First Examples of deVries-like SmecticA to SmecticC Phase Transitions in Ionic Liquid Crystals

• Published in: Chemphyschem Vol. 17; no. 24; p. 4116
• Main Authors: Kapernaum, Nadia, Muller, Carsten, Moors, Svenja, Schlick, M Christian, Wuckert, Eugen, Laschat, Sabine, Giesselmann, Frank
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 15-12-2016
• Subjects: Ions; Solvents
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201600829

In ionic liquid crystals, the orthogonal smecticA phase is the most common phase whereas the tilted smecticC phase is rather rare. We present a new study with five novel ionic liquid crystals exhibiting both a smecticA as well as the rare smecticC 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 deVries character. Four of our five mesogens turned out to show deVries-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 deVries-type materials among ionic liquid crystals.