The effect of ionic aluminate and silicate species on the structure of
surfactant aggregates used in the preparation of mesoporous aluminosi
licates was investigated using dynamic light scattering and rheologica
l techniques. Aqueous cetyltrimethylammonium chloride (CTAC) solutions
saturated with sodium aluminate, sodium silicate, or tetramethylammon
ium silicate were studied over a wide range of CTAC concentrations (1.
0-2.5 wt%), which included both spherical and rod-shaped micellar regi
mes. Sodium aluminate was observed to have no effect on the structure
of CTAC micelles and so plays no role in aggregate formation in the pr
ereaction stage of the production of aluminosilicates such as MCM-41.
Silicate anions from sodium silicate and tetramethylammonium silicate
strongly affected CTAC micelle formation, promoting the formation of f
lexible wormlike micelles at dilute concentrations in which elongated
wormlike micelles are not entangled. The condensation of silicate ion
with the tetramethylammonium cation in CTAC/tetramethylammonium silica
te solution inhibited the condensation of silicate at the surface of t
he CTAC micelles. Results strongly suggest that, for the two silicate
sources studied, flexible CTAC wormlike micelles surrounded by silicat
e oligomers are formed first in the preparation of aluminosilicate mat
erials; the subsequent intermicellar condensation of silicate oligomer
s then leads to the gradual arrangement of the micelles into hexagonal
liquid crystalline arrays. The effect of a chloride ion (at a constan
t molar Cl-/CTA(+) ration of 3.98) was also investigated using sodium
chloride. Unlike the aluminate and the silicate ions, a transition bet
ween the rodlike and flexible wormlike micellar regions was observed.
The semidilute regime, defined as the concentration range over which t
he collective diffusion coefficient is described by the power law mode
l for single-chain polymer in good solvent, was observed at 11.0-21.6
wt %. The transition into the liquid crystalline regime was observed t
o begin at 21.6-25.0 wt %.