller pores by N2 adsorp-tion/desorption. Active catalytic surface area is measured by selective chemisorption techniques or by x-ray diffraction (XRD) line broadening. The morphology of the carrier is viewed by electron microscopy or its crystal structure by XRD. The active component can also be measured by XRD but there are certain limitations once its particle size is smaller than about 3.5 nm (35 A). For small crystallites transmission electron microscopy (TEM) is most often used. The location of active components or poisons within the catalyst is determined by electron microprobe. Surface contamination is observed directly by x-ray photoelectron spectroscopy (XPS). 

Drugs. Farkas et al. " have used a combination of polarizing microscopy, SANS, and transmission electron microscopy to characterize the liquid crystalline phases produced by the non-ionic surfactants, Syn-peronic A7 (PEG7-C13.15), alone and in the presence of two chlorhexidine species, chlorhexidine base, and its diacetate salt. Polarizing microscopy and electron microscopy were used to examine the nature of the liquid crystals formed, while SANS was used to determine their interlayer spacing. For the SANS studies. 

The final evidence for the formation of an Abrikosov flux lattice of screw dislocations in liquid crystals was achieved by Zasadzinski et al. [39] via the visualization of the screw dislocations of (R)- and (S-)l-methylheptyl 4 -(4-n-tetradecyloxyphenylpropioloyloxy)-biphenyl-4-carboxylates using freeze-fracture transmission electron microscopy. Freeze-fracture transmission microscopy (TEM) is an essential tool for visualizing the TGBA phase at sufficient resolution in order to resolve the molecular organization. 

Surface-stabilized ferroelectric liquid crystal Splay-twist Supertwisted nematic Transmission electron microscopy Twisted nematic Thin film transistor Uniform lying helix Ultraviolet... 

Different techniques such as Fourier transform infrared (FT-IR), UV/visible spectroscopy (UV/Vis), high performance liquid chromatography (HPLC), gas chromatography (GC), transmission electron microscopy (TEM), high resolution transmission electron Microscopy (HR-TEM), and X-Ray Diffraction (XRD) have been employed for the characterization of cellulose crystals. 

When macromolecular cholesteric liquid crystals were imaged, a twisting of molecular orientation, which translated into a periodic lamellar structure in the materials, was foimd. Good agreement between afm and tern (transmission electron microscopy) was obtained in determining the widths of the lamellae. When the same polymer was processed from an isotropic solution, a homogeneous and nodular structure, lacking the periodicity of the cholesteric structure, was obtained (107). 

Transmission electron microscopy offers excellent resolution, down to the atomic level. It can provide information about molecular orientation and molecular ordering in crystals or liquid crystals, even when the ordered regions are extremely small. Combination of bright field and dark field electron microscopy with electron diffraction permits the identification of the structure of ordered regions and measurement of their orientation, perfection and size. Crystals only a few nanometers across can be detected and identified. In multiphase polymers, the... 

As discussed above, for transmission electron microscopy it is necessary to produce specimens in thin film form. In this work the following method has been adopted. A small amount of liquid crystal polymer is placed on a freshly cleaved slice of a rocksalt held at an elevated temperature (typically 10 or 20 °C above the polymer melting point TJ. The polymer is... 

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