The effect of added salt on the aggregation of clay particles

The spectral time evolution of Methylene Blue (MB) in SWy-1. and in Laponite aqueous clay suspensions are quite different. However, in the presence of added salts the spectral behavior in both clay suspensions becomes similar and approaches that of Laponite. The changes of the spectrum in the Laponite suspensions are due to the different MB species formed as a consequence of the approximation-association processes of the clay particles with time (aging process), whereas for SWy-1 suspensions the spectral variations are due to the migration of the dye molecules over the surfaces of the clay tactoids. The addition of salt assists the particle-particle approximation-association processes in both clays, especially in SWy-1 suspensions. Thus, the absorption spectra of MB in these conditions are altered and show peaks that are ascribed to internal dye species trapped in spaces created by the association of the clay particles. (C) 2000 Academic Press.