Textures chromonics

A general correspondence between the optical textures, the X-ray diffraction patterns, and the forms of the phase diagrams has been observed for chromonic drugs and many dye/water systems [4-7]. The only significant difference between these two families of mesogens appears to be in some optical textures and rheological properties... 

In optical examinations of chromonic systems, the textures of both the one-phase and the two-phase regions tend to be highly characteristic [46]. The N phase usually... 

One of the sources of confusion to early workers in the field was the way in which chromonic textures depend on the past history of the sample. A one-phase or two-phase region may have dramatically different textures depending on whether it has been reached by heating or cooling, by con-... 

Figure 6. The explanation for the tiger skin texture sometimes adopted by chromonic N (and P) phases The banded pattern seen with crossed polars is thought to result firom a twisted rope-like arrangement of the columns. Such a pattern could be a way of accommodating initial misalignment in the sample with a minimum of splay distortion, (a) The postulated arrangement of molecular stacks in two adjacent twisted ropelike assemblies, (b) The gross structure of the sample showing the large-scale organization of the assemblies represented in (a), (c) The banded appearance of a sample when viewed vertically between crossed polars.

Note that the term herringbone is used in two different contexts in chromonic systems at the molecular level, to describe the transverse arrangement of columns in the M phase, and on a much larger scale, to describe the diagonally striped optical texture of the M phase grown by concentration of the N. 

Chromonic phases can in general be oriented by surface alignment or magnetic fields, but when samples are introduced into untreated glass tubes for an X-ray study, there is usually sufficient spontaneous alignment for axial and equatorial reflections to be easily distinguished. (In rare cases a sample in the M phase will form a large scale zig-zag texture like that observed by Bernal and Fankuchen for TMV solutions [49].)... 

The fingerprint texture of a chirally doped chromonic drug N phase. This sample shows the N -t I phase of a 5% solution of arginine in a 22% sample of DSCG at room temperature. The separation of the striations corresponds to 1/2 the pitch of the helicoidal structure. (x300, crossed polars.)... 

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