Hydrophobicity ether sulfates

Cosurfactant requirements can be minimized usiag a surfactant having a short-branched hydrophobe or a branched-alkyl substituent on an aromatic group (232,234) and a long ethoxy group chain (234). Blends of surfactants optimized for seawater or reservoir brine salinity include linear alkyl xylene sulfonate—alcohol ether sulfate mixtures (235). 

As esters of sulfuric acid, the hydrophilic group of alcohol sulfates and alcohol ether sulfates is the sulfate ion, which is linked to the hydrophobic tail through a C-O-S bond. This bond gives the molecule a relative instability as this linkage is prone to hydrolysis in acidic media. This establishes a basic difference from other key anionic surfactants such as alkyl and alkylbenzene-sulfonates, which have a C-S bond, completely stable in all normal conditions of use. The chemical structure of these sulfate molecules partially limits their conditions of use and their application areas but nevertheless they are found undoubtedly in the widest range of application types among anionic surfactants. 

Salts of monovalent metals of alcohol and alcohol ether sulfates are soluble in water, with the solubility dependend on the cation and the chain length. Ammonium salts are more soluble than sodium salts and these are more soluble than potassium salts. On the other hand, sulfates with short hydrophobic chains are more soluble than those with longer chains but the short-chain molecules have a solubilizing effect on the more insoluble longer chain molecules [68], The solubility of sodium salts of different alcohol sulfates is shown in Fig. 2 and the solubility of sodium and potassium salts of dodecyl sulfate is compared. 

Several variations in chemical constitution, which lead to a depression of the Krafft-Point (for example, branching of the hydrophobic part of the molecule), frequently result in diminished hydrophobicity of the molecule. At constant molecular weight, the critical micelle concentration (Cj.) is shifted with increased branching to higher concentrations, the surface activity diminishes, the tendency to adsorb at hydrophobic interfaces decreases, etc. (j, 14, 15). Therefore, the nature of the oxyethylene groups in aTkyl ether sulfates is of major importance. 

Therefore, the hypothesis of an increasing nonionic character of alkyl ether sulfates with increasing number of oxyethylene groups is not tenable. Some time ago (30), it was suggested that a certain hydrophobic nature can be attributed to the polyoxyethylene chain of alkyl ether sulfates. At first, this appears to be in contradiction to the decidedly hydrophilic character of the polyoxyethylene chain for nonionic surfactants. However, the possibility of EO group hydration impairment by the sulfate group cannot be excluded. 

Table III shows some data regarding the possible hydrophobic nature of ether sulfates. From several investigations, it is known that, for nonionic surfactants with identical hydrophobic groups, an increase in the hydrophilic part of the molecule causes a decrease in the aggregation number (28). This is caused by the...

Washing and Cleaning Action. The properties of alkyl ether sulfates, due to the good solubility and the special hydrophilic/hydrophobic properties of the molecule, are of particular practical interest. From the investigations described in sections 2 and 3, it can be concluded that, in addition to the decrease in the Krafft Point, favorable properties for practical applications can be expected as a result of the inclusion of the oxyethylene groups into the hydrophobic part of the molecule. As is true for other anionic surfactants, the electrical double layer will be compressed by the addition of multivalent cations. By this means, the adsorption at the interface is increased, the surface activity is raised, and, furthermore, the critical micelle concentration decreased. In the case of the alkyl ether sulfates, however these effects can be obtained without encountering undesirable salting out effects. 

Among the ionic tensides investigated were sodium alkyl sulfates with hydro-phobic chains with different lengths (C8, CIO, C12), C12-PEG-ether sulfates with 8-50 EO groups and sodium, lithium and ammonium dodecyl sulfate. For all the ionic tensides investigated, lengthening the hydrophobic chain led to a similar increase in the w-value as with non-ionic tensides. The kifl values increased both as a function of the hydrophobic chain and also with that of the hydrophilic EO-part, the nature of the counter-ion having no effect. 

Cmiously, the introduction of ethylene oxide lowers the CMC of the sulfate. Alcohol ether sulfates with 2 mol or less of ethylene oxide are weakly hydrated and methylene groups contribute to an effective increase of the hydrophobic chain. As the number of moles of ethylene oxide increases, the effect is less pronounced. Weaker electrical interactions are also expected that favor micelli-zation [18]. 

A simple method of chemical modification of cellulose was proposed by Zhdanov and coworkers [126]. This method was based on the hydrophobic mercerization of cellulose in a superbasic medium such as the dimethylsulf-oxide-solid sodium hydroxide mixture, followed by etherification or esterification. Methyl sulfate, benzyl chloride, acetic anhydride, methyl bromoacetate, triethyleneglycol ditosylate, and p-toluenesulfonyl chloride were used as the modification agents. This method simplified appreciably the preparation of acetylcellulose and methoxycarbonylmethylcellulose. Cellulose ethers can be prepared with high etherification yield, uniform substitution, and good oxidation resistance by alkalinization and alkylation of aqueous cellulose in the presence of water-miscible cyclic ethers as suspending agents [127]. 

With long-chain hydrocarbons, such as oil, where hydrophobic and hydrophilic portions of the molecule exist, surface-tension effects will be significant, and may result in foaming and possible acceleration of carryover. The alkalinity of the boiler water may saponify any fatty acids present, producing a crude soap that may foam. Soaps, sulfated oils and alcohol, sulfonated aliphatics and aroma.ics, quaternary ammonium compounds, nonionic organic ethers and esters, and various fine particles, act as emulsifiers that can increase foaming. 

The sulfopropyl and sulfobutyl ether derivatives " have been further evaluated for their complexation with testosterone and progesterone (Fig. 7). Even though increasing the DS should produce more steric hindrance to complexation, the mono, tetra, and hepta substituted sulfobutyl ether (SBEl, 4, 7) derivatives all displayed comparable binding abilities for the steroids and the strength of binding was similar to that observed for p-CD. The SBE substituent behaves similar to that proposed for the undecyl sulfate CD, however, complexation with the SBE-p-CDs involves the CD cavity, as well as the hydrophobic butyl side arms. 

Polysaccharides with Surfactant Micelles. Consider a solution of a fairly hydrophobic polysaccharide, such as a cellulose ether. The hydrophobic groups cause a weak attractive interaction, leading to a somewhat increased viscosity at low shear rates. If an anionic small-molecule surfactant is added, say SDS (sodium dodecyl sulfate), at a concentration above the CMC (critical micellization concentration), micelles are formed that interact with the polymer more specifically, one or a few polymer chains can pass through a micelle. In this way, polymer chains can be cross-linked. If now the polymer concentration c is below c (the chain overlap concentration), mainly intramolecular junctions are formed. If c > c, however, a gel results. In this manner, viscoelastic gels can be made with a modulus of the order of 10 Pa. 

HASE (hydrophobically modified alkali-swellable emulsion, discussed in Chapters 25 and 28) and HEUR thickeners are readily displaced from acrylic latex surfaces (32) by sodium dodecyl sulfate (SDS). A surface-active cellulose ether was also reported (33) to desorb from monodispersed poly(styrene) latices with SDS addition. In these studies, the relative critical micelle concentrations of the anionic surfactant and thickener appear to be more important than buffering of surface charges. 

Lower sensitivity to temperature changes is obtained if the ion-pairing agent is added to the mobile phase as a solution in a polar solvent. Typical examples are systems with silica as the solid phase and aqueous perchloric acid [46, 47] or dodecyl sulfate in methanol [48] added to the hydrophobic organic solvent dichloro-methane or diethyl ether or a mixture of these. The polar components are enriched on the silica the retention by the stationary phase is probably due to adsorbed anions in a layer of polar solvent. Eriksson and coworkers found that the retention decreased with increas-... 

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