Dr. Oleg Lavrentovich
"Lyotropic Chromonic Liquid Crystals"
Figure 1. Molecule of disodium cromoglycate.
Lavrentovich’s group explores a new broad class of liquid crystals, the so-called lyotropic chromonic liquid crystals (LCLCs).1 LCLCs promise exciting applications in biosensing, drug delivery, fabrication of films with anisotropic optical and semiconducting properties.2, 3 LCLCs are comprised of plank-like molecules with a polyaromatic central core and ionic groups at periphery (Fig. 1). The basic building block of LCLCs is an aggregate in which the molecules are arranged face-to-face. The soft non-covalent character of aggregation poses a fundamental question about elasticity of LCLCs that will be addressed in this project. Recently, our group measured for the first time the elastic constants of LCLCs and found their behavior to be very different from that one in thermotropic LCs. For example, the splay constant shows a dramatic reduction when the temperature increases, a feature intimately associated with the shortening of aggregates at high temperature and causing spontaneous chiral symmetry breaking.4
We propose to explore how the elasticity of LCLC depends on the ionic content of solutions, on pH and presence of salts; the issue is of prime importance in biosensing applications.5 One can expect two competing mechanisms. First, at a higher ionic strength, the electric charges are better screened, which allows the aggregates to grow longer, thus enhancing the elastic rigidity. On the other hand, the screening shortens the persistence length of aggregates, so that the material can become more flexible. We will explore the LCLCs such as disodium cromoglycate and sunset yellow, doped with salts such as NaCl and MgCl2.6 We will use the magneto-optical set-up that determines the threshold of LCLC distortions in the magnetic field.7 The students will learn how to prepare liquid crystals, how to identify their orientation under a polarizing microscope, how to measure optical phase retardation as a function of the magnetic field and how to extract the values of elastic constants from the magneto-optical data.
- J. Lydon, Chromonic liquid crystalline phases, Liq. Cryst. 38, 1663-1681 (2011).
- H.-S. Park and O. D. Lavrentovich, Lyotropic chromonic liquid crystals: Emerging applications, In: Liquid crystals beyond displays: chemistry, physics and applications, Editor: Quan Li, Chapter 14, 449-484, Wiley (2012).
- C.J. Woolverton, E. Gustely, L. Li, O.D. Lavrentovich, Liquid crystal effects on bacterial viability, Liq. Cryst. 32, 417-423 (2005).
- L. Tortora and O.D. Lavrentovich, Chiral symmetry breaking by spatial confinement in tactoidal droplets of lyotropic chromonic liquid crystals, Proc. Natl. Acad. Sci. USA 108, 5163-5168 (2011).
- S. Shiyanovskii, T. Schneider, I.I. Smalyukh, T. Ishikawa, G.D. Niehaus, K.J. Doane, C.J. Woolverton, and O.D. Lavrentovich, Real time microbe detection based on director distortions around growing immune complexes in lyotropic chromonic liquid crystals, Phys. Rev. E 71, 020702 (2005).
- H.-S. Park, S.-W. Kang, L. Tortora, Y. Nastishin, D. Finotello, S. Kumar, and O.D. Lavrentovich, Self-assembly of lyotropic chromonic liquid crystal sunset yellow and effects of ionic additives, J. Phys. Chem. B 112, 16307-16319 (2008).
- S. Zhou, Yu.A. Nastishin, M.M. Omelchenko, L. Tortora, V.G. Nazarenko, O.P. Boiko, T. Ostapenko, T. Hu, C.C. Almasan, S. N. Sprunt, J.T. Gleeson, O.D. Lavrentovich, Elasticity of lyotropic chromonic liquid crystals probed by director reorientation in a magnetic field, Phys. Rev. Lett. 109, 037801 (2012).