Surfactant impurities

Alcohol sulfates are excellent foaming surfactants. According to the Kitchener and Cooper classification [148], alcohol sulfates form metastable foams. However, quantitative values cannot easily be compared because foam largely depends not only on the instrument used to produce and evaluate foam but also on the concentration of surfactant, impurities, temperature, and many other factors. In addition, a complete characterization of the foam capacity should take into account the initial amount of foam, its stability, and its texture. 

L. H. Delmau, P. V. Bonnesen, G. J. Van Berkel and B. A. Moyer, Improved performance of the alkaline-side CSEX process for cerium extraction from alkaline high-level waste obtained by characterization of the effect of surfactant impurities, ORNL/TM-1999/209, ORNL, USA, 1999. 

Delmau, L. H., Van Berkel, G. J., Bonnesen, P. V., and Moyer, B. A. Improved Performance of the Alkaline-Side CSEX Process for Cesium Extraction from Alkaline High-Level Waste Obtained by Characterization of the Effect of Surfactant Impurities, Report ORNIVTM-1999/209, Oak Ridge National Laboratory, Oak Ridge, TN, 1999. 

Colic, M. and Fuerstenau, D.W., The influence of surfactant impurities on colloid stability and dispersion of powders in aqueous suspensions, Potvder Technol., 97, 129, 1998. 

At low enough concentrations that the surfactant is totally dissolved and unassociated, the apparent equivalent conductivities of sodium 8-phenyl-n-hexadecyl-p-sulfonate ought to be about the same as the equivalent conductivities of sodium dodecyl sulfate (SDS), because they have the same cation and this ion contributes the most (around 51/71 =75%) to the conductivity. It followed that the much larger equivalent conductivities measured in samples six or more months old could be attributed neither to the surfactant alone nor to a surfactant impurity, because they did... 

A further and very efficient method of purifying aqueous surfactant solution consists in a cyclic removal of the adsorption layer. The general idea is to establish an almost equilibrium adsorption layer in which the highly surface active impurity is enriched with respect to the main surfactant. If the adsorption layer is removed, the ratio of surfactant/impurity is changed (cf. Eq. (5.6)). The idea has been realised in an apparatus which automatically performs the following steps (Lunkenheimer et al. 1987a) ... 

In the above definitions, C,yis the moiar concentration of i in the initial uniform mixture. For the desalination ratio, i is usually 2, corresponding to salt, which concentrates in region 2, whereas water concentrates in region 1 (ice in example II, Figure 1.1.2 purified water in example I, Figure 1.1.3). For the decontamination factor used with radioactive or surfactant impurities in solvents (or particles in air filtration), i is the impurity and j is the region for the purified solvent. These definitions need not be restricted to salt or a radioactive or surfactant impurity. They are... 

A most important additional aspect of such devices is that, as long as the phase interfaces are immobilized via appropriate pressure/wetting conditions, one can have a very wide range of flow rate ratios between the two phases. There is no need for any density difference between the phases. The issue of flooding does not arise, emulsification is unlikely to arise, and the need for coalescence is absent However, surfactant impurities, if present, could interfere with interface immobilization. Further, the solvents must not swell the membrane very much. Therefore the compatibility of the membrane with the solvents to be used should be checked. Smaller pore membranes will lead to a broader range of pressure difference between the two phases for nondispersive operation. The value of Kta for such devices can be larger than conventional devices by 5-50 times. 

The topic of spreading rates is of importance in the technology of the use of mono-layers for evaporation control (see Section IV-6) it is also important, in the opposite sense, in the lubrication of fine bearings, as in watches, where it is necessary that the small drop of oil remain in place and not be dissipated by spreading. Zisman and coworkers have found that spreading rates can be enhanced or reduced by the presence of small amounts of impurities in particular, strongly adsorbed surfactants can form a film over which the oil will not spread [48]. 

Barnes and co-workers have studied mixed-monolayer systems [278,281,283,284] and found some striking nonidealities. Mixed films of octadecanol and cholesterol, for example, show little evaporation resistance if only 10% cholesterol is present [278] apparently due to an uneven granular microstructure in films with cholesterol [284]. Another study of cellulose decanoate films showed no correlation between holes in the monolayer and permeation rate [285]. Polymerized surfactants make relatively poor water evaporation retarders when compared to octadecanol [286]. There are problems in obtaining reproducible values for r [287] due to impurities in the monolayer material or in the spreading solvent. 

The standard electrode potential for zinc reduction (—0.763 V) is much more cathodic than the potential for hydrogen evolution, and the two reactions proceed simultaneously, thereby reducing the electrochemical yield of zinc. Current efficiencies slightly above 90% are achieved in modem plants by careful purification of the electrolyte to bring the concentration of the most harmful impurities, eg, germanium, arsenic, and antimony, down to ca 0.01 mg/L. Addition of organic surfactants (qv) like glue, improves the quaUty of the deposit and the current efficiency. 

Increase adhesion tension. Maximize surface tension. Minimize contact angle. Alter surfactant concentration or type to maximize adhesion tension and minimize Marangoni effects. Precoat powder with wettahle monolayers, e.g., coatings or steam. Control impurity levels in particle formation. Alter crystal hahit in particle formation. Minimize surface roughness in milhng. 

The color is adversely effected mainly by impurities in the LAB. In such cases LAB is refined before sulfonation with sulfuric acid. If the neutral oil content (paraffin hydrocarbons, sulfones, and/or unsulfonated LAB) is too high, the surfactant properties of the LAB are negatively affected. In such cases, for example, the paraffins are removed prior to sulfonation by treatment with molecular sieves [152]. 

Alcohol sulfates commonly have free alcohol and electrolytes as impurities. Other hydrophobic impurities can also be present. A method suitable for the purification of surfactants has been proposed by Rosen [120]. Consequently, commercial products have CMCs that deviate from the accepted reference values. This was demonstrated by Vijayendran [121] who studied several commercial sodium lauryl sulfates of high purity. The CMC was determined both by the conductimetric method and by the surface tension method. The values found were similar for both methods but while three samples gave CMC values of 7.9, 7.8, and 7.4 mM, close to the standard range of 8.0-8.2 mM, three other samples gave values of 4.1, 3.1, and 1.7 mM. The sample with a CMC of 7.9 mM was found to have a CMC of 8.0 mM with no detectable surface tension minima after purification and recrystallization. This procedure failed in all other cases. 

The adsorption behavior of homologous sodium alcohol sulfates at the interface can be characterized by the adsorption isotherms. However, the adsorption parameters of these isotherms are very sensitive to impurities present in the surfactant. Wiinstneck et al. [145] determined the equilibrium values of... 

The types of analyses discussed in this section can be divided into two groups active matter and impurities. Several methods assess the anionic surfactant (active matter) content of the AOS product. These are particularly important since detergent performance is directly related to surfactant concentration. The different types of anionic active material are identified and quantified. 

The synthesis and surface-active properties of higher hydroxyalkanediphos-phonates are discussed in Ref. 67. Phosphorus-containing betaines as hydrolytically stable surfactants, free from alkali salt impurities, were prepared by a reaction of amidoamines and equimolar amounts of phosphonate esters with 1.5-2 eq of formaldehyde at 60-140°C in a polar solvent [72]. 

Major applications of modern TLC comprise various sample types biomedical, pharmaceutical, forensic, clinical, biological, environmental and industrial (product uniformity, impurity determination, surfactants, synthetic dyes) the technique is also frequently used in food science (some 10% of published papers) [446], Although polymer/additive analysis takes up a small share, it is apparent from deformulation schemes presented in Chapter 2 that (HP)TLC plays an appreciable role in industrial problem solving even though this is not reflected in a flood of scientific papers. TLC is not only useful for polymer additive extracts but in particular for direct separations based on dissolutions. 

Cosurfactants have not been employed in the present study. However, surfactants from commercial sources will contain isomers and manufacturing impurities. Nevertheless, a major aim of this study has been to address the performance characteristics of commercial formulations. Wherever appropriate, hydrophobic... 

Fig. 3.4. Microtiter plate UV spectra taken in in acceptor wells. The weighted residuals plots triplicate of propranolol reference, donor, and indicate that the shapes of spectra in donor acceptor solutions, at iso-pH 7.4 in 20% wt/vol and acceptor wells are in agreement with those soy lecithin in dodecane. (a) After 15 h per- in the reference wells, confirming that neither meation time, surfactant-free (b) 3 h, 35 mM decomposition nor impurities were detectable.

Increase Adhesion Tension Maximize Surface Tension Minimize Contact Angle Determine the critical surfactant concentration to maximize adhesion tension. Control impurity levels in particle formation... 

The sulphosuccinamate surfactants CA540 (Allied Chemical, USA) and 845 (Cytec) both contain four dissociable groups, three carboxylate and one sulphonate. Both collectors contain impurities such as dodecyl amine, maleic acid derivative and residual alcohols. This may explain the quite strong frothing properties of these collectors. 

---