The effect of added salt on the aggregation of clay particles

The spectral time evolution of Methylene Blue (MB) in SWy-1. and in Laponit e 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 Laponi te 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 tac toids. The addition of salt assists the particle-particle approximation-ass ociation processes in both clays, especially in SWy-1 suspensions. Thus, th e absorption spectra of MB in these conditions are altered and show peaks t hat are ascribed to internal dye species trapped in spaces created by the a ssociation of the clay particles. (C) 2000 Academic Press.