W0061

Characterization of Multi-Phase Aerogels by Contrast-Matched Small-Angle Neutron Scattering. C. I. Merzbacher, Naval Research Laboratory, Washington, DC 20375

Contrast-matched small-angle neutron scattering (SANS) has been used to study aerogels, a class of nanostructured materials with extremely high porosities, which are often amorphous or poorly crystalline. Aerogels are typically prepared by synthesizing a sol-gel with a large liquid fraction and then removing the liquid from the pores under supercritical conditions to prevent pore collapse.

Contrast-matched SANS is a powerful tool for the structural characterization, on the scale of 2 to 100 nm, of porous materials with two solid phases. By filling the pores with a D₂O + H₂O mixture that matches the neutron scattering length density of one phase, it is possible to observe scattering solely from the second phase. Contrast-matched SANS has been used to investigate the structure of various multi-phase aerogels, including those described below.

Ru-Ti oxide aerogels were prepared by mixing metal alkoxide precursor solutions, followed by gelation, supercritical drying and annealing at >350 ºC in various atmospheres. Although intimately mixed in the solution phase, the resulting material consists of distinct Ru oxide and Ti oxide phases. The structure depends more strongly on annealing temperature than atmosphere.

Metal oxides have been deposited in the pores of silica aerogels by vapor phase or liquid phase infiltration, followed by reduction and oxidation. Ru oxide tends to form as particles, which coarsen with increasing annealing temperature. Iron oxide forms a conformal layer with a structure that mirrors that of the silica aerogel substrate.

Composites of silica aerogel and 5 nm - 100 nm gold colloids have been prepared by mixing Au colloid with a silica sol, prior to gelation. The effect on the silica structure due to the presence of the Au was determined by filling the pores with a Au-matching D₂O+H₂O mixture.

This work was supported in part by ONR, DARPA and the NSF under Agreement No. DMR-943101.