Adsorption of surfactants at the solid/liquid interfac

Dispersion properties can be modified by adsorption of surfactants at the solid-liquid interface. Surfactant adsorption can alter the dispersion properties by changing the van der Waals attraction, electrostatic repulsion, and the steric forces between the particles as discussed earlier. The extent of the modification depends on the adsorption density (surface coverage), packing and orientation of molecules at the interface, and the nature of charges on the molecule. Therefore, it is important to first discuss the adsorption process itself in terms of the dominant mechanisms and possible orientations. 

The adsorption of surfactants at the solid-liquid interface is strongly influenced by a number of factors (1) the nature of the structural groups on the solid surface— whether the surface contains highly charged sites or essentially nonpolar groupings,... 

Mechanisms of Surfactant Adsorption Theory. Adsorption of surfactant at the solid—liquid interface can take place by a number of different mechanisms. Accordingly, the free energy of adsorption (AGads) can be expressed as follows (35, 36) ... 

The third paper in this subject that we were able to retrieve is due to Biswas et al. [145]. In their introduction to the paper they said that dynamic and mechanistic aspects of adsorption of surfactants at the solid-liquid interface, particularly silica surface, were rare and quoted six papers. The most recent among them was due to Tiberg [146] in 1996. Adsorption kinetics was studied by Biswas et al. [145] using classical batch experiments. They found that the adsorption follows a two-step first-order rate equation. From the calculated rate constants they obtained the activation energies and entropies concluding that both processes are entropy controlled. 

The first reported work using SERS as probe to investigate the adsorption of surfactants at the solid-liquid interface dated from the beginning of the 1980s. In their report. Heard et al. [15] have shown that SERS spectra could be obtained even at submonolayer converge from n-alkylpyridinium bromide adsorbed at Ag colloid surfaces. Dendramis et al. [16] have studied the adsorption of cetyltrimethylammonium bromide (CTAB) on copper electrode surfaces. They were able to determine the CTAB adsorption rates from aqueous solution and observed no changes in the spectra as the concentration was varied... 

The adsorption of surfactant at the solid/liquid interface also lowers ysL- From Young s equation,... 

The adsorption of surfactants at the solid/liquid interface may be described by the Langmuir equation [9],... 

The adsorption of surfactants at the solid/liquid (S/L) interface determines their efficiency in powder wetting and dispersion. A reduction of the S/L interfacial tension by surfactant adsorption leads to a reduction of the contact angle, which in turn ensures complete wetting of the powder by the Hquid. In addition, the... 

The adsorption of surfactants on solid-liquid interfaces is at the center of interest in colloid and surface science. The nature of interactions between the solid surface, surfactant and the solution phase need to be understood to control the adsorption of surfactants. Solid surfaces in contact with aqueous solutions, especially surfaces of clays or minertils, are frequently charged and this charge generates a potential at the solid-solution interface. The adsorption of surfactants on the solid-liquid interface quite often proceeds at an interface which is electrified. Unfortunately,... 

Several interfacial aspects must be considered when dealing with agrochemical formulations (i) Both equilibrium and dynamic aspects of adsorption of surfactants at the air/liquid interface. These aspects determine spray formation (spray droplet spectrum), impaction and adhesion of droplets on leaf surfaces as well as the various wetting and spreading phenomena, (ii) Adsorption of surfactants at the oil/water interface which determines emulsion formation and their stability. This subject is also important when dealing with microemulsions, (ill) Adsorption of surfactants and polymers at the solid/liquid interface. This is important when dealing with dispersion of agrochemical powders in liquids, preparation of suspension concentrates and their stabilization. 

III. ADSORPTION PROPERTIES OF SURFACTANTS AT THE SOLID-LIQUID INTERFACE... 

Surfactants have widespread industrial and technological applications. Most of their applications in the colloidal science are related to the adsorption of them at the solid-liquid interface, and with their effect on the colloidal stability. When the surfactant is adsorbed in the appropriate amount and orientation, it can produce the aggregation or stabilization of the system. Important factors to maintain the stability of nanoparticles are electrostatic interaction, steric repulsion, interfacial tension, and viscosity of the outer phase. 

This paper describes a study of the dispersibility of Graphon (graphitized Spheron 6) in aqueous solutions of sodium dodecyl sulfate (SDS) an dodecyl trimethylammonium bromide (DTAB), and its relation to the adsorption behavior of the surfactants at the solid/liquid interface, with a view to determine the controlling process in the dispersibility of these systems. 

Surfactants also aid the comminution of the particles by bead milling, whereby adsorption of the surfactant at the solid/liquid interface and in cracks facilitates their disruption into smaller units. 

J.S. Clunie, B.T. Ingram, Adsorption of non-ionic surfactants, in Adsorption from Solution at the Solid-Liquid interface (see sec. 2.10b), p. 105. 

Adsorption from Solution at the Solid/Liquid Interface, G.D. Parfitt, C.H. Rochester, Eds., Academic Press (1983). (Contains chapters on adsorption of smEill molecules (G.D. Parfitt and C.H. Rochester), adsorption from mixtures of miscible liquids (J.E. Lane) and adsorption of non-ionic surfactants (J.S. Clunle,... 

In a detersive system containing a dilute surfactant solution and a substrate bearing a solid polar soil, the first effect is adsorption of surfactant at the soil-bath interface. This adsorption is equivalent to the formation of a thin layer of relatively concentrated surfactant solution at the interface, which is continuously renewable and can penetrate the soil phase. Osmotic flow of water and the extrusion of myelin forms follows the penetration, with ultimate formation of an equilibrium phase. This equilibrium phase may be microemulsion rather than liquid crystalline, but in any event it is fluid and flushable from the substrate surface. This phase change effect explains the detersive behavior of sucrose fatty esters in admixture with alkylarenesulfonates (117). 

Adsorption of Surfactants at the Air/Liquid, Liquid/Liquid, and Solid/Liquid Interfaces... 

Adsorption of Polymeric Surfactants at the Solid/Liquid Interface... 

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