Polaroids

Suppose a bulk-crystallized polymer sample is observed in an optical microscope with the sample placed between Polaroid filters oriented at right angles to each other. In the absence of any sample, the light would be attenuated owing to the 90° angle between the vectors describing the light transmitted by the two filters. With a crystalline sample of polymer in place, however, a display like... 

Figure 4.12 Spherulites of poly( 1-propylene oxide) observed through crossed Polaroid filters by optical microscopy. See text for significance of Maltese cross and banding in these images. [From J. H. MaGill, Treatise on Materials Science and Technology, Vol. lOA, J. M. Schultz (Ed.), Academic, New York, 1977, with permission.]...

The individual spherulite shows up by the characteristic Maltese cross optical pattern under crossed Polaroids, although the Maltese cross is truncated in the event of impinging spherulites. 

The molecular chain folding is the origin of the Maltese cross which identifies the spherulite under crossed Polaroids. The Maltese cross is known to arise from a spherical array of birefringent particles through the following considerations ... 

This birefringence coupled with spherical geometry produces light extinction along the axis of each of the Polaroid filters, hence the 90° angle of the Maltese cross. 

If the Polaroid filters are held fixed and the sample rotated between them, the Maltese cross remains fixed because of the symmetry of the spherulite. 

Polaroid DMP128 Holographic Material, Cambridge, Mass. 

Venus probe. References should be consulted for the details of the optical transparency of the different type diamonds (9,14,16—19). The direct band gap for diamond is 5.47 eV. Natural diamond exhibits many colors, and color modification by irradiation and annealing is common (36). Though cubic, most natural diamonds show strain birefringence under crossed polaroids. 

The first instant color photography system, introduced by the Polaroid Corp. in 1963 as Polacolor, used the transfer of subtractive dyes to a receiver sheet to produce a positive image. The incorporated dye-developers, containing a hydroquinone moiety, are soluble in the alkaline activator solution, except where silver development occurs, when they are immobilized as the quinone form. 

Discrimination between exposed and unexposed areas in this process requires the selection of thia zolidine compounds that do not readily undergo alkaline hydrolysis in the absence of silver ions. In a study of model compounds, the rates of hydrolysis of model /V-methyl thia zolidine and A/-octadecyl thiazolidine compounds were compared (47). An alkaline hydrolysis half-life of 33 min was reported for the /V-methyl compound, a half-life of 5525 min (3.8 days) was reported for the corresponding V/-octadecyl compound. Other factors affecting the kinetics include the particular silver ligand chosen and its concentration (48). Polaroid Spectra film introduced silver-assisted thiazolidine cleavage to produce the yellow dye image (49), a system subsequentiy used in 600 Plus and Polacolor Pro 100 films. 

Polaroid additive color screen silver transfer process Super-8 film 35-mm films... 

Polacolor. The first instant color film, Polacolot, was introduced by Polaroid Corporation in 1963. Polacolot was replaced in 1975 by Polacolot 2, a film with improved light stabiUty, which utilizes the metallized dye developers shown in Eigute 4. An extended range version, Polacolot ER, introduced in 1980, utilizes the cyan and yeUow metallized dye developers together with a magenta dye developer that incorporates a xanthene dye having reduced blue absorption (see Eig. 5). 

Polaroid Integral Films. In 1972 the SX-70 automatic camera and integral film system were introduced (12,13). The SX-70 film provided images that required no timing and no peeling apart. Each film unit was ejected through processing rollers immediately after exposure. The entire development process took place within the film unit under ambient conditions. 

The integral film format required different processing chemistry and film components from those used previously. The processed film unit needed to contain all of the reaction products along with the final color image. Polaroid followed the original SX-70 film with Time-Zero SX-70 film (1979), 600 film (1981), Spectra film (1986), and 600 Plus film (1988). 

The reduction of pH within the film unit is effected by a polymeric acid layer, as in the Polacolor process. The onset of neutralization is controlled by a contiguous timing layer. In the original SX-70 film unit these layers were on the inner surface of the transparent polyester sheet (Fig. 12) in Time-Zero SX-70 and later Polaroid integral films these layers are on the inner surface of the opaque negative support, as shown in Figure 13. 

Fig. 13. Schematic cross section of Time-Zero SX-70 integral film. In this film the polymeric acid layer and the timing layer are located beneath the negative layers, rather than in the positive sheet. Time-Zero and all later Polaroid integral films have an antireflection layer coated on the outer surface of the clear...

Polaroid introduced Polavision, a Super-8-mm instant motion picture system, in 1977 (97). Polachrome CS 35-mm sHde film followed in 1982 (98), and a high contrast version, Polachrome HCP, appeared in 1987. Each of the films comprises a very fine additive color screen and an integral silver image transfer film. The Polavision system, which included a movie camera and a player that processed the exposed film and projected the movie, is no longer on the market. The Polavision film was provided in a sealed cassette, and the film was exposed, processed, viewed, and rewound for further viewing without leaving the cassette (97). 

Polachrome is provided in standard-size 35-mm cassettes. Its processing is carried out in a Polaroid Autoprocessor using a processing pack that contains a reagent pod and a strip sheet (98). 

Instant films accounted for 10.9% of film sales in 1989 (105), and there were 12 million instant cameras in use in the United States in 1988 (106). Polaroid reported sales of about 3.1 million consumer cameras worldwide in 1990, compared with 3.0 million in 1989 and 3.5 million in 1988 (107). In Japan, Fuji accounted for 6% of instant camera sales and Polaroid for 94% in 1989 (108). Fuji has estimated 1991 sales of instant cameras in Japan, including Polaroid cameras, at 400,000 (109). 

Fig. 23. An example of fundus (retinal) photography, widely used for diagnosis in opthamology. The photograph is on Polaroid Type 779, a professional...

Fig. 24. A thin layer chromatography (TLC) image, documenting detection of impurities in a series of dye intermediate samples under near-UV illuinination. Columns 1 and 7 represent reference materials. Photographed with Polaroid Type 339 film in a CU-5 closeup camera.

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