Application of SIMS to the Study of Polycation Adsorption on Kaolin
Secondary Ion Mass Spectrometry (SIMS) is used to study polycation adsorption behavior on hydrophilic, negatively charged aluminosilicate surfaces. In the SIMS experiment, bombardment of a sample surface by energetic particles gives rise to a population of charged atoms, molecules, and molecular fragments. These so-called secondary ions are extracted and focused into a mass spectrometer where they are separated and identified according to their mass to charge ratio. Because the secondary ions are sputter desorbed from the uppermost surface layers of the sample, recording their mass spectra affords a sensitive probe of surface composition.
We used SIMS to study kaolin surfaces after polycation adsorptions from 0.0 and 0.1 M NaC1 aqueous solutions. When the secondary ions characteristic of the kaolin matrix and the polycation are monitored as a function of sputtering time, we observe behavior that is dependent on the adsorption conditions. For equal adsorption densities, secondary ions from matrix alu?minium are delayed relative to those from the poly-cation for the zero ionic strength adsorption case, whereas the two signals appear simultaneously when the polycation is adsorbed from 0.1 M NaCl. This suggests the polymer occupies less surface area per molecule when adsorbed from the NaCl solution, consistent with models predicting a coiled polymer configuration under these conditions.
KeywordsPolymer Adsorption Kaolin Sample Uppermost Surface Layer Atan Beam Kaolin Surface
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