Neutron Scattering Investigations on a Bimodal Polymer Gel

This study investigates structural similarities in polyfluorosilicone (PFSi) gels made by different cross-linking procedures, using small-angle neutron scattering (SANS). The scattering properties of gels prepared from long and short precursor chains and of the un-cross-linked polymer solutions are reported. The gel samples were cross-linked by two methods, hydrosilylation, and condensation curing. The scattering response of a bimodal gel made by hydrosilylation is compared with that of a monomodal gel made by condensation curing having nearly identical shear moduli. Significant differences in the microscopic structure are revealed by SANS. In the bimodal gels made by hydrosilylation, the scattering spectrum can be described by two characteristic length scales, one dynamic and one static. The condensation cured sample contains in addition very large structures, possibly due to solid precipitation as a byproduct of the condensation reaction. For this system at least three correlation lengths are thus required to define the scattering curve.