(524d) Facile Synthesis of Silica Micro- and Nano-Rods

The use of nano-building blocks as fillers to enhance the property of composites
is a topic of great interest. The most used nano-blocks are spherical
nanoparticles, which can be prepared using a variety of methods. Nevertheless,
there is a growing interest in the use of anisotropic building blocks, such
as nanotubes, platelets, rods, ellipsoids, etc. In this work we propose a new
and reliable method for the production of large quantities of magnetic silica
micro and nano-rods. This method is based on the spinodal decomposition of a silica
precursor leading to a bicontinuous phase, the structure of which is controlled
by the incorporation of polymer-magnetite nano-spheres with the aid of an
external magnetic field. Our system is based on the silica precursor TMOS
and the polymer PEG, which undergoes a phase separation following a spinodal
decomposition due to the chemical cooling induced by the condensation
polymerization of the silica precursor. Polymer-magnetite nanoparticles are
incorporated in the silica rich phase due to the strong affinity of the magnetite
to the silica precursor. The accumulation of the nanocolloids in the silica
rich phase during the spinodal decomposition leads to the formation of long
rod-like structures in the presence of an external magnetic field, which form
a monolith. At the end of the reaction, the application of strong ultrasonication
leads to the disintegration of the monolith and to the recovery of the
rods. Different parameter such as rods diameter and length can be tuned by
varying reactant concentration, the applied magnetic field and the sonication
time. The applied magnetic field has an enormous influence on the length of
the produced rods and depending on the kind of field applied, homogeneous
or alternating, the length can be varied by more than two orders of magnitude.