Phase of nonionic surfactants

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

Guha, S. and Jaffe, P. R. (1996). Biodegradation kinetics of phenanthrene partitioned into the micellar phase of nonionic surfactants, Environ. Sci. Technol., 30, 605 611. 

Olsson, U. and Wennerstrom, H., Globular and bicontin-uous phases of nonionic surfactant films, Adv. Colloid Interface ScL, 49, 113-146 (1994). 

Microelectrodes with high real surface areas and well-defined periodic nanostmctures have recently attracted much interest because of their potential applications in electrocatalysis and electroanalysis [94-96]. These electrode systems can be prepared, using templating techniques, from lyotropic liquid crystalline phases of nonionic surfactants [94,95]. In particular, the normal topology hexagonal (Hj) liquid crystalline phase has been used as a template for the synthesis of mesoporous metal thin films via the electrochemical reduction of metal salts dissolved in the aqueous domain of the liquid crystalline phases [119, 120]. 

For details of the spatial organization within the mesomorphic phases of nonionic surfactants, the reader is referred to reviews by Corkill and co-workers [9,10] and Winsor [11]. 

Fig. XIV-10. The correlation between the HLB number and the phase inversion temperature in cyclohexane of nonionic surfactants. (From Ref. 71.)...

Many solutions of common nonionic surfactants and water separate into two phases when heated above a certain temperature (the cloud point), and some investigators call the phase of greater surfactant concentration, a microemulsion. Thus, there is not even universal agreement that a microemulsion must contain oil. 

Eigure 6 illustrates how the three tensions among the top, middle, and bottom phases depend on temperature for a system of nonionic surfactant—oil—water (38), or on salinity for a representative system of anionic surfactant—cosurfactant—oil—water and electrolyte (39). As T approaches from lower temperatures, the composition of M approaches the composition of T, and the iaterfacial teasioa betweea them, goes to 2ero at T =. ... 

An alternate approach for biomolecule recover is to employ degradable surfactants [157]. A series of nonionic surfactants has been synthesized that contain the acidic pH-degradable cyclic ketal linkage [153]. These surfactants readily form w/o-MEs when at neutral pH or higher but, the surfactants readily degrade at moderately low pH (ca. 5), releasing the encapsulated aqueous phase and its constituents. Work is ongoing to develop these surfactants in w/o-ME protein extraction processes [153]. 

M. Tang and S.N. Deming, Interfacial tension effects of nonionic surfactants in reversed-phase liquid chromatography , Anal. Chem., 1983, 55, 425. 

Penetration of the surfactant demands a certain minimum lipophilicity. Partitioning of nonionic surfactants into simple organic phases has been measured for a limited range of nonionics. Crook et a. Cl ) and Harusawa (i5, 16)... 

The most frequent emulsiflcation using phase inversion is known as the PIT (Phase Inversion Temperature) method [81-83] and occurs through a temperature quench. This method is based on the phase behavior of nonionic surfactants and the correlation existing between the so-called surfactant spontaneous curvature and the type of emulsion obtained. 

Lamellar phases of phosphohpids and other HpophiHc surfactants can be dissolved, i.e., converted into micellar solutions, by contacting them with aqueous phases of hydrophihc surfactants, a phenomenon that is sometimes desirable and sometimes undesirable in studies of biological membranes. Often myehnic figures form during the dissolution process. Simoes et al. [33] reported rates of dissolution of various mixtures of phosphatidylchohne and the nonionic surfactant Tween 80. 

Bourrel M, Salager JL, Schechter RS, Wade WH (1980) A Correlation for Phase Behavior of Nonionic Surfactants. J Colloid Interface Sci 75 451-461... 

In order to define a ionic/nonionic surfactant solution with high salinity/hardness tolerance, the following criterion should be followed. The mixed micelle should have as large of a negative deviation from ideality as possible. Surfactant mixture characteristics which result in this have already been discussed. The nonionic surfactant should have a high cloud point. Otherwise the amount of nonionic surfactant which can be added to the system is limited to low levels before phase separation occurs. If possible, a mixed ionic surfactant should be used for reasons Just discussed. There is no such benefit to using mixed nonionic surfactants, although this is not necessarily detrimental either. 

The cloud point of a mixture of nonionic surfactants is intermediate between the pure nonionic surfactants involved (95.99) The cloud point of a dilute nonionic surfactant solution increases upon addition of ionic surfactant (95.98—104). The coacervate phase forms because of attractive forces between the micelles in solution. The incorporation of ionic surfactant into the nonionic micelles introduces electrostatic repulsion between micelles, causing coacervate phase formation to be hindered, raising the cloud point. 

A considerable amount of experimental work has been carried out on the so-called gel emulsions of water/nonionic surfactant/oil systems [9-14, 80, 106, 107]. These form in either the water-rich or oil-rich regions of the ternary phase diagrams, depending on the surfactant and system temperature. The latter parameter is important as a result of the property of nonionic surfactants known as the HLB temperature, or phase inversion temperature (PIT). Below the PIT, nonionic surfactants are water-soluble (hydrophilic form o/w emulsions) whereas above the PIT they are oil-soluble (hydrophobic form w/o emulsions). The systems studied were all of very high phase volume fraction, and were stabilised by nonionic polyether surfactants. 

Finally, some studies have been performed on the addition of salt to the aqueous phase of oil-in-water HIPEs [109]. For systems stabilised by ionic surfactants, increasing salt concentration reduces the double-layer repulsion between droplets however, stability is more or less maintained, probably due to steric and polarisation repulsions. Above a sufficiently high salt concentration, emulsions become unstable due to salting-out of the surfactant into the oil-phase. For nonionic surfactants, the situation is similar, except that there are no initial double-layer forces. In addition, Babak [115] found that increasing the electrolyte concentration reduced the barrier to coagulation between emulsion droplets, and therefore increased coalescence. Generally, therefore, stability of o/w HIPEs is not enhanced by salt addition. 

The preliminary results reported here indicate that the general changes induced in the PIT range may help to systematize the complex phase behavior of nonionic surfactants when they are combined with water and hydrocarbons. 

K. Shinoda and H. Takeda, The effect of added salts in water on the hydrophile-lipophile balance of nonionic surfactants the effect of added salts on the phase inversion temperature of emulsions, J. Colloid Interface Sci. 32 (1970) 642-646. 

Early oxidation hair dyes were used in solution form these have been replaced by cream- or gel-based formulas. The oil-in-water emulsions commonly used can be supplemented with auxiliary ingredients, such as polymers to improve combing ability, as well as other conditioning additives. Extensive patent literature is available on this point [35], Gel formulations may be based on alcoholic solutions of nonionic surfactants or fatty acid alkanolamide solutions, which form a gel when mixed with the oxidant. The type (emulsion or gel) and the basic composition of the preparation strongly influence dyeing [47], Different base formulations with the same dye content yield varying color depths and shading due to the distribution of the dye between the different phases of the product, interaction with surfactants, and diffusion from the product into the hair. 

Non-ionic surfactants do not exhibit Krafft points. Rather the solubility of nonionic surfactants decreases with increasing temperature and the surfactants begin to lose their surface active properties above a transition temperature referred to as the cloud point. This occurs because above the cloud point a separate surfactant-rich phase of swollen micelles separates the transition is visible as a marked increase in dispersion turbidity. As a result, the foaming ability of, for example, polyoxyethyle-nated non-ionics, decreases sharply above their cloud points. The addition of electro-... 

Quinones-Torrelo et al. (1999 2001) have demonstrated a correlation of pharmacokinetic properties with results from micellar liquid chromatography. In this method micellar solutions of nonionic surfactants are used as the mobile phase in reverse-phase liquid chromatography. Interactions between the mobile and stationary phases are purported to correspond to the membrane/water interface of biological barriers as hydrophobic, steric, and electronic interactions are important for both. For a series of 18 antihistamines Quinones-Torrelo et al. (2001) showed that both volume of distribution and half-life values were better correlated with retention on these columns than with the classical log K, w descriptor. 

For a constant amount of nonionic surfactant, the interfacial tension at the planar oil-water interface, for the same amounts of oil and water, passes through a minimum when plotted against the hydrophilic-lipophilic balance (HLB). The emulsion stability passes through maxima in the W/O and O/W ranges and through a minimum between the two at the phase inversion point. The minima in the two cases coincide. These observations are explained on the basis of thermodynamics. The stability of macroemulsions can be correlated with the surface excess of surfactant, which also passes through two maxima and a minimum between them [2.11]. 

Based upon the use of nonionic surfactant systems and their cloud point phase separation behavior, several simple, practical, and efficient extraction methods have been proposed for the separation, concentration, and/or purification of a variety of substances including metal ions, proteins, and organic substances (429-441. 443.444). The use of nonionic micelles in this regard was first described and pioneered by Watanabe and co-workers who applied the approach to the separation and enrichment of metal ions (as metal chelates) (429-435). That is, metal ions in solution were converted to sparingly water soluble metal chelates which were then solubilized by addition of nonionic surfactant micelles subsequent to separation by the cloud point technique. Table XVII summarizes data available in the literature demonstrating the potential of the method for the separation of metal ions. As can be seen, factors of up to forty have been reported for the concentration effect of the separated metals. 

TABLE XVII. Summary of the Reported Extraction of Metal Ions as Metal Chelates by the Phase Separation Behavior of Nonionic Surfactants... 

A series of 4-alkylamido-2-hydroxybenzoic acids containing a different number of carbon atoms in the alkyl-amido group has been studied as model ligands for metal ion extraction in aqueous micellar solutions of nonionic surfactants. Their acid-base properties and reactivity towards metal ions in the presence of micelles were investigated. By operating at a proper temperature, the separation of the iron (III) chelate complexes into a micellar rich phase was achieved and the extraction efficiency was correlated with the ligand hydrophobicity. 

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