Surfactant adsorption amphoteric

Adsorption can be measured by direct or indirect methods. Direct methods include surface microtome method [46], foam generation method [47] and radio-labelled surfactant adsorption method [48]. These direct methods have several disadvantages. Hence, the amount of surfactant adsorbed per unit area of interface (T) at surface saturation is mostly determined by indirect methods namely surface and interfacial tension measurements along with the application of Gibbs adsorption equations (see Section 2.2.3 and Figure 2.1). Surfactant structure, presence of electrolyte, nature of non-polar liquid and temperature significantly affect the T value. The T values and the area occupied per surfactant molecule at water-air and water-hydrocarbon interfaces for several anionic, cationic, non-ionic and amphoteric surfactants can be found in Chapter 2 of [2]. 

Dependence of Adsorption, on Rock Type. Table I shows that gas injection EOR projects are being conducted in sandstone and carbonate pools. Hydrocarbon- and C02-misdble projects are run largely in carbonate reservoirs. With the exception of several studies that report adsorption levels of EOR surfactants on carbonates (4,11,12, 24, 33, 62—64, 86), the petroleum literature has dealt almost exclusively with anionic, and sometimes nonionic, surfactant adsorption on sandstones, because most studies have been carried out with surfactants used in low-tension flooding. These surfactants are not considered suitable for application in carbonate reservoirs because of their low salinity and hardness tolerance. Foam-forming surfactants suitable for high-salinity environments include amphoteric surfactants (2). The adsorption behavior of this surfactant type has also rarely been studied (10—12, 87, 88). 

Figure 20 contains adsorption levels measured in the water-wet and mixed-wet sandstones in the absence and in the presence of residual oil. Similar trends are observed for the anionic and the amphoteric surfactant. Adsorption levels in the water-wet cores are essentially the same in the absence of oil and in the presence of any of the three oils. In a water-wet system, the solid surfaces are surrounded by water films. As long as water-wet conditions prevail, the aqueous surfactant solution is in contact... 

Surfactant adsorption on the reservoir surface is another important factor to be considered when using foams in EOR processes is discussed in [258]. Adsorption experiments with surfactants of different structures were performed on cores of a number of materials (quartz, sandstones, kaolin, calcite and others), both clean and modified (impregnated) with hydrocarbons of various structure ( light oil, high-viscosity oil, asphaltenes). Minimum adsorption, as well as maximum oil recovery based was observed when using amphoteric surfactants as well as surfactant mixtures, e.g. diphenyl ether disulfonate - a-olefin sulfonate (DPES-AOS). 

The rheological characteristics of the crude oil/water interface arise from adsorption of crude oil surfactants at that interface. These surfactants are amphoteric and their adsorption at the liquid/liquid interface depends markedly on the properties of the aqueous phase. Attempts to produce model crude oil surfactants (4) showed that though the surface wetting properties of crude oils could be produced, the emulsion forming characteristics could not. We have therefore chosen to examine real crude oil/water interfaces in spite of the difficulties in interpretation that this sometimes entails ... 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

In what follows, one considers for illustration purposes the case in which the charge is generated on the surface of colloidal particles or droplets by the adsorption of a surfactant, namely sodium dodecyl sulfate (SDS). We selected this case because information about the adsorption of SDS on an interface is available in the literature, and as it will become clearer later the number of parameters involved is smaller than in the case of silica. A more complex calculation about the silica and the amphoteric latex particles will be presented in a forthcoming paper. It involves several kinds of surface dipoles and equilibrium constants. 

C02-foam mobility was reduced with all of these surfactants, although there were significant differences in the degree of mobility reduction. In particular, both anionic and nonionic surfactants were effective, as were the amphoteric surfactants. The major differences became evident when the amount of their adsorption on rock and their chemical stabilities were tested. 

Dependence of Adsorption on Temperature. Figures 11 and 12 show the temperature dependence of adsorption for several foam-forming surfactants on sandstone or unconsolidated sand. Physical adsorption is an exothermic process and is expected to decrease with increasing temperature. This trend is observed for the anionic surfactants (Figures 11a and 12) Adsorption decreases up to an order of magnitude when the temperature is raised from 50 to 150 °C. In contrast, adsorption of the amphoteric surfactants is affected very little by temperature and may even show a slight increase with temperature in some cases (Figure lib). An increase in adsorption with temperature has sometimes been taken as an indication of chemisorption (36). 

The tested amphoteric surfactants (betaine and sulfobetaine) are highly salt-tolerant and are excellent foamers. Adsorption of these surfactants is less dependent on salinity than adsorption of anionic surfactants, and the trends are not monotonic (Figure 13b). Adsorption of amphoteric surfactants may proceed by a complex interplay of mechanisms involving electrostatic and complexation mechanisms of both the cationic and the anionic group in the surfactant molecule (12, 87, 88). The trends in ad-... 

Adsorption of both amphoteric surfactants on sandstone and dolomite is significantly higher than adsorption of the anionic surfactant on these rocks. On limestone, all three surfactants exhibit intermediate adsorption levels that are quite similar among the three surfactants, particularly in sodium chloride brine. 

Figure 16. The effect of solid surface charge on adsorption of anionic and amphoteric surfactants. Key SS, Berea sandstone LS, Indiana limestone and Dolo, Baker dolomite. (Reproduced with permission from reference 12. Copyright 1992 Elsevier Science Publishers.)...

The second example involves a mixture of two different types of commercial foam-forming surfactants anionic and amphoteric (7). Unlike the mixture of the previous example, an anionic—amphoteric surfactant mixture probably does not follow ideal mixed micelle behavior (138). The results of three core-floods, performed separately with each surfactant and with a mixture of the two surfactants, are summarized as follows. The anionic surfactant adsorbs negligibly when used either by itself or when mixed with the betaine (at least at the low salinity used in these particular core-floods). Betaine adsorption is lowered by about an order of magnitude by mixing it with the anionic surfactant, from 1.7 down to 0.2 mg/g. 

Sykes and Hammes [43] have described the adsorption of both of these cationic polymers onto hair from solutions of different amphoteric and anionic surfactants. Analogous to the adsorption of polymer JR, uptake values were greater onto bleached hair than onto unbleached hair, and greater from amphoteric systems like cocobetaine or cocoamphyglycinate than from anionic surfactants like sodium lauryl sulfate or triethanolam-monium lauryl sulfate. 

Leon-Gonzalez et al.[31] proposed an FI spectrophotometric method for the determination of Triton-type non-ionic surfactants based on their reaction with alizarin fluorine blue. An on-line ion-exchange column was incorporated in the system to eliminate interferences from ionic and amphoteric surfactants. In case of interferences from non-ionic surfactants, an on-line Amberlite XAD-4 adsorption column was used to retain selectively the Triton-type surfactant, which was subsequently eluted by ethanol. However, no information was given regarding interferences from refractive index effects at the ethanol/aqueous interface and their elimination. 

All hydrocarbon mixed surfactant systems with dissimilar head groups, such as ionic/nonionic, ionic/ amphoteric, and anionic/cationic, tend to have increased adsorption relative to the pure component adsorption at the same surfactant concentration. This synergisin is analogous to the effect of mixed surfactant systems in forming low CMC surfactant mixtures. It is easier to form a mixed admicelie rather than a pure component admicelie, just as it is easier to form a mixed micelle. 

The molecular structure of surfactants controls not only the concentration of the surfactants at the interface and the resulting reduction in surface/interfacial tensions, but also affects the orientation of the molecules at the interface. The hydrophilic group is either ionic in nature or highly polar. Based on the nature of the polar group, surfactants can be classified as anionic, cationic, non-ionic or amphoteric. Among these types, anionic and non-ionic surfactants are preferably employed in enhanced oil recovery processes (EOR) due to their low adsorption on reservoir rocks. Therefore, these surfactants are briefly described. 

As pointed out above, fused silica used as a material for separation columns in capillary electrophoretic methods has normally a negative charge. Various ions, especially surfactants or big amphoteric ions, can be, however, adsorbed on the surface, which dramatically influences the zeta potential. For example, the addition of a small concentration of a suitable cationic surfactant like tetradecyltrimethylammonium bromide to the BGE causes its adsorption at the inner capillary wall and the reversal of the EOF in silica capillaries to the anodic side. Such surfactants are... 

Anionic Surfactant Blend and Amphoteric Surfactants onto Berea Sandstone, Indiana Limestone, Baker Dolomite, and Quartz. The first study to be presented examined the adsorption behavior of two amphoteric surfactants, a betaine (Empigen BT) and a sulfobetaine (Varion CAS) and a 50 50 blend of a Cio diphenyl ether disulfonate (DOWFAX 3B2), and a Ci4 i6 ot-olefm sulfonate [11]. The anionic surfactant blend was designated as DOW XS84321.05. The Cio diphenyl ether disulfonate surfactant is one isomer in a suite of surfactants which differ in their degree of alkylation and sulfonation and in their chain lengths. This suite consists of monoalkyl disulfonates (MADS), dialkyl disulfonates (DADS), monoalkyl monosulfonates (MAMS), and... 

Sarcosinate surfactants have been widely used in personal wash, skin care, and hair care formulations as coactives. They are particularly useful in providing a rich, stable lather, especially in the presence of sebum. Lathers produced from other anionic and amphoteric surfactants are remarkably enhanced by the addition of sarcosinates. Maximum foaming and detergency are developed in the pH range 4-8. The adsorption of sarcosinates onto the hair results in manageability and reduced static buildup. Sarcosinate surfactants are easily... 

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