Optical microscopy and deuterium N.M.R. of non-ionic amphiphiles which exhibit thermotropic and aqueous lyotropic mesophases

Abstract

Tetrabenzocyclododecatetraene (I) substituted with eight methoxy-mono-, di-, and triethyleneoxide side chains exhibit the same highly ordered thermotropic mesophase, M. In the methoxydiethyleneoxide (I-2), and methoxytriethyleneoxide (I-3) derivatives this mesophase is also lyotropic and can sustain (at room temperature) up to 40 wt per cent water. The homologue (I-2) exhibits at higher water content another lyomesophase, M_F , which is more fluid and nematic-like. Optical microscopy, differential scanning calorimetry and deuterium N.M.R. of both labelled (I-2) and water as well as of the water ¹⁷O were used to construct the (I-2)-water phase diagram and to characterize the various mesophases. It is found that both M and M_F are uniaxial with negative birefringence and negative anisotropic magnetic susceptibility. The M_F phase readily aligns in a magnetic field and is characterized by fast (∼ 10⁷ s⁻¹) reorientation of the mesogen molecules about the director. The M phase is apparently columnar, highly ordered and is not readily aligned by a magnetic field. The rate of molecular reorientation in this mesophase is much slower (∼ 10³ s⁻¹) compared with M_F .