COLL 402 |
| Heinz Hoffmann, Physical Chemistry I, Physical Chemistry I, University of Bayreuth, 95440 Bayreuth, Germany |
| Adsorption isotherms of surfactants, blockcopolymers, dyes, watersoluble polymers and proteins adsorbed on clays can be determined via surface tension measurements. We did electric birefringence and dichroism measurements on such systems to elucidate the influence of adsorption on the electric birefringence anomaly. The concentration of clay particles was adjusted such that the solutions showed large, anomalous signals. Under these conditions two birefringence or dichroism processes were induced by a rectangular electric field (E) pulse. The two processes have different signs and somewhat different rates. The faster process (FP) is due to alignment of the clay particles parallel to E while in the second process (SP) they align perpendicular. During SP, the clay particles act as apparent permanent dipoles. With increasing adsorption the amplitude of SP disappeared at saturation while FP was little effected. Disappearance of SP is due to slowing down of the mobility of condensed counter-ions by the adsorbed molecules. |
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Colloidal and Molecular Electro-Optics
Division of Colloid and Surface Chemistry |