Assembly structure and free energy change of a chromonic liquid crystal formed by a perylene dye

ABSTRACT

The nematic (chromonic N) and isotropic phases formed by aqueous solutions of a perylene dye are investigated by x-ray diffraction and visible light absorption spectroscopy. X-ray diffraction shows that the molecules assemble into columns one molecule wide. The change in the visible absorption spectrum with concentration indicates that the molecules stack in a more or less isodesmic manner and that the free energy change associated with the addition or removal of a single molecule from a stack is 16–20 $k_{B}T$. This range is appreciably higher than those of any previously-measured simple chromonic systems, i.e. those with single molecule-wide columns. It is suggested that the large free energy change promotes the formation of extremely long columns of molecules, and in turn leads to the low concentration at which mesophase formation takes place.

Graphical abstract

KEYWORDS:

• Liquid crystals
• lyotropic chromonic
• chromonic
• scission energy
• isodesmic
• perylene dye
• assembly structure

Acknowledgments

The authors thank Suk-Wah Tam-Chang (then of the University of Nevada, Reno, now at the National Science Foundation) for supplying the PDI sample and Paul Heiney (University of Pennsylvania) for help with the x-ray experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was partially supported by the National Science Foundation through the University of Pennsylvania Materials Research Science and Engineering Center (MRSEC), Grant Nos. DMR11-20901 and DMR17-20530. T. O. acknowledges research support from Swarthmore College.