Influence of semiperfluorinated chains on the liquid crystalline properties of amphiphilic polyols: Novel materials with thermotropic lamellar, columnar, bicontinuous cubic, and micellar cubic mesophases

Novel amphiphilic diols with semifluorinated alkyl chains have been synthesized. These are 1-benzoylaminopropane-2,3-diols carrying one, two, or three semiperfluorinated chains at the aromatic core, as well as a 2-benzoylaminopropane-1,3-diol and a 2-benzoylaminoethanol with two semiperfluorinated chains. Their thermotropic liquid crystalline properties were investigated by means of polarizing microscopy, differential scanning calorimetry, and X-ray diffraction. In comparison with the related hydrocarbon compounds, the semifluorinated analogues have significantly more stable mesophases. Because of the larger cross-sectional area of the perfluorinated segments, not only the three-chain compounds but also most two-chain compounds have reverse discontinuous (micellar) cubic mesophases (Cub(I2)). Additionally, phase diagrams of binary systems of a single-chain amphiphile with the two- and three-chain amphiphiles have been investigated. Hexagonal columnar (Col(h2)) and bicontinuous cubic phases (Cub(V2)) were induced in such systems. Remarkably, the Cub(V2) phases occur only above a distinct temperature, whereas at lower temperature a direct transition between the lamellar phase and the columnar phase takes place. This leads to a reentrant, behavior of the smectic A phases and columnar phases in certain concentration ranges.