Adhesion and Ion-Exchange between Mica Surfaces

Abstract

IF the adhesive forces between mica surfaces1 are due to ionic interactions as has been suggested2, interchange of ions between two mica surfaces brought into contact might be expected. If matching of ions and sites in the aluminosilicate lattice were complete, we should find a redistribution of the surface ions between the two faces, and if the ion-site forces were the same for any given ion with respect to both sheets, this new configuration should find half the ions from each sheet transferred to the other. Such an exchange has now been found to occur by observing the transfer of radioactive potassium-42 from a mica sheet on to which it had been exchanged from aqueous solution3 to another sheet initially inactive. When such an experiment was performed by simply pressing the two sheets of mica together on a flat surface, the amount of activity transferred was only 10 per cent of that initially present. This would suggest that the sheets were in contact over only 20 per cent of their area. This result is in line with the initial transfer values for stearic acid mono-layers between mica surfaces pressed together, as found by Rideal and Tadayon4. When the area of ntimate contact was observed by multiple-beam interference techniques, however, the amount of transfer was found to be nearly half the total exchangeable potassium in that area.