No abstract

The structure of Nafion-117 perfluorosulfonate ionomer membranes was investigated with small-angle neutron scattering techniques. Structural changes induced by the swelling of the membranes with water, alcohols, and dipolar, aprotic solvents were monitored at solvent-swelling levels ranging from approximately 2 vol % to greater than 50 vol %. Membranes swollen up to approximately 50 vol % solvent exhibited two scattering maxima, one known to be associated with ionic regions of the membrane structure and one known to be associated with correlation distances between crystalline regions in the membrane structure. The positions of both maxima shifted toward lower scattering vector values as the solvent content in the membrane increased. The shift in the position of both maxima was linearly related to the solvent volume fraction in the membrane. The Bragg spacings corresponding to both the ionic-feature scattering maximum and the crystalline-feature scattering maximum were plotted versus the solvent volume fraction in the membranes, and the data fit with linear regression. The slopes associated with the curves of the spacing versus the solvent volume fraction were greater for the crystalline-feature spacing than for the ionic-feature spacing for all solvents other than water; this was indicative of preferential segregation of nonaqueous solvents into regions of the structure not directly associated with the ionic scattering maximum.

No abstract

Neutron reflectivity measurements on polystyrene thin films (6.5–79.0 nm thick) supported on silicon substrates indicate that the mass density is near the bulk value regardless of film thickness. To account for possible inaccuracies arising from sample misalignment, reflectivity measurements were made both from the free-surface and silicon-substrate sides of the thin film, a method termed twin reflectivity. For films spin coated on the hydrogen-terminated silicon surface the relative uncertainty in the density measurement was on the order of 1%, but for films spin coated onto the silicon native-oxide surface the analysis was more difficult because of subtleties in data fitting due to the oxide layer. Nevertheless, within the limits of greater uncertainty, these films also showed no systematic change in density with thickness.