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Dicyanamide Salts that Adopt Smectic, Columnar, or Bicontinuous Cubic Liquid‐Crystalline Mesophases
Author(s) -
Park Geonhui,
Goossens Karel,
Shin Tae Joo,
Bielawski Christopher W.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201705794
Subject(s) - thermotropic crystal , dicyanamide , ionic liquid , thermogravimetric analysis , crystallography , counterion , differential scanning calorimetry , materials science , liquid crystal , eutectic system , phase (matter) , chemical engineering , chemistry , organic chemistry , thermodynamics , liquid crystalline , ion , microstructure , optoelectronics , physics , engineering , catalysis
Abstract Although dicyanamide (i.e., [N(CN) 2 ] − ) has been commonly used to obtain low‐viscosity, halogen‐free, room‐temperature ionic liquids, liquid‐crystalline salts containing such anions have remained virtually unexplored. Here we report a series of amphiphilic dicyanamide salts that, depending on their structures and compositions, adopt smectic, columnar, or bicontinuous cubic thermotropic liquid‐crystalline mesophases, even at room temperature in some cases. Their thermal properties were explored by polarized light optical microscopy, differential scanning calorimetry, thermogravimetric analysis (including evolved gas analysis), and variable‐temperature synchrotron X‐ray diffraction. Comparison of the thermal phase characteristics of these new liquid‐crystalline salts featuring “V‐shaped” [N(CN) 2 ] − anions with those of structural analogues containing [SCN] − , [BF 4 ] − , [PF 6 ] − , or [CF 3 SO 3 ] − anions indicated that not only the size of the counterion but also its shape should be considered in the development of mesomorphic salts. Collectively, these discoveries may be expected to facilitate the design of thermotropic ionic liquid crystals that form inverted‐type bicontinuous cubic and other sophisticated liquid‐crystalline phases.