Reaction kinetics of molecular aggregation of rhodamine 123 in colloids with synthetic saponite nanoparticles

Abstract

The reaction kinetics of the molecular aggregation of rhodamine 123 in the colloids of synthetic saponite (Sumecton, Kunimine, Japan) was measured using a UV–Vis spectrophotometer equipped with a diode array detector with fast sampling and combined with a thermostatic stopped-flow device. The colloids exhibited a very small tendency to produce dye molecular aggregates, which can be explained by the low layer charge of saponite. Nevertheless chemometric methods, including principal component analysis and multivariate curve resolution, were able to sensitively identify spectral components. The reaction kinetics of dye aggregation followed the model, which was mathematically described by two-phase exponential functions, which indicated the presence of two parallel first-order reactions. Oblique aggregates were formed, characterized by approximate right angles between interacting transition moments. Another reaction, which was assigned to the structural changes of the aggregates, was detected after longer reaction times. The total span of the reaction was relatively low (~5%). The reaction was relatively fast, giving half-lives in the range 8–10s. Reaction kinetics parameters can be useful for the characterization of similar reactions occurring in dye/clay mineral colloidal systems.