University of West Georgia
Subject Listing - Chemistry
Advisor: Dr. Oleg Lavrentovich
Friday, Oral Session 4, Presentation 5, Karpen Hall 034
THE EFFECTS OF MULTIVALENT CATIONS ON THE PHASE DIAGRAMS OF LYOTROPIC CHROMONIC LIQUID CRYSTALS
Lyotropic chromonic liquid crystals (LCLCs) represent a distinct class of liquid crystals formed in aqueous solutions by molecules with rigid polyaromatic cores and ionic groups at the periphery (usually deprived of aliphatic tails). The LCLCs attract a considerable interest because of their potential applications as an amplifying medium in biological sensors. The mechanisms responsible for their mesomorphic behavior are far from being understood well. It is known that molecular self assembly with face-to-face stacking of the aromatic cores results in one-dimensional aggregates with the ionic groups exposed at the aggregate/water interface. These aggregates serve as the building units of the LCLC phases but it is not known whether the interactions among them are of a pure entropic nature or involves electrostatic interactions of the ionic groups. If the latter is of any importance, then the phase diagrams of LCLC should be altered by salts. In this work, we study how the phase stability of the LCLCs is influenced by salts with multivalent cations, such as MgSO4, spermidine, a flexible polyamine molecule with charge 3+, and spermine (4+). The multivalent cations are chosen because unlike their monovalent counterparts they might alter the sign of Coulomb interactions of like-charged rods from repulsion to attraction thanks to their strong correlations. We demonstrate that the phase diagrams of LCLCs are indeed changed dramatically upon addition of the multivalent cations. Depending on the LCLC structure, they cause expansion of either the nematic or isotropic phase, often by tens of degrees. Moreover, the multivalent cations also cause condensation of LCLC aggregates into domains of a new phase with birefringence higher than that of the normal nematic phase. We explain these results qualitatively by considering how the multivalent cations can alter the interactions within the aggregates and between the aggregates.
University of West Georgia, Carrollton, GA 30118
Advisor: Dr. Oleg Lavrentovich, Professor of Chemical Physics and Director, Liquid Crystal Institute (LCI), Kent State University, Kent, OH