title: Nuclear magnetic resonance studies of resorcinol-formaldehyde aerogels.
abstract: In this article, we report a detailed study of resorcinol-formaldehyde (RF) aerogels prepared under different processing conditions, [resorcinol]/[catalyst] (R/C) ratios in the starting sol-gel solutions, using continuous flow hyperpolarized (129)Xe NMR in combination with solid-state (13)C and two-dimensional wide-line separation (2D-WISE) NMR techniques. The degree of polymerization and the mobility of the cross-linking functional groups in RF aerogels are examined and correlated with the R/C ratios. The origin of different adsorption regions is evaluated using both coadsorption of chloroform and 2D EXSY (129)Xe NMR. A hierarchical set of Xe exchange processes in RF aerogels is found using 2D EXSY (129)Xe NMR. The exchange of Xe gas follows the sequence (from fastest to slowest): mesopores with free gas, gas in meso- and micropores, free gas with micropores, and, finally, among micropore sites. The volume-to-surface-area (V(g)/S) ratios for aerogels are measured for the first time without the use of geometric models. The V(g)/S parameter, which is related both to the geometry and the interconnectivity of the pore space, has been found to correlate strongly with the R/C ratio and exhibits an unusually large span: an increase in the R/C ratio from 50 to 500 results in about a 5-fold rise in V(g)/S.
authors.affiliation: Steacie Institute for Molecular Sciences, National Research Council, Ottawa, Ontario, Canada K1A 0R6.
authors.forename: Igor L
authors.initials: IL
authors.lastname: Moudrakovski
authors.forename: Christopher I
authors.initials: CI
authors.lastname: Ratcliffe
authors.forename: John A
authors.initials: JA
authors.lastname: Ripmeester
authors.forename: Li-Qiong
authors.initials: LQ
authors.lastname: Wang
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Exarhos
authors.forename: Theodore F
authors.initials: TF
authors.lastname: Baumann
authors.forename: Joe H
authors.initials: JH
authors.lastname: Satcher