title: First Examples of de Vries-like Smectic A to Smectic C Phase Transitions in Ionic Liquid Crystals.
abstract: In ionic liquid crystals, the orthogonal smectic A phase is the most common phase whereas the tilted smectic C phase is rather rare. We present a new study with five novel ionic liquid crystals exhibiting both a smectic A as well as the rare smectic C phase. Two of them have a phenylpyrimidine core whereas the other three are imidazolium azobenzenes. Their phase sequences and tilt angles were studied by polarizing microscopy and their temperature-dependent layer spacing as well as their translational and orientational order parameters were studied by X-ray diffraction. The X-ray tilt angles derived from X-ray studies of the layer contraction and the optically measured tilt angles of the five ionic liquid crystals were compared to obtain their de Vries character. Four of our five mesogens turned out to show de Vries-like behavior with a layer shrinkage that is far less than that expected for conventional materials. These materials can thus be considered as the first de Vries-type materials among ionic liquid crystals.
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Nadia
authors.initials: N
authors.lastname: Kapernaum
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Müller
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Svenja
authors.initials: S
authors.lastname: Moors
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: M Christian
authors.initials: MC
authors.lastname: Schlick
authors.affiliation: Institute of Organic Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Eugen
authors.initials: E
authors.lastname: Wuckert
authors.affiliation: Institute of Organic Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Laschat
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Giesselmann
keywords: X-ray diffraction; ionic liquids; liquid crystals; phase transitions; smectic C phases