Magnetic polymerizable surfactants: thermotropic liquid crystal behaviors and construction of nanostructured films

Abstract

Two polymerizable surfactants with different numbers of double bonds, 3-undecylene-1-vinylimidazolium bromide (C₁₁VIMBr) and 3-dodecyl-1-vinylimidazolium bromide (C₁₂VIMBr), were chosen to prepare magnetic surfactant monomers by introducing Mn²⁺, Gd³⁺ and Ho³⁺. All the surfactant monomers exhibited paramagnetism except for C₁₂VIMMn that exhibited ferromagnetism. The surface activity results indicated that the magnetic counterions tended to reduce the critical micelle concentration (cmc) and increase the dissociation constant of the surfactants, which was attributed to the stronger hydrophobicity of the magnetic anions than that of Br⁻. Compared with the surfactant monomers with Br⁻ as counterions, these magnetic surfmers showed thermotropic liquid crystal (LC) behaviors within a certain range of temperature. C₁₁VIMMn, C₁₂VIMMn and C₁₂VIMHo could form smectic A (SmA) LC phases whereas C₁₁VIMGd, C₁₁VIMHo and C₁₂VIMGd produced cubic phases with higher viscosity. The magnetic LC films with ordered nanostructures were directly obtained by in situ polymerization of the magnetic surfmers without a significant change of magnetic strength. The magnetic LC films obtained could be attracted and removed by an external magnet, providing a possibility for the development of magnetically responsive solid electrolytes and efficient adsorbents.