Surface water anionic surfactant concentrations

LAS Treatability and Environmental Concentrations. The removal of LAS during sewage treatment was confirmed by monitoring studies in both the United States and Europe. Numerous studies reported anionic surfactant concentrations in surface waters measured by nonspecific analytical techniques such as methylene blue active substance (MBAS). However, the correlation between MBAS and LAS concentrations determined by spe-... 

Predicted Anionic Surfactant Concentrations in Surface Water. 

Submicroscopic, colloidal aggregates can influence chemical reactivity. Aqueous micelles are the most widely studied of these aggregates, and these micelles form spontaneously when the concentration of a surfactant (sometimes known as a detergent) exceeds the critical micelle concentration, cmc (1-3). Surfactants have apolar residues and ionic or polar head groups, and in water at surfactant concentrations not much greater than the cmc, micelles are approximately spherical and the polar or ionic head groups are at the surface in contact with water. The head groups may be cationic, (e.g., trimethylammonium), anionic, (e.g., sulfate), zwitterionic (as in carboxylate or sulfonate betaines), or nonionic. The present discussion covers the behavior of ionic and zwitterionic micelles and their effects on chemical reactivity. 

In addition to their poor solubility in water, alkyl phosphate esters and dialkyl phosphate esters are further characterized by sensitivity to water hardness [37]. A review of the preparation, properties, and uses of surface-active anionic phosphate esters prepared by the reactions of alcohols or ethoxylates with tetra-phosphoric acid or P4O10 is given in Ref. 3. The surfactant properties of alkyl phosphates have been investigated [18,186-188]. The critical micelle concentration (CMC) of the monoalkyl ester salts is only moderate see Table 6 ... 

In Fig. 2.58 (Hetsroni et al. 2001b) the dependencies of the surface tension of the various surfactants a divided on the surface tension of water ow are shown. One can see that beginning from some particular value of surfactant concentration (which depends on the kind of surfactant), the value of the relative surface tension almost does not change with further increase in the surfactant concentration. It should be emphasized that the variation of the surface tension as a function of the solution concentration shows the same behavior for anionic, non-ionic, and cationic surfactants at various temperatures. 

The surface active agents (surfactants) may be cationic, anionic or non-ionic. Surfactants commonly used are cetyltrimethyl ammonium bromide (CTABr), sodium lauryl sulphate (NaLS) and triton-X, etc. The surfactants help to lower the surface tension at the monomer-water interface and also facilitate emulsification of the monomer in water. Because of their low solubility surfactants get fully dissolved or molecularly dispersed only at low concentrations and at higher concentrations micelles are formed. The highest concentration where in all the molecules are in dispersed state is known as critical micelle concentration (CMC). The CMC values of some surfactants are listed in table below. 

Figure 8.6 Comparison of the influence of non-ionic Ci2E6 (hexaoxyethyl-ene ft-dodecyl ether) or anionic SDS (sodium dodecyl sulfate) on adsorbed amount of p-lactoglobulin at the air-water interface (0.1 wt% protein, pH = 6, ionic strength = 0.02 M, 25 °C) as determined by neutron reflectivity measurements. Protein surface concentration is plotted against the aqueous phase surfactant concentration ( ) Ci2E6 ( ) SDS. Reproduced from Dickinson (2001) with permission.

One characteristic property of surfactants is that they spontaneously aggregate in water and form well-defined structures such as spherical micelles, cylinders, bilayers, etc. (review Ref. [524]). These structures are sometimes called association colloids. The simplest and best understood of these is the micelle. To illustrate this we take one example, sodium dode-cylsulfate (SDS), and see what happens when more and more SDS is added to water. At low concentration the anionic dodecylsulfate molecules are dissolved as individual ions. Due to their hydrocarbon chains they tend to adsorb at the air-water interface, with their hydrocarbon chains oriented towards the vapor phase. The surface tension decreases strongly with increasing concentration (Fig. 3.7). At a certain concentration, the critical micelle concentration or... 

Retention study. At surfactant concentrations below CMC, micelles do not exist and, as demonstrated by Knox (12), Deming (13) and our previous works (14-15), the degree of retention was directly related to the surface charge arising from the adsorbed surfactant With both the surfactants, the retention of neutral species (toluene and caffeine) slightly decreased. When an anionic surfactant was adsorbed, the retention of negatively charged solutes (benzoate and SOBS) fell dramatically whereas the retention of cationic solutes (BTAB and CPC) increased. The reverse occured with the cationic surfactant (14). The same kind of behavior was observed with pure aqueous mobile phases, 5-95% v/v methanol-water phases and 0.1 mol/L NaCl phases. 

Measurements of forces between probe particle and sessile oil drops in water were first reported by Mulvaney et al. [54] and Snyder et al. [55], with a number of studies following by Hartley et al. [56], Aston et al. [57,58], Attard and co-workers [59-61], Nespolo et al. [62] and Dagastine et al. [63]. As an example of the types of typical forces observed between an alkane droplet and a silica probe in the presence of an anionic surfactant, refer to Figure 4.4 [63]. The general shape of the force curve is similar, at first glance, to the behaviour at rigid surfaces, but as discussed below, this is a product of changes in separation and interface deformation. Also note that at low surfactant concentrations, jump-in does occur, but with an increase in surfactant concentration (which leads to a decrease in interfacial tensions) only repulsive forces are observed. 

The surfactant-aided Lewis acid catalysis was first demonstrated in the model reaction shown in Table 13.1 [22]. While the reaction proceeded sluggishly in the presence of 10 mol% scandimn triflate (ScfOTOs) in water, a remarkable enhancement of the reactivity was observed when the reaction was carried out in the presence of 10 mol% Sc(OTf)3 in an aqueous solution of sodium dodecyl sulfate (SDS, 20 mol%, 35 mM), and the corresponding aldol adduct was obtained in high yield. It was found that the type of surfactant influenced the yield, and that Triton X-100, a non-ionic surfactant, was also effective in the aldol reaction (but required longer reaction time), while only a trace amount of the adduct was detected when using a representative cationic surfactant, cetyltrimethylammonium bromide (CTAB). The effectiveness of the anionic surfactant is attributed to high local concentration of scandium cation on the surfaces of dispersed organic phases, which are surroimded by the surfactant molecules. 

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