Effects of Dye Surface Concentration on the Molecular Aggregation of Xanthene Dye in Colloidal Dispersions of Montmorillonite

Abstract

The molecular aggregation of organic dyes onto clay mineral particles is a very complex phenomenon including dye adsorption, the migration of dye molecules, rearrangement of initially formed aggregates, etc. Some details of this complex process are not yet fully understood. The objective of the present study was to understand the influence of dye surface concentration on the dynamic processes in dye molecular aggregation. A stopped-flow rapid mixing device was used for accurate measurements of the molecular aggregation of the cationic dye rhodamine 123 (R123) in montmorillonite (MntK) colloidal dispersions. The influence of dye surface concentration, which was changed by altering the ratio of the amount of R123 to the mass of MntK (nR123/mMntK), was examined in detail. Chemometric analysis was used to reconstruct the spectral matrix to obtain linearly uncorrelated spectral profiles of the major components and their concentrations at the respective reaction times. The conversion of isolated R123 cations into oblique J-aggregates (head-to-tail molecular assemblies) was observed over time and the existence of a J-dimers intermediate was hypothesized. The reaction kinetics followed a biphasic exponential function. An unexpected effect of dye surface concentration on R123 aggregation was observed: the initial formation of the molecular aggregates increased significantly with dye surface concentration, but an inverse trend was observed after longer reaction times. While dye aggregates were formed slowly at low dye loadings, systems with high R123/MntK ratios (nR123/mMntK) reached spectral stability after the first few seconds of the reaction. After longer reaction times, the greatest degree of dye aggregation was achieved in the dispersion of the lowest dye loading. Such a phenomenon is described for the first time. The results presented here are important for understanding the complex processes occurring in systems based on organic cations and clay minerals, and should be considered in the development of functional hybrid materials of dyes and nanoparticles with a layered structure.

Insights into Influences of Dye Hydrophobicity on Cleanliness and Resolution of Fabric Ink-Jet Printing

“…Hence, the effect of hydrophobicity on interactions between molecules in a liquid was investigated. The methods commonly used to test the dye structure are visible absorption spectra and electrical conductivity. − The two kinds of reactive dyes with a similar structure were tested by the visible absorption spectra, which directly reflected the changes of dye aggregates and single molecules. Table describes the maximum absorption peaks of visible absorption spectra of RR218 and RR24:1 solution.…”

Adsorption of Dye Molecules and Its Potential for the Development of Photoactive Hybrid Materials Based on Layered Silicates

“…While in bulk solutions the aggregation is diffusion-controlled and extremely fast, in colloidal systems it is a much slower and very complex process. Recently, it was possible to determine the exact mechanism of molecular aggregation of the cationic dye, rhodamine 123, on the surface of colloidal particles of an expandable layered silicate. , Two different types of molecular aggregates were observable in this system such as the structurally nonideal J-aggregates and the twisted H-aggregates with a sandwich-like structure. The H-aggregates were instantly formed from the adsorbed R123 monomers at the beginning of the adsorption process, but afterward they were rearranged to the more stable J-aggregates.…”

“…In addition to the changes in the properties of adsorbed dye molecules, it is also necessary to consider their impact on the properties of the colloidal systems themselves . Adsorption of organic molecules often leads to the destabilization of colloidal dispersions with subsequent particle flocculation.…”

“…A detailed analysis was carried out for colloidal systems based on layered silicate nanoparticles with adsorbed rhodamine 123 (R123) cations . The processes related to the redistribution of molecules initially adsorbed on the free surface of particles were characterized by rather complex mechanisms. , In addition to the sorbate–sorbent interactions, the processes were influenced by the bonds between the sorbate and solvent molecules, the sorbent-solvent interactions, the interactions between the colloidal particles themselves, and, finally, the interactions between the sorbate molecules. Although the redistribution of the adsorbed molecules is mainly observable for dyes, due to their specific optical properties, it is likely to be a universal process following the adsorption in a huge variety of colloidal systems.…”

“…In addition to the changes in the properties of adsorbed dye molecules, it is also necessary to consider their impact on the properties of the colloidal systems themselves. 4 Adsorption of organic molecules often leads to the destabilization of colloidal dispersions with subsequent particle flocculation. The association of the layered particles by face-to-face stacking within the larger agglomerates leads to an increase in the local concentration of the dye molecules in the interfacial region.…”