swelling nature of montmorillonite and hectorite makes them The interactions of a pair of different cationic dyes (methylene appropriate for colloidal studies. Laponite, a synthetic clay blue and acridine orange) in the presence of dilute aqueous suspenof lithium magnesium silicate, which forms excellent colsions of the montmorillonite SWy-1 and Laponite clays were studloids in water, is also frequently used in this type of study. ied using spectrophotometric techniques. A standardized proce-The particles of this clay are significantly smaller than those dure was developed to prepare the samples and perform the specof SWy-1 when in aqueous suspensions. Also, the size of trophotometric measurements of the clay-dye suspensions. The the lamellae, as well as the number of sheets that form the observed nonadditivity of the absorption spectra of the mixture particles, are smaller than for SWy-1. It is reported that compared with those of the individual dyes is attributed to the in aqueous suspensions, Laponite particles are completely formation of mixed aggregates on the clay particles. Significant spectral variations with time were observed: for suspensions con-dispersed, not forming tactoids, so that the clay is found taining the montmorillonite SWy-1 they were mainly due to the mainly as individual sheets (3). The aging of these suspenreorganization of the dye molecules on the clay particles. For syssions leads to the aggregation of the clay particles.
tems containing Laponite, the spectral changes were ascribed to An important property of the clays is that the layers are processes of approximation-association of the clay particles. At negatively charged due to the isomorphic replacement of longer times (24 h) the association processes prevail, even for the some cations present in the clay structure by others of lower SWy-1 suspensions. After sufficient time, both the SWy-1 and the charge and similar size. This negative charge is normally Laponite suspensions showed similar spectra, indicating that the balanced by hydrated cations placed in the interlayer spaces processes occurring in both systems lead to similar configurations.
(4, 5). Cationic dyes, like those used in this work, can be Schemes are proposed to describe the temporal variations ocattracted toward the anionic layers and are, therefore, quite curring in these systems.