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Magnetic Field Alignment of the Cholesteric and High Density Mesophases in Liquid Crystalline DNA - In the presence of a magnetic field, the liquid crystalline nematic director vector will tend to align relative to the field. Because DNA has a negative anisotropy in diamagnetic susceptibility, the molecular helices align perpendicular to an applied magnetic field, which orients the twist axis of the cholesteric phase in a manner parallel to the field. The links below lead to photomicrographs and discussions of magnetic field effects on liquid crystalline DNA.

Magnetically aligned samples subjected to controlled drying were used to obtain initial measurements of the cholesteric helical pitch change with concentration in calf thymus liquid crystalline DNA. In the transition region, these samples exhibited a continuous increase in pitch from about 2.5 to 5 micrometers. With further increase in DNA concentration, the morphology becomes disordered and difficult to interpret. These regions exhibit a high degree of birefringence and higher order interference colors. At still higher DNA concentrations, the morphology once again appears cholesteric, with the twist axis again parallel to the direction of applied magnetic field and varying from 8 to 10 micrometers.

This research was conducted in collaboration with Dr. Randolph L. Rill of the Department of Chemistry and Institute of Molecular Biophysics and Dr. David H. Van Winkle of the Center for Materials Research and Technology at the Florida State University.


Magnetic Field Alignment of the Unwinding Region - X-ray scattering and optical microscopy studies have revealed a dramatic increase in the cholesteric helical pitch of liquid crystalline DNA in the transition region to a higher density mesophase. The image in this section illustrates the formation of batonnets within the confines of an unwinding cholesteric phase that has been aligned with a 7 Tesla magnetic field.

Magnetic Field Effects on Cholesteric Helical Pitch - The image in this section illustrates the effects of a high magnetic field (7 Tesla) on the cholesteric helical pitch at the cholesteric/high density transition boundary. Orientation of the cholesteric phase by the magnetic field has resulted in an increase in the helical pitch of this phase to approximately 10 microns.

Magnetic Field Alignment of the Liquid Crystalline DNA Cholesteric Phase - Long-range orientation of cholesteric liquid crystalline DNA mesophases occurs at magnetic field strengths exceeding 2 Tesla. The image presented in this section illustrates this long-range order in DNA solutions approaching 300 milligrams per milliliter.

Batonnet Formation in Magnetically Aligned DNA Liquid Crystals - Orientation of the transition region with a 5 Tesla magnetic field increases the helical pitch of the unwinding cholesteric mesophase, which is spontaneously forming batonnets during the phase transition as is evident in the image presented in this section.

Perturbations of the Cholesteric Mesophase - Miniature gas bubbles trapped in the liquid crystalline DNA sandwich between a microscope cover glass and slide disturb orientation of the cholesteric phase by high magnetic fields.

Chevron Structures in the Cholesteric Mesophase - When cholesteric liquid crystalline DNA is oriented in a magnetic field, the regions containing low-density mesophases acquire a texture that resembles a repeating chevron structure.

Batonnet Alignment by High Magnetic Fields - During controlled drying experiments, batonnets formed at the interface between cholesteric and high density liquid crystalline DNA are oriented with respect to externally applied magnetic field direction vectors.

Phase Transitions in High Magnetic Fields - Phase transitions between the cholesteric and high density liquid crystalline DNA phases occur with the formation of batonnets during unwinding of the cholesteric mesophase.

Unusual Phenomena in Cholesteric Mesophases - An ordered phase of indeterminate structure occurs in the cholesteric mesophase in liquid crystalline DNA samples exposed to high magnetic fields. This phase exhibits a high degree of birefringence with higher order colors that suggests a complex structure that does not appear to occur in the absence of the magnetic field.

Birefringent Regions in Cholesteric Mesophases - Birefringent regions of indeterminate structure occur in the cholesteric mesophase of liquid crystalline DNA samples exposed to high magnetic fields. The photomicrograph presented in this section illustrates a region having strong birefringence and exhibiting a wide spectrum of higher order colors, which may be due to thickness variations.

Phase Transitions at Low Magnification - Phase transitions in magnetically aligned liquid crystalline DNA specimens are dependent upon the direction of the phase transition with respect to the magnetic field director vector and concentration gradient.

Cholesteric Unwinding in the Phase Transition Region - The cholesteric liquid crystalline DNA phase begins to unwind and form batonnets at the interface between this phase and the higher density hexatic phase.

Batonnet Formation at Low DNA Concentrations - The rate of controlled drying in DNA liquid crystalline phase transition experiments often determines many characteristics exhibited by the textures observed in the microscope. The image presented in this section was made with a very slow rate of drying that results in batonnet formation within the cholesteric mesophase.

Ordered High Density Phase Growth in Magnetic Fields - High density liquid crystalline DNA phase development occurs in a very orderly fashion when influenced by a combination of an established concentration gradient and high magnetic fields.

Longitudinal Batonnet Formation - The growth orientation of batonnets is dependent upon the concentration gradient and the magnetic field director vector in controlled drying experiments. The photomicrograph presented in this section illustrates batonnet formation when the concentration gradient is parallel to the magnetic field.

Longitudinal Batonnet Formation - The growth orientation of batonnets is dependent upon the concentration gradient and the magnetic field director vector in controlled drying experiments. The photomicrograph presented in this section illustrates batonnet formation when the concentration gradient is perpendicular to the magnetic field.

Batonnet Formation in Low Density Cholesteric Mesophases - Batonnet formation often initiates in low density cholesteric mesophases. The image presented in this section is a magnetically-aligned cholesteric phase with a DNA concentration of approximately 200 milligrams per milliliter.


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