Nonionic cloud point

Future work in this area should focus on further development of novel extraction schemes that exploit one or more of the cited advantages of the nonionic cloud point method. It is worth noting that certain ionic, zwitterionic, microemulsion, and polymeric solutions also have critical consolution points (425,441). There appear to be no examples of the utilization of such media in extractions to date. Consequently, the use of some of these other systems could lead to additional useful concentration methods especially in view of the fact that electrostatic interactions with analyte molecules is possible in such media whereas they are not in the nonionic surfactant systems. The use of the cloud point event should also be useful in that it allows for enhanced thermal lensing methods of detection. 

MONA NF products display the solubility characteristics of ionic surfactants in alkaline builder concentrates but, when diluted, they exhibit nonionic cloud point bahaviot. They ofer the following advantages ... 

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. 

In most cases, these active defoaming components are insoluble in the defoamer formulation as weU as in the foaming media, but there are cases which function by the inverted cloud-point mechanism (3). These products are soluble at low temperature and precipitate when the temperature is raised. When precipitated, these defoamer—surfactants function as defoamers when dissolved, they may act as foam stabilizers. Examples of this type are the block polymers of poly(ethylene oxide) and poly(propylene oxide) and other low HLB (hydrophilic—lipophilic balance) 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. 

Cloud Points The influence of added NaCl on the observed cloud points of 1% W/V solutions of the four nonionic surfactants under observation are given in Figure 1. Approximately linear correlations were observed as the aqueous NaCl level was increased, with negative coefficients recorded between 0.22 - 0.3 K.g "1dm3. Higher loadings of surfactant were found to increase the cloud point. It was observed also that the inclusion of small quantities of oils to surfactant solutions could either elevate or depress the cloud point. The significance of this fact will be developed later. 

When scouring synthetic fibres that are to be dyed with disperse dyes, nonionic scouring agents are best avoided unless they are formulated to have a high cloud point and are known not to adversely affect the dispersion properties of the dyes. Conversely, when scouring acrylic fibres, anionic surfactants should be avoided [156] because they are liable to interfere with the subsequent application of basic dyes. These fibres are usually scoured with an ethoxylated alcohol, either alone or with a mild alkali such as sodium carbonate or a phosphate. 

Surprisingly, other investigators were unable to confirm the adverse effect of nonionic surfactants of low cloud point in the high-temperature dyeing of polyester, even in the presence of electrolytes [111]. This was probably because of the rather low concentrations used. Adducts containing a C18-C2o hydrophobe and a decaoxyethylene hydrophile, as well... 

The adverse effect of nonionic adducts of low cloud point can be avoided by the use of hybrid agents of the ethoxylated anionic type, variously and confusingly referred to as modified nonionic , modified anionic or weakly anionic types. Thus Mortimer [113] has proposed the use of products of the ethoxylated phosphate type (12.27). In this structure, R, as well as the degree of ethoxylation (n) may be varied to optimise the overall HLB value. The numerous ether groups are said to enhance the dye-solubilising and levelling capacity, whilst the polyphosphate grouping exerts several useful effects [113]. These compounds ... 

Performance Indices Quality Factors Optimum E1LB Critical micelle concentration (CMC) Soil solubilization capacity Krafft point (ionic surfactants only) Cloud point (nonionic surfactants only) Viscosity Calcium binding capacity Surface tension reduction at CMC Dissolution time Material and/or structural attributes... 

Krafft point (for ionic surfactants) and cloud point (for nonionic surfactants) are both a limit to surfactant solubility. The solubility of ionic surfactants decreases significantly below the Krafft point, since its concentration falls below the CMC and individual surfactant molecules cannot form micelles. Therefore, the Krafft point of an ionic surfactant must be below the desired wash temperature for maximum soil removal. In contrast, the solubility of some nonionic surfactants decreases with increasing temperature. Above the cloud point, the surfactant becomes insoluble. Thus, the cloud point of a nonionic surfactant should be 15-30°C above the intended wash temperature [8],... 

Table IV shows a comparison of some aqueous solution properties of nonionics having the same total number (ten) of carbon atoms in the hydrophobe and a comparable POE chain length, but different hydrophobe structure. It can be seen that multi-chain hydrophobes bring about a striking decrease in the cloud point and in the surface tension at the cmc, and an increase in the cmc, while cyclic fixation of the alkyl chain causes a large increase in the cloud point, the cmc and in the surface tension at the cmc.

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... 

Thus, an estimation can be made of the hydrophilicity of the crown ring. The acetal-type crown ring obtained from hexaethyl-ene glycol and a higher aliphatic aldehyde is estimated to be e-quivalent to about four OE units in an alkyl POE monoether, from our study of the cloud point (11). Moroi et al. concluded, from a comparison of the cmc, that a diaza-18-crown-6 is equivalent to 20 OE units in the usual type of nonionic (12). Okahara s group evaluated the effective HLB based on the cloud point, phenol index and phase-inversion-temperature in emulsion of oil/water system and they concluded that 18-crown-6 and monoaza-18-crown-6 rings with dodecyl group are approximately equivalent to 4.0 and 4.5 units, respectively, of OE chains with the same alkyl chain (17). 

Surface-active crown ethers are distinctly differ from usual type of nonionics in salt effect on the aqueous properties, due to the selective complexing ability with cations depending on the ring size of the crown. As shown in Figure 3 (22), the cloud point of the crowns is selectively raised by the added salts. This indicates that the degree of cloud point increase is a measure of the crown-complex stability in water (23). 

Table VII. Melting Point, Krafft Nonionics Point and Cloud Point of...

Figure 6. Plots of cloud point vs. number of carbon atoms in the acyl or alkyl group for nonionics Cj GE C—O—), Cj AE C ...

Figure 9 shows the effect of acyl chain length (N) on the binary phase diagram of G type nonionics. The area of neat phase spreads with increasing N and the extension of the area takes rapid strides between N of 12 and 14. This N is just in accord with that of the sharp minimum in the cloud point - N curve of the G type. The same thing has also been found for the relation between the effect of OE number on the area of the neat phase and the minimum in the cloud point - OE number curve of CiaGE j (m = 2 - 4). 

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