Monodisperse Magnetic Silica Hexapods

A simple yet versatile
solution-based process to produce colloidal
silica hexapods is developed in which various shapes of silica rods
are grown on the faces of cubes in a controlled manner. In the presence
of hematite cubic particles, water droplets nucleate on the surface
of hematite by phase separation in pentanol. By adjusting the water
concentration, six droplets can form on each face of the hematite
cube. A silica precursor is then administered into the system, which
gradually diffuses into the water droplets through the oil phase.
Within the droplets, hydrolysis and condensation of the precursors
take place, leading to formation of silica rods. As a result, silica
hexapods on a magnetic hematite cubic seed are produced. Furthermore,
when the emulsions are aged at 60 °C prior to the silica growth,
the water content in the solution decreases gradually due to evaporation
and spiky sharp hexapods are produced. On the other hand, when organosilane
precursor is added, pancake-like hexapods are formed due to the reduction
of interfacial tension. These colloidal hexapods can further be utilized
as new building blocks for self-assembly to construct functional materials
or as a model system to understand collective behaviors.