Adsorption of surfactant molecules

Adsorption of surfactant molecules and/or of suitable coating agents at the nanoparticle surface... 

The primary mechanism for energy conservation is adsorption of surfactant molecules at various available interfaces. However, when, for instance, the water-air interface is saturated conservator may continue through other means (Figure 12.3). One such example is the crystallization or precipitation of the surfactant from solution, in other words, bulk phase separation. Another example is the formation of molecular aggregates or micelles that remain in solution as thermodynamically stable, dispersed species with properties distinct from those of an isotropic solution containing monomeric surfactant molecules (Myers, 1992). 

Adsorption of surfactants (molecules that contain a hydrophobic moiety). Interfacial tension and adsorption are intimately related through the Gibbs adsorption law its content—expressed in a simple way—is that substances that reduce surface tension become adsorbed at interfaces. 

According to Rehbinder, the structural-mechanical barrier appears due to the adsorption of surfactant molecules that are capable of forming g e 1 -1 i ke structured layer at the interface, but are not necessarily highly surface... 

Figure 12 Film-rupture by dewetting action of hydrophobic parcticle a) and by adsorption of surfactant molecules b)...

Spreading agents, adsorption of surfactant molecules, decrease of surface viscosity... 

During the adsorption of surfactant molecules on the gas-liquid interface, a monomolecular layer is formed. At low surface concentrations of the surfactant... 

The amphiphilic structure of surfactant molecules not only results in the adsorption of surfactant molecules at interfaces and the consequent alteration... 

The concept of critical micelle concentration has been introduced in Chapter 1. A look at Fig. 2.2, which is a hypothetical diagram showing breaks in measurable physical properties of a surfactant, like surface tension or density as a function of surfactant concentration in aqueous media, indicates that the sudden changes in the properties do take place at concentrations very close to each other (not exactly the same concentration - this is understandable as the deviations are generally within the limits of experimental error). Thus, a very specific, unique value of CMC may not be assigned to a surfactant when one considers the breaks in a series of properties. Rosen [3] has described this micelle formation as an alternative to simple adsorption of surfactant molecules at the water-air interface with the hydrophobic tails avoiding contact (as much as possible) with water, as in Fig. 

The adsorption of surfactant molecules at an interface decreases the interfacial tension. The decrease of the water-air interfacial tension explains the foaming property. The addition of a surfactant into a biphasic liquid system renders emulsion formation possible by the decrease of the liquid-liquid interfacial tension. Wetting and detergency are two important... 

It was shown that the adsorption of surfactant molecules on the silica surface changes its polarity. Obviously, it also changes its structure, surface area, pore volume and pore size. It was shown that, with SDS and Brij 35, the surface area lost beyond the cmc was close to 0.6 m per adsorbed surfactant pmole [16]. For example, 0.5 pmol/m of Brij 35 were adsorbed on Resolve C18 when the aqueous phase concentration was 0.02 M [16]. The initial surface area of this phase was 180 mVg. The total amount of adsorbed Brij 35 at 0.02 M is 90 pmoles. The surface area decline is close to 90x0.6 = 54 m. The surface area of the stationary phase covered by the Brij 35 layer at 0.02 M is only 126 mVg, a 30% loss. The surface area loss was only 0.3 m per adsorbed pmole of Brij 22. 

Fig. 10.2 Adsorption of surfactant molecules (black spheres) at the interface between water (white spheres) and air. The curve C qualitatively pictures the surfactant concentration as a function of the distance z from the interface shown by the dash line...

Some metallic detergents, such as sulfonates, in particular the overbased sulfonates, function as a rust inhibitor by forming a film through adsorption of surfactant molecules or neutralizing the acidic materials, preventing them from attacking the metal surfaces. Acidic materials are commonly produced by incomplete combustion of fuels or oil oxidation. 

LIGHT SCATTERING STUDY OF ADSORPTION OF SURFACTANT MOLECULES AT OIL-WATER INTERFACE... 

The adsorption of surfactant molecules at oil-water interfaces has attracted much interest, in relation to the oil recovery techniques (1). The systems containing oil, water and emulsifier molecules form generally two phases an aqueous phase containing sometimes solubilized oil in the form of small droplets surrounded by emulsifier molecules and an oil phase which also can contain solubilized water. When the amount of emulsifier is large enough, the system can form only one phase, i.e. all the water (or oil) can be solubilized in the oil (or water). The system is again a dispersion of very small droplets of water (or oil), surrounded by emulsifier molecules, in a continuous medium containing the oil (or water). Such dispersions are currently called microemulsions. The droplet size is usually of the order of lOOA (2). 

Gibbs and Insoluble Monolayers The adsorption of surfactant molecules at the surface of a liquid can be so strong that a monomolecular film (Gibbs monolayer) of unidirectionally ordered surfactants is formed (Fig. 5). Since the decrease in surface tension is directly related to the surface excess adsorption of the surfactant by the Gibbs adsorption equation (Eq. 6), the formation of the Gibbs mono-layer can be monitored by decrease of the surface tension. The maximum number of molecules filling a given area depends upon the area occupied by each molecule. 

Based on the results of our study we would assume that adsorption of surfactant molecules at hydrophobic solid/ liquid interfaces does not play a decisive role in spreading processes. 

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