Synthesis and Rapid Characterization
of Amine-Functionalized
Silica
- Publication date
- Publisher
Abstract
Amine-functionalized colloidal silica finds use in a
variety of
applications and fundamental investigations. To explore convenient
methods of synthesis and characterization of research-grade materials
in relatively large quantities, nearly monodisperse colloidal silica
particles were prepared by base-catalyzed hydrolysis of reagent-grade
tetraethyl orthosilicate (TEOS) without the traditional time- and
energy-consuming distillation step. Radius was varied reliably from
30 to 125 nm by changing the water/TEOS ratio. Asymmetric flow field
flow fractionation (AF4) methods with online light scattering detection
proved effective in assessing the uniformity of the various preparations.
Even highly uniform commercial standards were resolved by AF4. The
surface of the colloidal silica was decorated with amino groups using
(3-aminopropyl) trimethoxysilane and spacer methyl groups from methyl-trimethoxysilane.
The surface density of amino groups was quantified spectrophotometrically
after reaction with ninhydrin; the nature of this analysis avoids
interference from sample turbidity. As an alternative to the ninhydrin
test, an empirical relationship between surface density of amino groups
and zeta potential at low pH was found. The size of the colloidal
silica was predictably decreased by etching with HF; this method will
be effective for some preparations, despite a modest reduction in
size uniformity