Lamellar focal conics

Fig. 3 Lamellar focal conics under the polarization microscope using color contrast by means of a 2, mask...

Lamellar focal conics show a fascinating highly-ordered structure when observed under the polarization microscope. This texture consists of surfactant bilayers that are shaped like ice cream cones and stuck inside of one another. These stacks of cones are quite densely packed in the solution and, under the polarization microscope, create extended regions of amazing regularity. Figure 3 shows a photograph of such a system, taken with a polarization microscope with a A mask to achieve color contrast. 

What is most amazing of all in this picture is the degree of microscopic order present in a solution that appears quite unexceptional to the imaided eye. Usually, we associate T>eauty and aesthetic appeal with symmetry and regular shapes, just as in the examples of the ordered lamellar phase and lamellar focal conics. However, sometimes also asymmetric shapes have that special quaUty about them that conveys what we call beauty. Figure 4 shows a water-rich foam composed of dish soap with coconut oil. It consists of tightly-packed bubbles of very different sizes that create an asymmetric pattern of astounding beauty [3]. 

The stmcture of the SmA phase does not change if the mesogens are chiral, but some of its properties do, e.g. the response to an applied electric field [21], Therefore, the chiral SmA phase is denoted as SmA. Between crossed polarizers, the SmA, the SmA as well as the lamellar L phase initially form so-called batonnets under planar anchoring conditions if emerging directly from the isotropic phase. These batonnets then condense into a focal conic fan-shaped textiue. If the director is oriented parallel to the viewing direction, the texture appears black between crossed polarizers, which is referred to as homeotropic . It is also possible to find oily streaks within the homeotropic texture, if the alignment of the sample is imperfect. 

Figure 5.16b shows a broken fan texture, which results from cooling down the sample from the focal conic fan texture of the lamellar L phase. The continuity of the fans suggests that the lamellar structure persists at the phase transition. However, the breaking of the fans again indicates the formation of a tilted structure. 

The case of homeotropic alignment is quite easy to envisage and is identical to the situation described for the nematic liquid crystal phase except for the lamellar nature of the phase. However, the focal-conic formation is more complex and more commonly... 

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