Surfactants solid-liquid systems

For the solid-liquid system changes of the state of interface on formation of surfactant adsorption layers are of special importance with respect to application aspects. When a liquid is in contact with a solid and surfactant is added, the solid-liquid interface tension will be reduced by the formation of a new solid-liquid interface created by adsorption of surfactant. This influences the wetting as demonstrated by the change of the contact angle between the liquid and the solid surface. The equilibrium at the three-phase contact solid-liquid-air or oil is described by the Young equation ... 

The stabilizing function of macromolecular surfactants in solid-liquid systems is exercised through protective colloid action. To be effective, they must have a strong solution affinity for hydrophobic and hydrophilic entities. In liquid-liquid systems, surfactants are more accurately called emulsifiers. The same stabilizing function is exercised in gas-liquid disperse systems where the surfactants are called foam stabilizers. 

Perhaps the most varied combinations occur in solid-liquid systems because of the variety of properties possessed by the solid phase. The most obvious property of the solid phase to affect surfactant adsorption is the hydrophilic or hydrophobic... 

Taking Simultaneous Micellizadon and Adsorption Phenomena into Consideration In the presence of an adsorbent in contact with the surfactant solution, monomers of each species will be adsorbed at the solid/ liquid interface until the dual monomer/micelle, monomer/adsorbed-phase equilibrium is reached. A simplified model for calculating these equilibria has been built for the pseudo-binary systems investigated, based on the RST theory and the following assumptions ... 

The adsorption plateaus on this solid, determined with each of the surfactants (Table II) and the individual CMC values, were used to calculate the adsorption constants input in the model. Figure 3 compares the total adsorption (sulfonate + NP 30 EO) of the pseudo-binary system investigated as a function of the initial sulfonate fraction of the mixtures under two types of conditions (1) on the powder solid, batch testing with a solid/liquid ratio, S/L = 0.25 g/cc (2) in the porous medium made from the same solid, for which this solid ratio is much higher (S/L = 4.0 g/cc). 

H.S. Hanna and P. Somasundaran, "Physico-Chemical Aspects of Adsorption at Solid/Liquid Interfaces, Part II. Berea Sandstond/Mahogony Sulfonate System", in Improved Oil Recovery by Surfactants and Polymer Flooding, D.O. Shah and R.S. Schecter, eds.. Academic Press, 1977, p. 253-274. 

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. 

The atoms and molecules at the interface between a liquid (or solid) and a vacuum are attracted more strongly toward the interior than toward the vacuum. The material parameter used to characterize this imbalance is the interfacial eneigy density y, usually called surface tension. It is highest for metals (<1 J/m2) (1 J/m2 = N/m), moderate for metal oxides (<0.1 J /m2), and lowest for hydrocarbons and fluorocarbons (0.02 J/m2 minimum) (4). The International Standards Oiganization describes well-established methods for determining surface tension, eg, ISO 304 for liquids containing surfactants and ISO 6889 for two-liquid systems containing surfactants. 

As described above, microemulsions feature the disadvantage that the reaction product can be separated only with difficulty from other components of the system. This disadvantage can be compensated by employing highly viscous to solid liquid-crystalline phases which consist of the same components as microemulsions (oil, surfactant, water). Many enzymes display activity in several phases of a three-component mixture (Figure 12.6) (Martinek, 1986). 

This chapter reviews the wide range of colloidal systems amenable to investigation by FT - IR spectroscopy. Molecular level information about die interactions of amphiphilic substances in aggregates such as micelles, bilayers, and gels can be obtained and related to the appearance and stability of the various phases exhibited. The interactions of polymers, surfactants and proteins with interfaces, which substantially modify the solid - liquid or liquid - air interface in many important industrial and natural processes, can also be monitored using FT - IR. 

Assemblies formed by the coadsorption of surfactants at the solid-liquid interface represent attractive model systems for probing the nature and strength of lateral interactions among surfactants. These studies reveal strong synergistic effects in... 

The formation of multilayer structure can be carried out by several ways 1) adsorption on liquid/liquid interface - Langmuir-Blodgett films [5,6] 2) adsorption on solid/liquid interface - alternate adsorption of oppositely charged polyelectrolytes (PE) and surfactants on flat surfaces or spherical particles [7,8], To control the process of multilayer systems formation, it is necessary to under-... 

Two theoretical techniques worthy of serious review here, perturbation and Green function methods, can be considered complementary. Perturbation methods can be employed in systems which deviate only slightly from regular shape (mostly from planar geometry, but also from other geometries). However, they can be used to treat both linear and nonlinear PB problems. Green function methods on the other hand are applicable to systems of arbitrary irregularity but are limited to low surface potential surfaces for which the use of the linear PB equation is permitted. Both methods are discussed here with reference to surfactant solutions which are a potentially rich source of nonideal surfaces whether these be solid-liquid interfaces with adsorbed surfactants or whether surfactant self-assembly itself creates the interface. 

Emulsion systems can be considered a subcategory of lyophobic colloids. Like solid-liquid dispersions, their preparation requires an energy input, such as ultrasonication, homogenization, or high-speed stirring. The droplets formed are spherical, provided that the interfacial tension is positive and sufficiently large. Spontaneous emulsification may occur if a surfactant or surfactant system is present at a sufficient concentration to lower the interfacial tension almost to zero. 

Physical Stability of Drug Suspension. The physical stability of the non-polar drug suspensions formulated in pMDIs again depends on many parameters, such as propellant type, chemical properties of the drug compounds, and the surfactants used in the formulation. A suspension is a liquid system in which insoluble solid particles are dispersed in a liquid medium. Suspensions can be divided into colloidal suspensions, in which the... 

An amino acid, tryptophan, was dissolved in SCF ethane for the first time at the 0.1 wt.% level using AOT and octanol. Solubilities are highly adjustable in the solid-liquid-fluid region, where the partitioning of water and surfactant are variable with pressure. It is possible that this type of adjustability could be used to selectively extract and recover hydrophilic substances such as proteins. It could be used also as a means to recover surfactant for recycle, but further woik is needed to understand these complex systems. 

Particle size, shape, inter-particle forces, zeta potential, liquid surfactant phenomena, and liquid viscosity are important characteristics of a solid-liquid suspending system. Mechanism of flow through porous medium is fundamental to theories of sedimentation, filtration, centrifugation, and expression operations. Most solid-liquid materials are compacti-ble. Unique and strange behavior of pressure filtration of compactible materials has been identified. More attention should be paid for separation of those materials. 

Thomas, R.K. (1999) Neutron reflectivity at liquid-vapor, liquid-liquid and solid-liquid interfaces, in Modern Characterization Methods of Surfactant Systems (ed. B.P. Binks), Marcel Dekker, New York, pp. 417-479. 

Some essential discoveries concerning the organization of the adsorbed layer derive from the various spectroscopic measurements [38-46]. Here considerable experimental evidence is consistent with the postulate that ionic surfactants form localized aggregates on the solid surface. Microscopic properties like polarity and viscosity as well as aggregation number of such adsorbate microstructures for different regions in the adsorption isotherm of the sodium dedecyl sulfate/water/alumina system were determined by fluorescence decay (FDS) and electron spin resonance (ESR) spectroscopic methods. Two types of molecular probes incorporated in the solid-liquid interface under in situ equilibrium conditions... 

The above polymeric dispersants are essential materials for the preparation of most disperse systems, of which should be mentioned dyestuffs, paper coatings, inks, agrochemicals, pharmaceuticals, personal care products, ceramics, and detergents [1]. One of the most important applications of polymeric surfactants is in the preparation of oil-in-water (O/W) and water-in-oil (W/O) emulsions, as well as solid/liquid dispersions [2, 3]. In this case, the hydrophobic portion of the surfactant molecule should adsorb strongly at the O/W or become dissolved in... 

Fundamental investigation of the system at the molecular level. This requires investigations of the structure of the solid/liquid interface, namely the structure of the electrical double layer (for charge-stabiUsed suspensions), adsorption of surfactants, polymers and polyelectrolytes and conformation of the adsorbed layers (e.g., the adsorbed layer thickness). It is important to know how each of these parameters changes with the conditions, such as temperature, solvency of the medium for the adsorbed layers, and the effect of addition of electrolytes. 

Surfactants and microemulsion systems can be used for ex situ treatment of contaminated soil or in situ soil decontamination. In situ remediation is usually preferred if excavation of the contaminated soil is not possible or expensive, e.g. beneath buildings or for contaminations at great depth. Often bioremediation or natural attenuation is used for decontamination. In most cases, these techniques only permit the effective degradation of contaminants in the plume formed by dissolved pollutants which may be very large. However, for the remediation of a contaminated site, it is also necessary to remove the source where the pollutants maybe adsorbed in large quantities or may be present as solid or liquid phases. The latter are called NAPL (non-aqueous phase liquids) and a differentiation is made between LNAPL (light non-aqueous phase liquids) with a lower density than water and DNAPL (dense non-aqueous phase liquids) with a higher density than water (see Fig. 10.1). 

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