Surfactant mixtures, composition

When mixing two surfactants species in a SOW system, an equilibrium takes place between the oil and water phases and the interface for each species. Since the two species do not necessarily exhibit the same affinity for the interface and the oil and water bulk phases, the compositions of the surfactant mixtures at interface and in the phases might be different. For instance if a very hydrophilic species is mixed with a very lipophihc one, as often recommended in the old formulation literature, then the hydrophihc surfactant has a strong tendency to partition in water, whereas the lipophihc one would partition in the oil. In this case the surfactant mixture in water will contain a large majority of hydrophilic species, i.e., it will be very hydrophilic, whereas the oil phase will predominantly contain the hpophihc species, with the remaining adsorbing at interface. This situation in which each species actuates on its own, more or less independently of the other, has been called non-collective behavior. Since the surfactant mixture composition at interface is often the one that commands the actual property of the system, such as the interfacial tension or the stabihty of the emulsion, it is most important to know how to calculate or measure the characteristics of the mixture present at interface. Such methods will be discussed in the next section. 

This chapter presents the results of physicochemical and tribological investigations of lubricating substances composed of water and a mixture of two nonionic surfactants sorbitan monolaurate (SML) and ethoxylated sorbitan monoisostearate (ESMIS). Particular attention was paid to proper selection of surfactant mixture composition (SML/ESMIS ratio) ensuring high effectiveness in reducing friction coefficient and wear as well as seizure prevention. 

The gravity measurements of the pelobischofite and appropriate compositions detergency showed the essential increase of this parameter for pelobischofite-surfactant mixtures. Thus the washing power of pelobischofite-surfactant solutions with concentration 0,1% was 90%. Erom another hand, similar detergency of bischofite-surfactant mixtures was reached for 1% solutions only. 

Different methods are used in microemulsion formation a low-energy emulsification method by dilution of an oil surfactant mixture with water and dilution of a water-surfactant mixture with oil and mixing all the components together in the final composition. These methods involve the spontaneous formation of microemulsions and the order of ingredient addition may determine the formation of the microemulsion. Such applications have been performed with lutein and lutein esters. ... 

Mixtures of aldehydes with surfactants are active in preventing corrosion, in particular in the presence of mineral or organic acids [646]. The aldehyde may be trans-cinnamaldehyde. The surfactant may be N-dodecylpyridinium bromide or the reaction product of trimethyl-1-heptanol with ethylene oxide [645]. Such aldehyde and surfactant mixtures provide greater and more reliable corrosion inhibition than the respective compositions containing aldehydes alone. 

The implications for films cast from mixtures of enantiomers is that diagrams similar to those obtained for phase changes (i.e., melting point, etc.) versus composition for the bulk surfactant may be obtained if a film property is plotted as a function of composition. In the case of enantiomeric mixtures, these monolayer properties should be symmetric about the racemic mixture, and may help to determine whether the associations in the racemic film are homochiral, heterochiral, or ideal. Monolayers cast from non-enantiomeric chiral surfactant mixtures normally will not exhibit this feature. In addition, a systematic study of binary films cast from a mixture of chiral and achiral surfactants may help to determine the limits for chiral discrimination in monolayers doped with an achiral diluent. However, to our knowledge, there has never been any other systematic investigation of the thermodynamic, rheological and mixing properties of chiral monolayers than those reported below from this laboratory. 

These results obtained from the analyses of industrial blends proved that the identification of the constituents of the different surfactant blends in the FIA-MS and MS-MS mode can be performed successfully in a time-saving manner only using the product ion scan carried out in mixture analysis mode. The applicability of positive ionisation either using FIA-MS for screening and MS-MS for the identification of these surfactants was evaluated after the blends examined before were mixed resulting in a complex surfactant mixture (cf. Fig. 2.5.7(a)). Identification of selected mixture constituents known to belong to the different blends used for mixture composition was performed by applying the whole spectrum of analytical techniques provided by MS-MS such as product ion, parent ion and/or neutral loss scans. 

The explanation for this behavior is similar to that given in the preceding section for nonionic surfactant mixtures. Adding a hydrophihc anionic surfactant raises the temperature at the cloud point and other phase transitions above those for pure Ci2(EO)4. If the amount of anionic added exceeds only slightly that needed for complete solubility, the final stages of the dissolution process are slow because preferential dissolution of the anionic causes the remaining drop to rise above its cloud point and nucleate small droplets of surfactant-rich liquid. But if the amount added is sufficiently large, drop composition remains below the cloud point in spite of preferential dissolution, with the result that dissolution is fast as with pure nonionic surfactants below their cloud points. 

If the mixing is followed (as for ionic surfactants) by carrying out a salinity scan, the aspect of the In S -mixture composition rule is often found to be non-linear as indicated in Fig. 13 left plot. 

Fig. 15 CMC of anionic-cationic surfactant mixtures as a function of composition of the mixture...

As the temperature of dilute aqueous solutions containing ethoxylated nonionic surfactants is increased, the solutions may turn cloudy at a certain temperature, called the cloud point. At or above the cloud point, the cloudy solution may separate into two isotropic phases, one concentrated in surfactant (coacervate phase) and the other containing a low concentration of surfactant (dilute phase). As an example of the importance of this phenomena, detergency is sometimes optimum just below the cloud point, but a reduction in the washing effect can occur above the cloud point (95). However, the phase separation can improve acidizing operations in oil reservoirs (96) For surfactant mixtures, of particular interest is the effect of mixture composition on the cloud point and the distribution of components between the two phases above the cloud point. 

From Figures 3 and 6—9, the predicted total adsorptions For surFactant mixtures are higher than observed values. ThereFore, the mixed admicelles showed positive deviation From ideality at all compositions. This remarkable behavior has not been observed beFore because data oF the accuracy and range reported here has not (to our knowledge) previously been reported. Observation oF the expected ideal behavior For the CMC data indicate that this is probably not due to a peculiarity oF the surFactants used. 

Methods. The adsorption was determined by adding a surfactant mixture of known composition to the emulsifier-free latex. The solid/solution ratio was held constant at 0.17 w/w. In this way a series of adsorption measurements was performed with increasing total surfactant concentration. Note that, while the ratio of the two surfactants in such a series is constant in the whole system, it is not necessarily constant on the surface or in the solution because of the preferential adsorption of one of the surfactants. 

The composition of the surfactant mixture in the equilibrium solution is described by the quantity... 

Thus, a rough estimate of the surface composition, at solution concentrations around the cmc of the surfactant mixture, should be possible provided that the cmc s of the single surfactants are known. 

J.S. D Arrigo, C. Saiz-Jimenez and N.S. Reimer, Geochemical properties and biochemical composition of the surfactant mixture surrounding natural microbubbles in aqueous media, J. Colloid Interface Sci. 100 (1984) 96-105. 

Table IV. Monoalkyl/dialkyl cationic surfactant mixtures sample composition...

An amine oxide surfactant solution can be modeled as a binary mixture of cationic and nonionic surfactants, the composition of which is varied by adjusting the pH. The cationic and nonionic moieties form thermodynamically nonideal mixed micelles, and a model has been developed which quantitatively describes the variation of monomer and micelle compositions and concentrations with pH and... 

With the objective of designing new compositions of synthetic substitutes for the native lung surfactant, it is desirable to control the physical state and properties of dipalmitoylphosphatidylcholine (DPPC) spread at the air/water interface. DPPC is the main component of the native lung surfactant, which also comprises a complex mixture of lipids and specific proteins [62], Langmuir monolayers provide a model of the air/alveolar interface that is widely used for assessing the properties of lung surfactant replacement compositions. 

The extraction performances under different experimental conditions (i.e. varying the pH, the composition of surfactant mixtures, the amount of chelating compound) were also investigated for our test system. The results are shown in Table III. 

Emulsion Solvent Evaporation The basic concept of the emulsion solvent evaporation technique producing nanoparticles is very straightforward. The particles are formed as an emulsion of a polymer-surfactant mixture and dispersed in an organic solvent. The solvent is then evaporated to leave behind the individual emulsion droplets which form stable free nanoparticles [203], This method is far easier and more preferable over methods such as spray drying and homogenization and operates under ambient conditions and mild emulsification conditions. The size and composition of the final particles are affected by variables such as phase ratio of the emulsion system, organic solvent composition, emulsion concentration, apparatus used, and properties of the polymer [204],... 

One of the medical problems already raised in sec. I.l, is that premature babies may not have produced enough of the surfactant mixtures, leading to so-called respiratory distress syndrome (RDS), This disease is nowadays readily overcome by letting the baby inhale a spray containing the mixture. The remedy is facilitated by the non-specificity of the mixture the composition is not as critical as it would have been in say, implants. 

The molecular shape is not the sole determinant of the structure of the aggregate. If the suifactant-water mixture is to form a single phase, the smface and volume requirements set by the composition of Ae mixture must be satisfied. Introducing the global constraint set by the composition leads to an estimate of the relation between the local geometry (expressed by the surfactant parameter) and the composition at which the surfactant mixture is expected to form a bilayer - or reversed bilayer - wrapped onto an IPMS (illustrated in Fig. 4.7). 

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