Characterization of silica-polymer aerogel composites by small-angle neutron scattering and transmission electron microscopy

In this work a new type of silica-biopolymer aerogel composite containing chitosan has been studied with small-angle neutron scattering (SANS) and transmission electron microscopy (TEM). A new small-particle mass-fractal model scattering function, derived from the Teixeira mass-fractal scattering function, was used to fit the SANS data. As the content of chitosan was increased, the fractal dimension was decreased from 2.9 to 2.5, and the cut-off-length increased from 3.2 to 6.0 nm. This indicates that chitosan helps form a more open aerogel structure. It supports a structural model in which there are primary particles that connect with each other closely to form clusters, and these clusters serve as a secondary structural unit to form the chitosan-reinforced aerogel network. It also indicates that chitosan reinforces the inter-particle connections. This picture is consistent with the TEM measurements, which reveal that there are 1.5 nm wide entities with long dimensions in the 3-10 nm range.