Joseph F. Lomax

Water-associated dielectric relaxation in oxide nanoparticles

Audio frequency dielectric relaxation studies were carried out over the temperature range 120 to 390K on nanoscale mesoporous silica coated with polystyrene and nanoscale γ alumina. Two features are observed, both of which are attributed to water. A relaxation is observed at about 150K and 1000Hz that is thermally activated. The activation enthalpy is relatively high and the pre-exponential appears to be unusually low and to depend upon the water concentration. A model is presented that accounts for the apparently anomalous behaviour. This relaxation is attributed to water molecules bound at surface hydroxyl groups. A feature is found in the vicinity of 250K and 1000Hz that is associated with conductivity that varies as ω n . This response is attributed to hopping conductivity in loosely bound surface water.

Electrical relaxation of dimers in rare earth-doped calcium fluoride

Abstract Audio frequency complex impedance measurements have been carried out over the temperature range 310–510 K on samples of calcium fluoride containing 0.1 mol % of either lanthanum or cerium. Consequently, the R IV relaxation has been studied. The activation energies are found to be 1.049 and 1.089 eV for cerium and lanthanum, respectively. This relaxation is due to reorientation of a rare earth dimer. The structure of the defect site is discussed.

ELECTRICAL RELAXATION IN ULTEM® AND ULTEM® CONTAINING MESOPOROUS SILICA

Mesoporous silica has been added to Ultem® 1000 polyetherimide using solution casting. The mesoporous silica that was added was either uncoated or coated with polystyrene. Audio frequency dielectric relaxation studies were then carried out over the temperature range 5.5 to 550 K. Several interesting results were obtained. First, the uncoated mesoporous silica caused essentially no change in the relaxation spectrum of pure Ultem®. The polystyrene coated mesoporous silica caused rather large changes. The most striking example is the introduction of a new relaxation. This relaxation occurs at about 150 K and 1000 Hz as showing in fig. 1 via the open circles.

Studies in Mesoporous Silicates: Impedance Measurements on SBA-15 Loaded with Sulfonated-Polystyrene and Nafion with SBA-15 Filler

An organic-inorganic composite was formed by cross-linking polystyrene (PS) into a SBA-15-type mesoporous silica (SBA/PS). The SBA-15/PS reacted with sulfuric acid according to published methods to sulfonate the benzene rings of the styrene (SBA-15/PS/SO3). These two latter solids were investigated by TGA/MS to determine stability and decomposition mechanisms. Complex impedance measurements at 10-105 Hz were taken on (SBA-15/PS/SO3) and Nafion cast films loaded with SBA-15 at a level of 1-10%, and similar films with SBA-15/PS/SO3 in hopes that the mesoporous solids might impart desirable properties on the Nafion.