Template-Assisted Synthesis of Janus Silica Nanobowls
- Publication date
- 2015
- Publisher
Abstract
The preparation of anisotropic nanoparticles
has drawn much attention
in the literature, with most of the efforts being dedicated to convex
particles. In this work, instead, we present a reliable method to
synthesis silica nanobowls with one well-defined opening, covering
a broad range of sizes. The nanobowls have been obtained from asymmetrically
functionalized silica–polymer Janus nanodumbbells, used as
templates, by removing of the polymer. Polystyrene seeds having different
sizes as well as surface chemistry have been used as starting material
in a two-step seeded emulsion polymerization, which leads to polymer
nanodumbbells. These dumbbells are also asymmetrically functionalized
due to the presence of silane groups on only one of their two hemispheres.
This allows us to selectively coat the silane-bearing hemisphere of
the dumbbells with a silica layer by means of a Stoeber process. The
silica nanobowls are eventually obtained after either calcination
or dissolution of the polymeric template. Depending on the route followed
to remove the polymer, nanobowls made of pure silica (from calcination)
or hybrid Janus nanobowls with a silica outer shell and a covalently
bound hydrophobic polymer layer inside the cavity (from dissolution)
could be prepared. The difference between the two types of nanobowls
has been proved by electrostatically binding oppositely charged silica
nanoparticles, which adhere selectively only on the outer silica part
of the nanobowls prepared by polymer dissolution, while they attach
both inside and outside of nanobowls prepared by calcination. We also
show that selective functionalization of the outer surface of the
Janus nanobowls from dissolution is possible. This work is one of
the first examples of concave objects bearing different functionalities
in the inner and outer parts of their surface