title: Origin of the Director Tilt in the Lyotropic Smectic C* Analog Phase: Hydration Interactions and Solvent Variations.
abstract: The origin and long-range correlation of the director tilt in the recently discovered Lα'* phase, which is the lyotropic analog of the thermotropic smectic C* (SmC*) liquid crystalline phase, are investigated. Polarized micro-Raman spectroscopy reveals that the director tilt in the Lα'* phase originates from a tilting of the aromatic 2-phenylpyrimidine cores of the surfactant molecules. Optical measurements of the tilt angle show that its magnitude decreases with increasing solvent concentration, suggesting that the long-range inter-lamellar correlation of the tilt directions is reduced at increasing thickness of the solvent layers. The phase diagrams with four different solvents (water, formamide, N-methylformamide, N,N-dimethylformamide) are investigated, showing that the Lα'* phase is only formed with those solvents that exhibit a dense network of hydrogen bonds. This observation suggests that these hydrogen bond networks play an essential role in the long-range correlation of the director tilt between adjacent surfactant layers. To verify this assumption, mixtures with deuterated solvents are investigated, showing that the tilt angle in the Lα'* phase is indeed reduced by this modification of the solvent's hydrogen bond network.
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Johanna R
authors.initials: JR
authors.lastname: Bruckner
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Friederike
authors.initials: F
authors.lastname: Knecht
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany. f.giesselmann@ipc.uni-stuttgart.de.
authors.forename: Frank
authors.initials: F
authors.lastname: Giesselmann
keywords: Raman spectroscopy; amphiphiles; hydration interactions; liquid crystals; solvent effects