Origin of the Director Tilt in the Lyotropic Smectic C* Analog Phase: Hydration Interactions and Solvent Variations

The origin and long‐range correlation of the director tilt in the recently discovered 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 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 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 phase is indeed reduced by this modification of the solvent′s hydrogen bond network.