POLARISED OPTICAL MICROSCOPY

The liquid crystal properties of the complexes were characterised using polarised optical microscopy and showed a nematic phase for n = 4 and 6 and a SmA phase for n = 6, 8, 10 and 12. The mesophases were monotropic for n = 4 and 6 and enantiotropic for the others the progression from a nematic phase for shorter chain lengths to SmA at longer chain lengths is quite typical for simple, polar mesogens. 

Such an ordered structure is able to deflect polarised light, so if native starch granules are observed by means of polarised optical microscopy, Maltese crosses will be detected. 

Figure 8.4 Phase contrast microscopy of native (a), gelatinised (c) and destructurised potato starch (e). Polarised optical microscopy of native (b), gelatinised (d) and destructurised (f) potato starch...

Fig. 3.6 Optical microscopy images of transparent carbon crystalline threads obtained in polarised light...

Over the last years the utilisation of supramolecular arrays of surfactant molecules as structure-directing templates [1] has been applied to the synthesis of numerous mesostructured aluminophosphates [2-11]. In most cases the preparations were carried out in aqueous systems under hydrothermal conditions, but tetraethylene glycol and/or unbranched primary alcohols were also used [2,4]. Several discussions have been made on the reaction mechanisms that are involved in the syntheses of mesostructured materials [1,12-15] and recently a number of in-situ investigations on the formation processes of mesostructured silica phases in aqueous media have been reported these studies employed small angle X-ray diffraction [16-19] as well as 2H, 13C, 29Si, and 8lBr NMR spectroscopy and polarised light optical microscopy [17]. 

There are three main techniques used in characterisation of mesophases polarised optical hot-stage microscopy, differential scanning calorimetry (cf. Box 9.1) and small-angle X-ray scattering. 

Thermomicroscopy is the direct observation of a sample (usually) by optical microscopy (often with polarised light) as a function of temperature [1]. Frequently called hot-stage (optical) microscopy , this is a relatively common... 

Polarised light optical microscopy has been used to determine the crystalline structure of the PA 66 matrix in the blends. The micrographs shown in Figure 6 depict a finer PA 66 spherullitic structure in the blend containing the maleated EPR rubber. As was found previously (15), and as seen in figure 6b, the blend with unmodified EPR has a coarser crystal structure. 

If a transition between mesophases has been missed by optical microscopy, then DSC may reveal the presence of a transition at a particular temperature or vice versa. After DSC, the material should be examined very carefully by optical microscopy to provide information on phase stmcture, to check that transitions have not been missed by DSC and hopefully to lead to the likely identity of the mesophases. Accordingly, optical polarising microscopy and differential scanning calorimetry are significant, complementary tools in the identification of the types of mesophases exhibited by a material. 

Figure 17.11 Photograph of a chiral nematic cellulose film (a) and its optical microscopy image in cross polarisation configuration (b).

Sampling and subsequent preparation techniques determine the nature and extent of useful information obtained [33]. Microtomy is probably the best technique. To preserve the microstructure, it is advisable to embed, grind and polish the sample. Unfilled plastic samples for optical microscopy are prepared by using a microtome to cut thin sUces, typically 3-20 fim thick, fi om the plastic part. These slices are then placed between two glass slides and examined using transmitted polarised Ught. Magnifications up to lOOOx are typically used. Thus, optical microscopy allows one to see the microstructure of the plastic. 

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