Microscopy transmitted light

When a beam of light travels through a sample it is modified as a result of the optical properties of the material and their spatial variation within the specimen. In samples where the absorption coefficient varies from place to place this naturally leads to contrast in the final image. However, of more interest, as far as many polymers are concerned, are techniques that enable differences in other optical properties to be imaged. 

In both bright-field and oblique illumination, the undeviated incident beam, after passing through the sample, falls within the limits of the objective lens. 

Transmission optical micrograph taken using oblique illumination in a hot stage (compare 

However tlie ofeUqutty of the illOTtination can be increased to such an extent that undeviated rays pass outside the objective lens. In practice, dark field 

3 Phase-contrast microscopy. In bright-field illumination, variations in optical absorption within the specimen give rise to an image which consists 

---

Fusain black macroscopic coal constituent (lithotype) that resembles wood charcoal extremely soft and friable. Also, U.S. Bureau of Mines term for mineral charcoal seen by transmitted light microscopy. See also Coal. 

Figure 9. Fracture surface of polymerized acrylic dispersion (67 vol % beads), polarized transmitted light microscopy 68 X...

FIGURE 1.2 Fiber bundle cross-sections obtained with transmitted light microscopy (a) for natural brown cotton where the presence of material bodies are visible within the lumens of some fibers and (b) for natural green cotton where the fibers are quite immature and are chacterized by the presence of suberin in the fiber walls and not material bodies in the lumen. 

Figure 1.44 Micrographs of asphalt-polyolefin elastomer (POE) blend obtained with transmitted light microscopy (a) bright-field image that cannot reveal the two phases in the blend and (b) a fluorescence-labeled image that reveals two-phase morphology. (Reproduced with permission of Jingshen Wu.)...

In 1980, Perron, Bayer, and Wiedemann described a combination of differential thermal analyzer and transmitted-light microscopy based on the Mettler FP-5 hot-... 

Morrow (52) has described a DTA-light photometer polarizing system for hot-stage microscopy. Thermocouple wires. 0.003 in. in diameter, were used to detect the 7 — Tr) temperature difference fo r simultaneous DT A measurements. Sample capsules were fabricated by bending small, identical stripes of AI foil over both sample and reference thermojunctions. A small hole in the foils permitted the viewing of the sample by transmitted light microscopy. The primary use of the apparatus was to study the thermal properties of thermally sensitive polymers (84). 

Transmitted light microscopy requires a sample sufficiently thin to allow light to pass through the sample. This is only possible with particulate suspensions in water or light oil. With samples commonly encountered in the petroleum industry, opaque oil components often limit the utility of transmitted light microscopy. In addition, with samples thin enough to be transparent, interactions with the sample holder have to be understood. 

Previous work with flowing suspensions of red cells has shown that they can remove surface-bound molecules e g. cholesterol (24). fibrinogen (25) and albumin (25). Adherent platelets have longer residence times on a substrate than do red cells and thus can provide different effects. Detached platelets are likely to be altered from their natural state and thus be predestined, in an artificial organ flow circuit, for removal from the circulation. Previous work using transmitted light microscopy which dealt with platelet adhesion and detachment was limited in that the flow rate range was low as was the concentration of... 

Ono described the polymorphs of dicalcium silicate with transmitted-light microscopy and X-ray diffraction (XRD) in 1953, confirming the occurrence of alpha-prime, beta, and gamma forms. 

Ono, Kawamura, and Fujimura in 1964 described the sequence of reactions that occur during sintering of powders of calcite, clay, siliceous rock, and copper slag (an iron bearing glass) through chemistry, XRD, and transmitted light microscopy. 

Specimen preparation may be broadly classified into two main areas specimen preparation techniques for transmitted-light microscopy (thin sections, smears, fibers, particulate strews) and specimen preparation techniques for reflected-light microscopy (surface preparation of opaque and nearly opaque materials). However, they are by no means exclusive and, although metals, ores, and opaque minerals may be studied by reflected light only, thin sections, smears, etc., may be studied both by transmitted and by reflected light, e.g., transmitted-light and epifluorescence microscopy. The advantages of such dual observational techniques relate in particular to contrast enhancement (criterion (3)). 

R. D. Allen el al. The Zeiss Nomarski Differential Interference Equipment for Transmitted-Light Microscopy. Z. Wiss. Mikrosk. Mikrosk. Tech, 69 (1969) I93-22I. 

Just as important as the proper use of the microscope is the specimen preparation. When using transmitted-light microscopy, it is necessary to prepare thin samples, about 5-50 pm thick. This is also true even for transparent polymers because of the small depth of field of an optical microscope. If information is required about an inner part of the material, the only course of action is to cut a thin section with a microtome. Melt-pressed films can be prepared by melting the polymer and squeezing it between two glass slides to make it thin. Many of the generally known specimen preparation methods are applicable to polymers. A recent overview of all methods as a useful tool for polymers is given in [Ij. 

---