Structure of swollen polydimethyl siloxane gels

Abstract

Light and small angle neutron scattering results are presented for a series of poly (dimethyl siloxane) (PDMS) gels, cured in the dry state by endlinking with a trifunctional crosslinking agent, ethyl triacetoxy silane (ETAS). For gels swollen in octane, the scattered light and the smallest angle neutron response are dominated by scattering from aggregates of polymerized ETAS, the mean radius of which was found in this system to be ∼ 800 Å, and which have a smooth surface in the length scale between 500 and 100 Å. The internal surface area of this precipitate was roughly 200 cm2 per cm3 of the swollen gel. Only about one third of the free ETAS participates in this condensed phase. The rest is disseminated as oligomers or monomers throughout the gel. The gel itself appears as a solution-like structure with in addition permanent waves in the polymer concentration distribution. In this system, the permanent waves could be modeled by a Gaussian function of characteristic width AR = 80 Å and relative amplitude 〈Δc 2〉 1/2/〈c〉 ≈ 0.1. The polymer-polymer correlation length ξ describing the shorter range fluctuations is substantially modified in comparison with an unperturbed polymer solution at the same overall concentration. For the uncrosslinked solution at volume fraction φ = 0.16 it is found that ξ = 10.3 Å, while for the crosslinked gel swollen to the same degree, ξ = 18 Å. © 1989 American Institute of Physics.