Mesogenic Structures, Lyotropic and Thermotropic Phase Transitions in Demethyl-Ionene Alkyl Sulfonate Complexes

Linear [B,10]-polyamines [(CH2)BN(CH3)(CH2)10N(CH3)] were prepared (B = 3 or 6). Protonated by stoichiometric amounts of n-alkylsulfonic acids, they form demethyl-ionene sulfonate complexes, which proved thermally stable up to 220 °C. Salt free complexes were investigated by polarized microscopy, thermogravimetry, and X-ray diffraction. Except the heptyl sulfonate, which crystallized, all complexes bearing longer alkyl chains formed mesogenic phases. Being isotropic in dry state, they became optically anisotropic when exposed to humidity due to a lyotropic transition (mediated by the gas phase) to a hexagonal phase, mostly. A cubic phase containing less water was also observed. Anisotropic complexes again were converted to an isotropic state upon heating under controlled humidity. The clearing temperatures distinctly depend on humidity and rise with increasing length of the alkyl sulfonate. This may allow the use of the complexes as humidity sensors. Oriented liquid crystalline samples are formed upon fast cooling in flat capillaries.