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Hemimicelle formation

Hemicyanine dyes, 9 257 Hemihedrite, 6 471t Hemiisotactic micro structures, 16 108 4,6-Hemiketals, 24 595 Hemimicelle formation, 24 142 Hemins, 14 552... [Pg.426]

Chandar, S., D. W. Fuerstenau, and D. Stigler, On hemimicelle formation at oxide/water interfaces . In Adsorption from Solution, R. H. Ottewill, Ed., Academic Press, London, 1983, pp. 197-210. [Pg.1219]

Region 2 is characterized by a marked change in the slope of the adsorption isotherms. This results from the onset of association of the hydrocarbon chains of the surfactant ions adsorbed in the Stem plane. The mean separation distance of adsorbed ions under these conditions is about 70 A., which approximates the mean separation distance in bulk at the c.m.c. In such adsorption phenomena, there is a relationship between this asociation and the formation of micelles in bulk solution. For example, electrokinetic studies (1) on quartz at neutral pH showed that alkylammonium ions associate in the Stem plane when their bulk concentration is approximately one hundredth of the c.m.c. This association which has been called hemimicelle formation (3), gives rise to a specific adsorption potential which causes the adsorption to increase markedly and brings about a reversal in the sign of the potential at the Stem plane. The hemimicelle concentration, that is the bulk concentration necessary... [Pg.175]

Organic adsorbates that are more hydrophobic exhibit different adsorption behavior, particularly at higher concentrations. Long-chain fatty acids adsorb to oxide surfaces in part through surface complexation, as shown by electron spin resonance spectroscopy (32). At higher concentrations at the surface, however, favorable interactions between sorbed molecules (hemimicelle formation) appear to dominate and result in greater than monolayer adsorption (40, 41). Because humic substances (like the fatty acids) are amphiphilic, both surface complexation and hydrophobic interactions may be involved in the adsorption of humic substances on oxide surfaces. [Pg.98]

Mpandou, A. and Siffert, B., Sodium carboxylate adsorption onto TiOj Shortest chain length allowing hemimicelle formation and shear plane position in the electric double layer,./. Colloid Intel/. Sci., 102, 138, 1984. [Pg.913]

A more plausible explanation for anionic surfactant adsorption on silica gel is found in the presence of about 0.2 wt.% alumina in the silica gel. The alumina pz-c is about pH=8.0, so it would be positively charged at the pH of the experiments. If the alumina is uniformly distributed through the silica, all of the adsorption could be accounted for provided a close-packed mono-layer of surfactant is formed on the alumina. This circumstance would also be consistent with the shape of the toe of the isotherm. Gaudin and Fuerstenau (25) advanced the idea of hemimicelle formation (two-dimensional micelles on a surface) to account for similar observations in flotation processes. [Pg.20]

Information is obtained by modeling the competition between surfactant ions and other ions for adsorption sites on the floe surface. A statistical mechanical approach, as previously employed for couperative surface phasomena (e.g., hemimicelle formation), allows one to observe diet excessive concentrations of surfactant interfere with the flotation of paniculate material. This apparently results from the formation of a second bemimicelle of condensed surfactant on lop of the first, with the surfactant polar or ionic heads presented to the water this results in a hydrophilic surface (Fig. 17.2-4). The effects or ionic strength and surfactant hydrocarbon chain length on this behavior heve been modeled malhemeticaliy. [Pg.813]

Cationic surfactants strongly bind to the soil particles. As the surfactant concentration increases, hemimicelle formation on the sorbed surface cause charge reversal, which may eventually result in a reverse EOF (Li and Gale, 1996 Kaneta, Tanaka, and Taga, 1993). The problem of using cationic surfactants in electrokinetic... [Pg.243]

It is sometimes found convenient to designate two subclasses of liquid films—liquid-expanded (Li) and liquid condensed (L2)—based on subtle differences in respective ti-A curves. The Li curve is one which typically extrapolates to a limiting value of is (sometimes zero) at a molecular area of about 0.5 nm. In contrast to the bulk liquid analog, such films exhibit a significant degree of compressibility but show no signs of island or hemimicelle formation that is, it appears to maintain the characteristics of a uniform phase. In many cases, Li films show a transition to a gaseous film at low pressures and perhaps to an L2 film as the available area per molecule is decreased. [Pg.165]

The following mechanism was put forward [31] to explain this autocatalysis (1) permeation by cosurfactant (amide) of the water-AOT-toluene interfacial regions as a result of partitioning equilibria with concomitant increase in polarity and dielectric constant in these regions (2) diffusion of swollen micelle to proximity of electrode surface (3) collision of swollen micelle with the electrode surface (de facto hemimicelle formation) or with a hemi-micelle on the electrode surface and diffusion of amide through the AOT interfacial region within the electron transfer distance of the electrode (4) irreversible oxidation of amide. [Pg.169]

Hence, the slope of the logioCe versus n plot is ( )/2.3 kT, and from the data a value of of 1.1 kT was obtained, somewhat higher than the value for the free energy of micelle formation of this type of surfactant, but close to the value for hemimicelle formation on oppositely charged mineral solids (179). [Pg.181]

Despite the role of electrostatic interactions, these results also note the importance of cooperative effects of both the water structure and surfactant hemimicelle formation at the interface (Figure 10). [Pg.2728]

Measurement of interaction with protein. ) Measurement of rotational correlation time in H2O, dodecane, and solutions of sodium dodecyl sulfate and other surfactants. Measurement of rotational correlation times in starch solution at several temperatures. Measurement of rotational correlation times. ) Measurement in phosphatidyl choline vesicle membranes. Several related radicals also used. ) Measurement of effect of temperature on line broadening. Rotational correlation time measured in solutions of sodium dodecyl sulfate. ) Measurement of hemimicelle formation of surfactant SDS adsorbed onto alumina. ) Measurements in phase V liquid crystal solvents 7 other related radicals measured. 86Szal, 83Brol ), 87Bag2 )... [Pg.316]

The adsorption isotherm for the quartz adsorbent shows a bilayer character. The fitted value of the first plateau of the isotherm corresponds to the close-packed monolayer coverage, with an area of 0.3 nm occupied by one HDP. It may be concluded from the amount adsorbed at the second plateau that further adsorption of the surfactant occurs in at least two additional layers, or rather via surface hemimicelle formation. [Pg.84]

The adsorption of DDA on Silicagel R and precipitated silica powder (Fig. 3) was investigated at concentrations lower than 1 mmol/dm, i.e., well below its CMC (14.8 mmol/dm [38]). The adsorption isotherms show constant adsorption above the equilibrium concentration of 0.6 mmol/dm. The amount of DDA adsorbed is lower than that of HDP by one order of magnitude for both substrates. DDA is dissolved at low pH, and therefore the acidity of the systems was adjusted to pH 2 with HCl solution. In such an acidic medium, the surface of the adsorbents is weakly positively charged [15]. In spite of this, the adsorption of cationic surfactants occurs to a small degree. The occurrence of the second step of the isotherm for the precipitated silica can be explained in terms of the second layer or surface hemimicelle formation. [Pg.85]

FIGURE 1.6 Hemimicelle formation on solid surface, where n is the total number of monomers (surfactant molecules), and N is the aggregation number of the hemimicelle. [Pg.56]

Hemimicelle Figure 7.4. Hemimicelle formation along a polymer chain. [Pg.231]


See other pages where Hemimicelle formation is mentioned: [Pg.2600]    [Pg.581]    [Pg.165]    [Pg.439]    [Pg.440]    [Pg.176]    [Pg.118]    [Pg.124]    [Pg.511]    [Pg.313]    [Pg.47]    [Pg.52]    [Pg.22]    [Pg.2600]    [Pg.2601]    [Pg.208]    [Pg.4]    [Pg.672]    [Pg.191]    [Pg.406]    [Pg.82]    [Pg.90]    [Pg.55]    [Pg.56]    [Pg.57]   
See also in sourсe #XX -- [ Pg.41 , Pg.47 ]

See also in sourсe #XX -- [ Pg.12 ]

See also in sourсe #XX -- [ Pg.191 ]




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