Texture of the Cholesteric Unwinding Region

Texture of the Cholesteric Unwinding Region

The transition region between cholesteric and high density phases in solutions of rod-like DNA molecules is the subject of debate. The structure of the mesophase in this region is largely unknown, but is believed to involve an unwinding of the cholesteric phase in a transition to a more highly ordered hexatic phase. The image above captures this mesophase as a birefringent area devoid of recognizable texture. The DNA concentration for this specimen was initially 100 milligrams per millimeter, but this changes as the solvent evaporates. The magnification is approximately 300x. Originally recorded on Fujichrome 64T transparency film using a Nikon Optiphot-Pol microscope with crossed polarized illumination, the image above was digitized using a Nikon CoolScan transparency film scanner. Exposures were recorded about 3 f-steps under the recommended value given by an in-camera photomultiplier and were push-processed approximately 1.75 f-steps in the first E-6 developer.


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