Cationic High-Bulk Material

Thus a synthetic cation- (anion-) selective membrane consists of a dense polyanion (cation) matrix soaked with solvent carrying the counterions. These latter are electrostatically attracted to the fixed charges of the matrix and remain confined to it unless they are replaced by (exchanged with) some other counterions of a low molecular electrolyte dissolved in an aqueous solvent surrounding and penetrating the membrane. A porous bulk material with high counterion capacity of the type described herein is termed ion-exchanger. 

The Lattice Valency model describes a methodology based on the modification of bulk material-based RSFs (previously defined from associated reference materials), to allow for high sensitivity/detection limit quantification over interfacial region. This was put forward to account for the variability in atomic secondary ion intensities from minor and/or trace elements with the valence stale of atoms (cations) making up the substrate (Iltgen 1997). Although trends consistent with expectations are noted within the few publications available, this method does not account for sputter rate variations, nor the impact of any segregation processes, if active. 

Of particular interest for chemical transport into a predominantly smectite medium is the shrink-swell property of the clay material. The swelling properties of smectites are explained by two concepts. The first one, developed by Sposito (1973), shows that smectite swelling is caused by the hydration and mobility of the cations, which in turn balance the negative charge of the layer silicates. The second concept, presented by Low (1981), emphasizes the direct interaction of water molecules with the silicate surface. Both viewpoints fit the common observation that smectite swells in a high-hydration environment and at low electrolyte concentrations and shrinks when water is lost and salt is added to the bulk solution. 

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