Microscope/microscopy polarising

Most of the techniques employed in fibre analysis are nondestructive tests to determine whether the fibre is natural (obtained from animal, plant, or mineral) or synthetic (wholly manufactured from chemicals or regenerated from natural fibres) and the fibre type (e.g., determining if the fibre is wool, cotton, nylon, polyester, etc.). Whether any chemical treatments have been carried out (such as bleaching or the use of delustrants) is noted and the colour is also determined. Many of the techniques commonly used in these analyses include low- and high-power microscopes, Fourier transform infrared (FTIR) microscopy, polarising Ught microscopy, fluorescence microscopy, and microspectrophotometry (MSP). 

M. H. Butler, Polarised Eight Microscopy in the Conservation of Paintings, centennial volume. State Microscopical Society of Hlinois, Chicago, pp. 1—17, 1970. 

The most common and easily applicable method of characterising liquid crystalline mesophases is polarisation microscopy. In this method, thin samples of the surfactant solution are viewed under a microscope between crossed polarisation filters. Due to optical anisotropy of liquid crystals they are birefringent. Hence, they give rise to a brightness in the microscope and show patterns that are very characteristic for the specific phases examples are shown in Figure 3.17. 

The apparatus used for IR microscopy is a Fourier-transform infrared (FTIR) spectrometer coupled on-line with an optical microscope. The microscope serves to observe the sample in white light at significant magnification for the purpose of determining its morphology, as well as to select the area for analysis. The spectrometer, on the other hand, enables study of the sample by transmission or reflection measurement for the purpose of determining the chemical composition. It also provides information about the microstructure and optical properties (orientation) of the sample. It is possible to apply polarised light both in the observation of the sample and in spectrometric measurements. 

When a bicontinuous cubic lipid-water phase is mechanically fragmented in the presence of a liposomal dispersion or of certain micellar solutions e.g. bile salt solution), a dispersion can be formed with high kinetic stability. In the polarising microscope it is sometimes possible to see an outer birefringent layer with radial symmetry (showing an extinction cross like that exhibited by a liposome). However, the core of these structures is isotropic. Such dispersions are formed in ternary systems, in a region where the cubic phase coexists in equilibrium with water and the L(x phase. The dispersion is due to a localisation of the La phase outside cubic particles. The structure has been confirmed by electron microscopy by Landh and Buchheim [15], and is shown in Fig. 5.4. It is natural to term these novel structures "cubosomes". They are an example of supra self-assembly. 

Polarised l t microscopy, in which the sample is illuminated with Hnearly or circularly polarised light, either in a reflection or transmission mode. One polarising element, located below the stage of the microscope, converts the illumination to polarised light, while a second polariser is located between the objective and the ocular and is used to detect polarised light. Various characteristics of the specimen can be determined, including anisotropy, polarisation colours, birefringence, and polymorphism. 

The analysis of materials that possibly contain asbestos can be carried out by various methods, however the dispersion staining microscopic technique is considered to be a quick, reliable and cost-effective method that is used by the majority of laboratories that routinely carry out this type of work. This method should be in accordance with MDHS 77 (1994), which is published by the UK Health and Safety Executive and forms part of the series of the methods for the determination of hazardous substances, titled Asbestos in Bulk Materials -sampling and identification by polarised light microscopy (PLM). 

It is easy to observe spherulite growth in a thin film of low molecular weight polyethylene oxide, melt between a microscope slide and a cover slip, using polarised light microscopy. The spherulites grow as discs once their diameter exceeds the film thickness of about 0.1 mm. The discs have a radiating fibrous appearance and a Maltese cross pattern with arms parallel to the crossed polarising filters below and above the specimen (Fig. 3.24b). However, these two-dimensional spherulites are a rarity in nearly all cases the spherulites are three-dimensional with polyhedral boundaries. 

Low- and high-powered microscopes are used to examine the morphological features of the fibres and the initial determination of whether the fibre is natural or man-made. FTIR microscopy can be used on a synthetic fibre to provide information in relation to the functional groups present this can be used to pinpoint which synthetic fibre it is. Polarising light microscopy is used with synthetic fibres plane-polarised Ught interacts with the fibres in order to provide refractive index values (many of these fibres have two refractive indices due to the chemical structure of the fibre and are said to be birefringent). This helps in the identification of the synthetic fibre. 

Optical microscopy was performed with a Reichert Thermopan polarising microscope equipped with a Leitz camera. The thermal studies were conducted with a Dupont 910 Differential Scanning Calorimeter. 

Polarised confocal Raman microscopy was used to measure molecular orientation in uniaxially drawn PETP films, prepared with draw ratios from 1 to 3.5. The orientation of both polarised Raman microscopy and polarised attenuated total reflection IR spectroscopy. Crystallinity profiles were measured through the thickness of the film samples and compared with the orientation gradients existing in the films. This procedure was to determine whether the intuitive assumption that orientation and crystallinity would be positively correlated actually holds true on the microscopic scale for these samples. 18 refs. 

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