Mechanistic study of cationic dye interactions with clay‐polymer dispersions via metachromatic effect, aggregation, and surface charge

Abstract

Interactions for a series of aqueous dispersions of a clay, Laponite, and nonionic difunctional triblock copolymer, Pluronic L62, with two cationic dyes, crystal violet and brilliant green, are studied using UV-vis spectroscopy, dynamic light scattering (DLS), and electrophoretic mobility (EPM) to better understand the adsorption mechanisms. Different concentrations for clay, 0.1-2.0 g/L, mixed with polymer, 0.125-0.5 g/L to produce an organoclay, were tested with a fixed dye concentration, 2.0 3 10 25 mol/L. The aggregation states of the cationic dyes interacting with the clay-polymer dispersions were characterized by UV-vis absorbance. The dyes changed aggregation states from monomer to dimer and higher aggregate states upon addition to varying Laponite-polymer dispersion concentrations. DLS was used to understand the adsorbed polymer and dye interactions on the clay particle showing longer relaxation times for the largest aggregates observed from UV-vis absorbance. The EPM was used to characterize the surface charge of the clay relative to the polymer-dye interactions, which showed that the surface charge approached zero as the dyes interacted with clay-polymer dispersions. The most significant changes occurred with a reduction in light scattering intensity and longer relaxation decay at 0.1 g/L Laponite and 0.5 g/L Pluronic L62 concentrations in the presence of cationic dyes.

Supramolecular-Surface Photochemistry: Supramolecular Assembly Organized on a Clay Surface Facilitates Energy Transfer between an Encapsulated Donor and a Free Acceptor

“…A fair amount of research for photochemical energy transfer reactions has been carried out to build artificial light-harvesting systems such as supramolecular assemblies of organic molecules, covalently linked systems, and dendrimer systems. − We have focused our investigations on using clay minerals as a novel host material for guest functional dyes. ,− Saponite is a group of clay materials that are characterized by (1) nanostructured flat sheets, (2) negatively charged surfaces, (3) stack ability of individual nanosheets depending on the surrounding conditions, and (4) optical transparency in the visible region in the exfoliated state, when the particle size is small (ca. <200 nm). ,,− An advantage of this system is that it prevents an aggregation of dyes that usually happens in solution or inorganic surfaces. − Formation of a unique nonaggregated porphyrin assembly on clay surface is attributed to “size matching” of the distances between the charged sites in the porphyrin molecule and those between the anionic sites on the clay surface . By using this clay/dye complex, we have recently demonstrated nearly quantitative energy transfer between two types of dyes involving porphyrin and phthalocyanine derivatives and constructed an artificial light-harvesting model. , One limitation of this supramolecular clay/dye system is that there is no possibility to use neutral molecules such as aromatics on these surfaces.…”