LIQUI1) CRVSTALS 587 .½. Figure 6. Neat phase (left) showing te•aced edge at interface with isotropic solution (right). Some te•aces are above co•ect focus and some below. Ordinary light, magnification ca. 150X Figure 7. Neat phase. Bright bands (oily streaks) with complex focal conic detail. Black circles are air bubbles. Irregular black areas are neat phase in planar orientation. Crossed polarizers, magnification ca. 80X used to identify or locate mesomorphic phases, the most widely used is the polarizing microscope. The structural differences between phases are evident in the microscope as patterns or "textures" which constitute a convenient and dependable method for identification (9). Such differentiation of several mesomorphic phases is illustrated in Fig. 5, which was obtained by allowing a drop of water to diffuse into a group of surfactant crystals placed under a cover glass on the micro- scope slide. In succession can be seen crystals, neat phase, viscous isotropic phase, and middle phase. Figures 7 through 14 are representative polarized-light textures of individual phases. Figure 7, although it is all neat, gives the impression of two phases. However, the irregular black areas arise from the fact that the smectic layers are parallel to the surface of the slide ("planar" ß arrangement) and the light is traveling along the "optic axis" of the structure, its nonbirefringent direction. The bright bands in the same figure are so-called "oily streaks" (1) in which the molecular layers are not planar but arranged in the complex "focal conic" (1) pattern, a characteristic equilibrium configuration of the smectic structure. Another characteristic focal conic appearance is the complex network of

588 JOURNAL OF THE SOCIETY OF COSMETIC CHEhlISTS ß Figure 8. Neat phase. Coarse mosaic texture showing "positive" extinction- crosses (narrow centers) and "negative" crosses (broad centers) with both straight and curve4 arms. Crossed polarizers, magnification ca. 1.50X .,'..-22. • •' ..ß. .: "22'..-2 'ß. "i ' - ' ? ' ' Figure O. Neat phase. Typical fine mosaic. Crossed polarizers, magnifica- tion ca. .. . .' ,•:" •:' •* -' '-•*. '?..-'.' .. l'" • . •, .l•: I ,,l F•gure 10. Middle phase. Nongeo- metric [ex[ure, s[ria[ed. Cros•d polar- izers, magnifica[ion -' i "-- •. - . ': .. •- •. •½ :-- •' .•' :: ...... ' .:.... { , '. -• ? ..... . . -•.. Figure 11. •iddle phase. Angular tex- ture. Crossed polari•rs, magnification ca. 50X