Mechanisms surfactant adsorption

The mechanisms that affect heat transfer in single-phase and two-phase aqueous surfactant solutions is a conjugate problem involving the heater and liquid properties (viscosity, thermal conductivity, heat capacity, surface tension). Besides the effects of heater geometry, its surface characteristics, and wall heat flux level, the bulk concentration of surfactant and its chemistry (ionic nature and molecular weight), surface wetting, surfactant adsorption and desorption, and foaming should be considered. 

For instance, the time course of SPE demonstrates that the solvent phase surfactant concentration steadily decreases (Fig. 3) [58]. The w/o-ME solution s water content decreases at the same rate as the surfactant [58]. The protein concentration at first increases, presumably due to the occurrence of Steps 2 and 3 above, but then decreases due to the adsorption of filled w/o-MEs by the solid phase (Fig. 3) [58]. Additional evidence supporting the mechanism given above is the occurrence of a single Langmuir-type isotherm describing surfactant adsorption in the solid phase for several SPE experiments employing a given protein type (Fig. 4) [58]. Here, solid-phase protein molecules can be considered as surfactant adsorption sites. Similar adsorption isotherms occurred also for water adsorption [58]. 

The adsorption isotherm of sodium dodecyl sulfate (SDS) on alumina at pH = 6.5 in 0.1 M NaCI (Fig. 4.11a) is characteristic of anionic surfactant adsorption onto a positively charged oxide. As shown by Somasundaran and Fuerstenau (1966) and by Chandar et al. (1987), the isotherm can be divided into four regions. These authors give the following explanation for the adsorption mechanism ... 

Adsorption of a surfactant on solids is dependent, among other things, on the structure of both the hydro-phobic and hydrophilic portions of it. There are a number of mechanisms proposed for surfactant adsorption and an understanding of the effects of the structure of the surfactant can help in elucidating the role of these mechanisms. In this study, the effect on adsorption on alumina of some structure variations of sulfonates (chain length and the branching and the presence of ethyoxyl, phenyl, disulfonate and dialkyl groups) is examined above and below CMC as a function of surfactant concentration, pH and salinity. Co-operative action between an ionic alkyl sulfonate and a nonionic ethoxylated alcohol is also studied. 

Surfactant adsorption on solids from aqueous solutions plays a major role in a number of interfacial processes such as enhanced oil recovery, flotation and detergency. The adsorption mechanism in these cases is dependent upon the properties of the solid, solvent as well as the surfactant. While considerable information is available on the effect of solid properties such as surface charge and solubility, solvent properties such as pH and ionic strength (1,2,3), the role of possible structural variations of the surfactant in determining adsorption is not yet fully understood. 

The mechanism of adsorption of fatty acids and other surfactants at the oxide-water interface. J. Colloid Interface Sci. 44 407— 414... 

This overview will outline surfactant mixture properties and behavior in selected phenomena. Because of space limitations, not all of the many physical processes involving surfactant mixtures can be considered here, but some which are important and illustrative will be discussed these are micelle formation, monolayer formation, solubilization, surfactant precipitation, surfactant adsorption on solids, and cloud point Mechanisms of surfactant interaction will be as well as mathematical models which have been be useful in describing these systems,... 

A few papers have been published recently on the problem of surfactant adsorption maxima on solids in the region of the CMC (1-5). Scamehorn et al. (1,2) and Trogus et al. (3) expTTined the origin of these maxima by various radios of the surfactant solution to the solid, in connection with isomeric impurity of the surfactant. Ananthapadmanabhan and Soniasundaran (4) examined critically the presence of such maxima from the viewpoint of various proposed adsorption mechanisms. They have shown that a mechanism including micellar exclusion, mixed micelle formation and properties of solids, such as the pore size, cannot explain satisfac-... 

According to Groot (2000), the mechanism of interaction between a polymer and surfactant may be deduced by considering parameters such as polymer size, mode of surfactant adsorption (continuous or discrete micelles), and possible sites of interaction (head group or tail). For the case of the mechanism of the interaction between chitosan and sorbitan esters, the polymer concentration (dilute, semi-dilute, concentrated) of... 

Somasundaran, P., T. W. Healy, and D. W. Fuerstenau, Surfactant adsorption at the solid-liquid interface - Dependence of mechanism on chain length , J. Phys. Chem., 68, 3562-3566 (1964). 

The objective in this section is to derive a mathematical model that can be used to extract the rate of adsorption from experimentally obtained dynamic surface tension data. Various investigators have speculated that the mechanism of surfactant adsorption involves two subsequent steps ... 

Bendure indicates 10 ways to increase foam stability (1) increase bulk liquid viscosity, (2) increase surface viscosity, (3) maintain thick walls (higher liquid-to-gas ratio), (4) reduce liquid surface tension, (5) increase surface elasticity, (6) increase surface concentration, (7) reduce surfactant-adsorption rate, (8) prevent liquid evaporation, (9) avoid mechanical stresses, and (10) eliminate foam inhibitors. Obviously, the reverse of each of these actions, when possible, is a way to control and break foam. 

The first three mechanisms of surfactant adsorption have been criticized mainly because crack propagation velocities in comminution devices are often much more than the rate of adsorption of the surfactants normally used as grinding aids (20). There is considerable evidence and concurrence of opinion on the prevention of agglomeration as the mechanism of grinding aid action (21). 

Micellisation is, therefore, an alternative mechanism to adsorption by which the interfacial energy of a surfactant solution might decrease. 

The adsorption mechanism discussed in previous chapters dealt only with a monocomponent system mineral - surfactant, as a result of an adsorption equilibrium related to appropriate PDI. Since a real flotation system consists of two or more mineral components it is necessary to mention conditions of the selective surfactant adsorption in such a system. In monocomponent systems the adsorption is controlled by the character of PDI with respect to the chemical composition of the polar heads of the surfactant. However, this rule is not valid in polycomponent systems containing both kinds of PDI. Generally and under simplifying circumstances, it is possible to classify the adsorption systems according to the role played by the PDI and the kind of the mineral. 

Abstract A crucial problem in the manufacturing of high aspect ratio structures in the microchip production is the collapse of photoresist patterns caused by imbalanced capillary forces. A new concept to reduce the pattern collapse bases on the reduction of the capillary forces by adsorption of a cationic surfactant. The application of a cationic surfactant rinse step in the photolithographic process leads to a reduction of the pattern collapse. Physicochemical investigations elucidate the mechanism of surfactant adsorption... 

The behaviour of the surface tension and the contact angle allows conclusions concerning the adsorption mechanism. They are illustrated schematically in Fig. 10. At concentrations < ceff, the surfactant adsorption is driven mainly by the electrostatic attraction between the negatively charged photoresist and positively charged surfac-... 

Since the styrene series contains more surfactant than the methyl methacrylate series and since the ethyl acrylate has afforded increased surfactant adsorptivity to the styrene by a mechanism to be proposed under Question d, the equilibrium suggested by Equation 1 is shifted markedly to the left, resulting in lower requirements for carboxylate ions to achieve F/T stability. 

In this Section instability of asymmetric films is explained by decrease in the surfactant adsorption. Another reason for this instability can be the presence of solid particles at the water-oil interface. Such a heterogeneous defoaming is created when a foam is broken down by the antifoam drops that contain solid hydrophobic particles. The mechanism of action of such types of antifoams will be discussed in Section 9.4. 

The other application of pore-level mechanisms exploits their dependence on dispersion type, wettability, capillary number, and capillary pressure to design surfactants that will optimize these parameters. Measurements of phase behavior, interfacial tensions, surfactant adsorption, wettability, and related parameters will be needed to fit the various requirements of different reservoirs, each of which has a unique combination of mineralogy, pore structure, temperature, pressure, oil and brine composition, etc. 

Wilson and co-workers developed a statistical mechanical model for single component surfactant adsorption (29-31) and expanded it to a binary system (2,3). Different adsorption curves were generated by varying the Van der Waals interaction parameters. The mixed adsorption equations that were developed were very complex and were not applied to experimental data. 

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