ABSTRACT
In the present study, a poly(isoprene-block-dimethylamino ethyl methacrylate) diblock copolymer (PI-b-PDMAEMA) is used to structure-direct a polysilazane pre-ceramic polymer, commercially known as Ceraset. To the polymer was added a 2-fold excess in weight of the silazane oligomer (Ceraset). The resulting composite was cast into films, and after cooperative self-assembly of block copolymer and Ceraset, the structure was permanently set in the hexagonal columnar morphology, as evidenced by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Cross-linking of the silazane oligomer was achieved with a radical initiator at 120 degrees C. Upon heating of the composite to 1500 degrees C under nitrogen, the structure is preserved and a mesoporous ceramic material is obtained, as demonstrated by SAXS and TEM. The pores are open and accessible, as evidenced by nitrogen sorption/desorption measurements indicating a surface area of about 51 m2 g-1 and a pore diameter of 13 nm, consistent with TEM analysis. These results suggest that the use of block copolymer mesophases may provide a simple, easily controlled pathway for the preparation of various high-temperature ceramic mesostructures.
ABSTRACT
In the present study poly(isoprene-block-ethylene oxide), PI-b-PEO, block copolymers are used to structure iron oxide and silica precursors into reverse mesophases, which upon dissolution of the organic matrix lead to well-defined nanoparticles of spheres, cylinders, and plates based on the original structure of the mesophase prepared. The hybrid mesophases with sphere, cylinder, and lamellar morphologies containing the inorganic components in the minority phases are characterized through a combination of small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). After heat treatments the respective nanoparticles on mica surfaces are characterized by scanning force microscopy (SFM). X-ray diffraction (XRD) and superconducting quantum interference device (SQUID) magnetometer measurements are performed to demonstrate that the heat treatment leads to the formation of a magnetic gamma-Fe2O3 crystalline phase within the amorphous aluminosilicate. The results pave the way to functional, i.e., magnetic nanoparticles where the size, shape, and iron oxide concentration can be controlled opening a range of possible applications.
