Aluminium-Based Surfactant Mesophases Structurally and Morphologically Controlled by Anions

Abstract

Aluminium-based dodecyl sulfate mesophases were synthesized by the homogeneous precipitation from a mixture of aluminium nitrate, sodium dodecyl sulfate, urea and water with or without five kinds of additional anions. The addition of monovalent Cl^-, CH₃COO^- and HCOO^- anions yielded a hexagonal mesophase, whereas F^- anions induced a different mesophase. The crystallinities of these mesophases increased in the following order: NO₃ ^- and Cl^->CH₃ COO^->HCOO^->F^-, corresponding to the reverse order of affinity for Al³⁺. The resulting mesophases were also largely affected in morphology by the anion species added to form worm-like shaped particles for NO₃ ^- and/or Cl^- anions, and widely varying shapes of particles for the others. On calcination, these mesophases were transformed into α-alumina particles with macro pores having the specific surface area of ca. 20 m²ċg^-1. On the other hand, the addition of divalent SO₄ ^2- anions or the single use of aluminium sulfate led to a mesophase with a structural period as long as 6 nm, which was deorganized into a layered phase with an interlayer spacing of 1.4 nm.