Microscopy polarised light

W. C. McCrone, L. C. McCrone, and J. G. DeUy, Polarised Light Microscopy, Ann Arbor Science PubHshers, Inc., Ann Arbor, Mich., 1979. 

Reflected light Microscopy can be used for examining the texture of solid opaque polymers. Materials which can be prepared as thin films are generally examined by transmitted light. Two common techniques used are (i) polarised-light Microscopy, and (ii) phase contrast Microscopy. 

The existence of crystal lamellae in melt-crystallised polyethylene was independently shown by Fischer [28] and Kobayashi [39]. They observed stacks of almost parallel crystal lamellae with amorphous material sandwiched between adjacent crystals. At the time, another structure was well known, the spherulite (from Greek meaning small sphere ). Spherulites are readily observed by polarised light microscopy and they were first recognised for polymers in the study of Bunn and Alcock [40] on branched polyethylene. They found that the polyethylene spherulites had a lower refractive index along the spherulite radius than along the tangential direction. Polyethylene also shows other superstructures, e.g. structures which lack the full spherical symmetry referred to as axialites, a term coined by Basset et al. [41]. 

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). 

When a bulk material is submitted for analysis, the laboratory should be able to locate and identify very small quantities of asbestos within the sample matrix. Polarised light microscopy methods should be able to detect 0.01% (lOOmg/kg) asbestos if there are no interfering factors, however the majority of building materials or products contain concentrations ranging from virtually 100% asbestos down to around 1% and therefore it should not be difficult to correctly identify whether or not asbestos is present in the majority of routine samples. 

MDHS 77 (1994) Asbestos in bulk materials, sampling and identification by polarised light microscopy (PLM), June 1994, ISBN 0-7176-0677-5. 

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. 

Fig. 2 Diversity of supramolecular structures obtained from food proteins, (a) TEM micrograph of fibrils obtained after heating a mixture of p-lactoglobulin (P-Lg) and a-lactalbumin (a-La) (2.5 wt% with ratio p-Lg to a-La of 90 10) at pH 2 [adapted with permission from Bolder et al. [73] (2006) fi-om ACS], (b) AFM micrograph of p-Lg ribbons obtained after heating p-Lg (2 wt%) at 90°C and pH 2 [reprinted with permission from Lara et al. [23] (2011) from ACS], (c) Polarised light microscopy micrograph of spherulites formed from p-Lg [reproduced with permission fi om Krebs et al. [74] 2009 from The Biochemical Society], (d) TEM micrograph of p-Lg dispersion (1 wt%) after heating at 85°C for 15 min at pH 5.8 [adapted with permission from Schmitt et al. [75] (2009) from ACS]...

Morphology of the polymer at and away from the surface of the additive particles, is conveniently determined by polarised light microscopy and, where higher resolution is required, by electron microscopy. More detailed consideration of the effects of particulate additives on polymer crystallinity is presented elsewhere in this book. 

Wney, C. Transmitted Polarised Light Microscopy. Chicago McCrone Research Institute, 1990. 

PLM Polarised light microscopy RAE Resistive anode encoder... 

Perhaps the most widely used application of polarised light microscopy in the study of polymers is in connection with crystalline morphologies [21-30]. Figure 10.5 shows typical spherulites of the a crystal form of poly(vinylidene fluoride), as imaged in polarised light. The extinction pattern seen in Figure 10.5(a) is made up of a black Maltese cross, a feature that is typical of a... 

TGA, dynamic rheological analysis and polarised light microscopy were used to assess thermal stability of PEEK. Emphasis is given to the effect of melting temperature on thermal stability. 23 refs. 

Lamellar arrangements were detected by polarised light microscopy. DSC and XRD confirmed that chains of emulsifier were in the crystalline state. Ternary systems with liquid paraffin were isotropic, homogenous o/w creams for a wide composition range. Incorporation of 50 mol % cholesterol lead to the separation of a gel-liquid crystalline phase within the layer [174]. The transition energies, derived from DSC, decreased linearly with increasing cholesterol concentration. Optical microscopy should be used to confirm phase separation in creams [175]. 

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