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The purpose of this paper is to investigate the effect of various alkali-metal chloride electrolytes on the micellar formation process of Triton X-100. We have studied the micellar solutions by using static and dynamic light scattering. A combined analysis of the data obtained from both techniques has been carried out in the context of micellar structure and hydration. To examine the effect of the size and hydration of ions on the micellar growth, experiments with three different electrolytes (LiCl, NaCl, and CsCl) covering a wide range of ionic strength (0-2 M salt added) have been performed. It was found that both the ionic strength and the cation nature have a substantial effect on the micellar growth. The postulated growth mechanism consists of a progressive process involving both an increase in the micellar aggregation number accompanied with a rise of associated water which is nonspecifically bonded with the micelle. However, the amount of water molecules hydrogen bonded was found to decrease with the electrolyte addition. This mechanism is supported by the observed tendencies in both the partial specific volume and the cloud point of the surfactant for each added electrolyte.

Micellar properties of p-tert-octyl-phenoxy (9.5) polyethylene ether (Triton X-100) in aqueous mixtures of ethylene glycol (EG) were determined using such techniques as surface tension, static and dynamic light scattering, and fluorescence spectroscopy. Thermodynamics of micellization was obtained from the temperature dependence of critical micelle concentration values. The differences in the Gibbs energies of micellization of Triton X-100 between water and binary solvent systems were calculated to evaluate the influence of cosolvent on the micellization process. From this study, it can be concluded that the structure-breaking ability of EG and its interaction with the oxyethylene groups of the surfactant are dominating factors in the micellization process. Thermodynamics of adsorption of the solution−air interface was also evaluated. It was found that the surface activity of the surfactant decreases slightly with increasing concentration of EG at a given temperature. By a combination of static and dynamic light scattering measurements, a reduction of the micelle size was observed, mainly due to a decrease of the micellar aggregation number, whereas the micellar solvation was not substantially modified in magnitude with EG addition. However, the change of the surface area per headgroup of the surfactant suggested an alteration in the nature of its solvation layer, produced probably by a certain participation of cosolvent in the micellar solvation layer. This point was corroborated from the fluorescence polarization studies of several luminescent probes, including coumarin 6, merocyanine 540, and rhodamine B. These experiments revealed a slight increase of the micellar microviscosity. Finally, the proposed mechanism was also supported by the increase observed in the cloud point of Triton X-100, induced by the EG addition.

Silica is a very interesting system that has been thoroughly studied in the last decades. One of the most outstanding characteristics of silica suspensions is their stability in solutions at high salt concentrations. In addition to that, measurements of direct-interaction forces between silica surfaces, obtained by different authors by means of surface force apparatus or atomic force microscope (AFM), reveal the existence of a strong repulsive interaction at short distances (below 2 nm) that decays exponentially. These results cannot be explained in terms of the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, which only considers two types of forces: the electrical double-layer repulsion and the London-van der Waals attraction. Although there is a controversy about the origin of the short-range repulsive force, the existence of a structured layer of water molecules at the silica surface is the most accepted explanation for it. The overlap of structured water layers of different surfaces leads to repulsive forces, which are known as hydration forces. This assumption is based on the very hydrophilic nature of silica. Different theories have been developed in order to reproduce the exponentially decaying behavior (as a function of the separation distance) of the hydration forces. Different mechanisms for the formation of the structured water layer around the silica surfaces are considered by each theory. By the aid of an AFM and the colloid probe technique, the interaction forces between silica surfaces have been measured directly at different pH values and salt concentrations. The results confirm the presence of the short-range repulsion at any experimental condition (even at high salt concentration). A comparison between the experimental data and theoretical fits obtained from different theories has been performed in order to elucidate the nature of this non-DLVO repulsive force.

The classical theory of colloidal stability, the well-known Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, predicts a loss of stabilization with increasing salt concentration. An anomalous stability of the system is found at high salt concentrations when proteins cover colloidal particles. It has been demonstrated that this "non-DLVO" stability only takes place on hydrophilic systems and hydration forces are responsible for this phenomenon. In this work, different proteins (IgG, fibrinogen, myoglobin, and serum albumin) have been adsorbed onto a chloromethylstyrene (CMS) latex. The influence of the protein nature on the non-DLVO stabilization has been studied. This anomalous stabilization mechanism caused by hydration forces has been observed for all the studied proteins, although some experimental results (e.g., the critical stabilization concentration) vary for different proteins and degrees of coverage. In addition, we have shown that the orientation of the protein molecules immobilized on the CMS surface is different depending on the adsorption pH. At low pH values, when protein and polymer surfaces have different signs of charge, the macromolecules are adsorbed with a preferential orientation which differs from that obtained at higher pH values. This has been corroborated by both stability and immunoreactivity studies. Finally, we have also observed that proteins are in a dynamic state when they are adsorbed on the CMS surface. After a long time, the macromolecules tend to expose their hydrophilic areas to the aqueous medium and to hide their hydrophobic zones from solution.