Polyoxyethylene surfactants, cloud point

Increasing polyoxyethylene chain length (Figure 11 A-C) increases the PIT, similar to an increase in surfactant cloud point. The general trend expected (such as increasing water solubility) is also observed in... 

The effect characteristic of a multi-chain hydrophobe, that is, increase in the cmc and simultaneous decrease in the cloud point, appears to be inconsistent with the well-known HLB concept in surfactants. Tanford has pointed out that based on geometric considerations of micellar shape and size, amphiphilic molecules having a double-chain hydrophobe tend to form a bilayer micelle more highly packed rather than those of single-chain types ( ). In fact, a higher homologue of a,a -dialkylglyceryl polyoxyethylene monoether has been found to form a stable vesicle or lamellar micelle (9 ). Probably, the multi-chain type nonionics listed in... 

Cloud point extraction of metal ions. The use of cloud point extraction as a separation technique was first introduced by Watanabe for the extraction of metal ions forming sparingly water soluble complexes [109], Since then, the technique has been applied successfully to the extraction of metal chelates for spectrophotometric, atomic absorption, or flow injection analysis of trace metals in a variety of samples [105-107,110]. Other metal complexes such as AUCI4 or thiocyanato-metal complexes can be extracted directly using nonionic surfactants such as polyoxyethylene... 

Caution should be exercised when considering temperature effects on solubilization by micelles, since the aqueous solubility of the solute and thus its micelle/water partition coefLcient can also change in response to temperature changes. For example, it has been reported that although tt solubility of benzoic acid in a series of polyoxyethylene nonionic surfactants increases with temperature, the micelle/water partition coefLci rt, shows a minimum at 2C, presumably due to the increase in the aqueous solubility of benzoic acid (Humphreys and Rhodes, 1968). The increasr in Km with increasing temperature was attributed to an increase in micellar size, as the cloud point temperature of the surfactant is approached (Humphreys and Rhodes, 1968). 

A plot of the temperatures required for clouding versus surfactant concentration typically exhibits a minimum in the case of nonionic surfactants (or a maximum in the case of zwitterionics) in its coexistence curve, with the temperature and surfactant concentration at which the minimum (or maximum) occurs being referred to as the critical temperature and concentration, respectively. This type of behavior is also exhibited by other nonionic surfactants, that is, nonionic polymers, // - a I k y I s u I Any lalcoh o I s, hydroxymethyl or ethyl celluloses, dimethylalkylphosphine oxides, or, most commonly, alkyl (or aryl) polyoxyethylene ethers. Likewise, certain zwitterionic surfactant solutions can also exhibit critical behavior in which an upper rather than a lower consolute boundary is present. Previously, metal ions (in the form of metal chelate complexes) were extracted and enriched from aqueous media using such a cloud point extraction approach with nonionic surfactants. Extraction efficiencies in excess of 98% for such metal ion extraction techniques were achieved with enrichment factors in the range of 45-200. In addition to metal ion enrichments, this type of micellar cloud point extraction approach has been reported to be useful for the separation of hydrophobic from hydrophilic proteins, both originally present in an aqueous solution, and also for the preconcentration of the former type of proteins. 

The wetting of a liquid drop placed on a solid surface has already been described (Section 3.4) by the critical surface tension of the surface and by Young s equation. Temperature is a factor in wetting by aqueous solutions since it influences surfactant solubility. For example, the fastest wetting for polyoxyethylenated non-ionic surfactants is produced by those whose cloud points are just above the use temperature [193]. 

Mitchell, D.J., Tiddy, G.J.T., Warring, L., Bostock, T. and Me Donald, M.P. (1983) Phase behavior of polyoxyethylene surfactants with water, mesophase structures and partial miscibility (cloud points). /. Chem. Soc. Faraday Trans. I, 79(4), 975-1000. 

We have examined the stmcture of both ionic and nonionic micelles and some of the factors that affect their size and critical micelle concentration. An increase in hydrophobic chain length causes a decrease in the cmc and increase of size of ionic and nonionic micelles an increase of polyoxyethylene chain length has the opposite effect on these properties in nonionic micelles. About 70-80% of the counterions of an ionic surfactant are bound to the micelle and the nature of the counterion can influence the properties of these micelles. Electrolyte addition to micellar solutions of ionic surfactants reduces the cmc and increases the micellar size, sometimes causing a change of shape from spherical to ellipsoidal. Solutions of some nonionic surfactants become cloudy on heating and separate reversibly into two phases at the cloud point. 

DJ. Mitchell, GJ.T. Tiddy, L. Waring, T. Bostock, and M.P. McDonald, Phase-Behavior of Polyoxyethylene Surfactants with Water - Mesophase Structures and Partial Miscibiliity (Cloud Points). J. Chem. Soc., Faraday Trans. 1, 1983, 79, 975-1000. 

A combination of SLS and DLS methods was used to investigate the behavior of nonionic micellar solutions in the vicinity of their cloud point. It had been known for many years that at a high temperature the micellar solutions of polyoxyethylene-alkyl ether surfactants (QEOm) separate into two isotropic phases. The solutions become opalescent with the approach of the cloud point, and several different explanations of this phenomenon were proposed. Corti and Degiorgio measured the temperature dependence of D pp and (Ig), and found that they can be described as a result of critical phase separation, connected with intermicellar attraction and long-range fluctuations in the local micellar concentration. Far from the cloud point, the micelles of nonionic surfactants with a large number of ethoxy-groups (m 30) may behave as hard spheres. ... 

Polyethylene glycol 200 decyl ether Polyoxyethylated (6) isodecyl alcohol Polyoxyethylene (4) decyl ether Polyoxyethylene monodecyl ether Prox-onic DA-1/04 Rhodasurl DA-4 3,6,9,12-Tetraoxadocosan-1-ol Trycol 5950 Surfonic DA-6 Synthrapol KB PEG-6 decyl ether. Wetting agent for built scour systems. Detergent penetrant emulsifier for textiles, clay soils, fire fighting surfactant. Oil d = 1.0014 viscosity = 109 cps HLB 12.5 hyd no 132 pour point =12.8" cloud point = 42". Rhdne Poulenc Surfactants,... 

Non-ionic surfactants do not exhibit Krafft points. Rather the solubility of non-ionic 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, polyoxyethylenated non-ionics decreases sharply above their cloud points. The addition of electrolyte usually lowers the cloud point while the addition of ionic surfactant usually increases the cloud points of their non-ionic counterparts, this increase being dependent on the composition of the mixed micelle. 

The clouding temperature or the cloud point depends strongly on the polyoxyethylene chain length but is less influenced by the hydrophobe size. Normally, the cloud point is recorded for a certain fixed solute concentration (say 1 wt%). The cloud point of C12E8 is around 80°C, while it is ca. 50 and lO C for C12E6 and C12E4, respectively. For still shorter polyoxyethylene chains, the surfactant is insoluble even at the freezing temperature of water, so the cloud point is below 0°C. 

It is generally found that the same circumstances that affect the solution characteristics of nonionic surfactants (their cmc, micelle size, cloud point, etc.) will also affect the PIT of emulsions prepared with the same materials. For typical polyoxyethylene nonionic surfactants, increasing the length of the POE chain will result in a higher PIT for a given oil-aqueous phase combination (Fig. 11.12), as will a broadening of the POE chain length distribution. The use of phase inversion temperatures, therefore, represents a very useful... 

If the solubility of a surfactant is highly temperature-dependent, as is the case for many nonionic polyoxyethylene surfactants and long chain fatty acid soaps such as sodium stearate, it will be found that foaming ability will increase in the same direction as its solubility. Nonionic POE surfactants, for example, exhibit a decrease in foam production as the temperature is increased and the cloud point is approached (solubility decreases). Long-chain carboxylate salts, on the other hand, which may have limited solubility and poor foaming properties in water at room temperature, will be more soluble and will foam more as the temperature increases. 

The temperature dependence of the cmc of polyoxyethylene nonionic surfactants is especially important since the head group interaction is essentially totally hydrogen bonding in nature. Materials relying solely on hydrogen bonding for solubilization in aqueous solution are commonly found to exhibit an inverse temperature-solubility relationship. As already mentioned, major manifestation of such a relationship is the presence of the cloud point for many nonionic surfactants. 

Non-ionic Surfactants. These surfactants do not present the Krafft phenomenon. However, a nonionic micellar solution becomes turbid and separates in two phases when the temperature is raised. This is the clouding phenomenon. The polyoxyethylene chain, the polar part of most non-ionic surfactants, is progressively dehydrated as the temperature raises. Losing water molecules, the polyoxyethylene ehain becomes less polar and, at a particular temperature, a turbidity, the clouding, appears. This temperature is called the cloudpoint of the nonionic surfactant solution. Above the cloud point, the nonionic micellar solution separates in an aqueous phase saturated by the nonionic surfactant, and an organic phase saturated by water and containing the major part of the surfactant. 

The cloud point temperature depends on the concentration of surfactant. It increases significantly with the polyoxyethylene chain length, but scarcely depends on the polar chain length. As an example, the cloud points of some nonionic Pluronic surfactants (see Table 2.3) are listed in Table 2.8. The nonionic micelle size and aggregation number increases dramatically with temperature. It can be stated that the aggregation number becomes infinite at the clouding temperature. 

Micellar-mediated preconcentration is a form of cloud point extraction, which involves the use of polyoxyethylene-10-lauryl ether as a surfactant for PAH extraction. The water sample from which PAHs are to be extracted is mixed with an adequate polyox)dhylene-10-lauryl ether concentration to obtain a final solution of 1% (w/v) in the surfactant. Then the aliquot is kept in a thermostatically controlled bath. After about 90 min the supernatant surfactant-rich phase is withdrawn using a microsyringe [47]. 

---