Ultra small angle neutron scattering study of the nanometer to micrometer structure of porous Vycor

Ultra small angle neutron scattering (USANS) and SANS measurements, covering length scales from nanometers to micrometers, were made to investigate the structure of monolithic porous Vycor.1 USANS from dry Vycor showed strong very low angle scattering below scattering vector q = 0.001 Å−1 while SANS showed the typical inter-pore correlation peak at q = 0.023 Å−1. When the sample was saturated with a 60/40 D2O/H2O vol/vol mixture with a neutron scattering density matched to silica framework, the inter-pore correlation peak disappeared as expected confirming that all the nanopores are interconnected. However, the very low angle scattering related to micrometer structure remained prominent even in the contrast matched liquid. The origin of the residual low q scattering is discussed.