Cloud point of ethoxylates

Figure 31. Cloud point of ethoxylates at reduced concentrations...

The electrolyte effect of some water-soluble monomers on the cloud point of ethoxylated surfactants is illustrated in Figure 4. In the absence of salt, the cloud point of the emulsifier blend (6 1086 Arlacel 83, HLB = 9.3) is equal to 64°7 ( ). Three monomers-sodium acrylate, MADQUAT - ADQUAT (acryloxyethyltrimethylammonium chloride) - salt the surfactant blend out, the strongest effect being observed with ADQUAT ( 9). 

The origins of the cloud point of ethoxylate nonionics are not yet fully imderstood we can, however, mention the most reliable explanations behind this behavior. The general explanation of the decrease in solubility at higher temperatures is an increase in the effective attraction between solute like molecules and surfactant dehydration. These rationales derived from thermodynamic or conformational considerations can account for this behavior ... 

Interestingly, the effectiveness of salts in lowering the consolute temperature of polyoxyethylene in water exactly parallels the effectiveness of salts in lowering the cloud point of ethoxylated nonionic surfactants (16,... 

A significant increase in fp and similar elongated drops and emulsification were seen as the cloud point of 37 °C was approached for Dow s commercial secondary alcohol ethoxylate Tergitol 15-S-7 (Fig. 5). Its hydrophobe consists of various double-chain species with the sum of the chain lengths ranging between 11 and 15, and its average EO number is 7.3. In some cases a conical projection developed on the elongated drop, and a jet was emitted, which broke up into small droplets (Eig. 6). 

Genapol 26-L-60 C12C16 alcohol ethoxylate with cloud point of 60C Hoechs... 

Table 5.2 Typical cloud points of nonylphenol ethoxylates...

TTAB, in combination with an alkyl ethoxylated sulfate, also lowers the surface tension observed at CMC by approximately 10 dyne cm-1 compared to either of the surfactants alone. It is postulated that the combination of the anionic and cationic results in charge neutralization providing a net surfactant which is similar to a nonionic surfactant. This is confirmed by the lowering of the cloud point of the surfactant combination as the mole fraction of anionic and cationic are adjusted to near the equivalency point. 

The nonlonlc microemulsion used is a well characterized aizjA) nonionic mlcroemulslon with Brij-96 (oleyl-10 ethoxylate) as the primary surfactant, n-butanol as the cosurfactant and hexadecane in the weight ratio of 5.32/2.78/0.90. When diluted with water to 9Z, oil + surfactant + cosurfactant, this forms a water clear mlcroemulslon having a sharp cloud point of about 58 C. The cloud point of this mlcroemulslon is depressed to about 51 C when the external phase is 2 wt X NaCl in water. 

Dimethicone copolyols exhibit an inverse cloud point phenomenon as an aqueous solution is heated. This same phenomenon is observed with ethoxylated fatty alcohol. The hydrogen bonding of the water with the polyoxyethylene portion of the molecule causes the cloud point. The inverse cloud point of the molecule is related to the length of the ethylene oxide chain and not the number of D units or molecular weight. The term inverse cloud point refers to the temperature at which a clear solution develops turbidity on heating. Cloud point is a phenomenon, relating to tnrbidity, which develops on cooling. 

Various other procedures have been developed to obtain a rough estimate of the HLB number. GrifEn found a good correlation between the cloud point of a 5% solution of various ethoxylated surfactants and their HLB number (see Figure 6.20). 

At low temperatures, the ethoxylated surfactant is soluble in water and at a given concentration is can solubilise a given amount of oil. The oil solubilisation increases rapidly with rising temperature near the cloud point of the surfactant -this is illustrated in Figure 10.6, which shows the solubilisation and cloud point curves of the surfactant. Between these two curves, an isotropic region of O/W solubilised system exists. 

Ci2 16 methyl ester ethoxylate requires about two additional moles of ethylene oxide compared to a C12 16 linear alcohol ethoxylate. To obtain an inverse cloud point of 80 °C, approximately eight additional moles of ethylene oxide would be needed. 

Ethoxylated nonionic surfactants are less soluble in water at higher temperatures. Thus, at high concentrations, some may be isolated simply by heating an aqueous solution above the cloud point of the surfactant, which forms a separate layer and can be removed. The process must be repeated several times for reasonable recovery. The separated phase will be enriched in the more hydrophobic homologs compared to the original surfactant. This phase may also act as an extraction medium to concentrate other components of the solution. 

Hydrophobic ultrafiltration membranes allow the above phenomenon to be used in reverse, permitting surfactant to permeate the membrane but holding back soil and oil (102,103). In this case, the surfactant concentration is enriched in the permeate, presumably because adsorption of the surfactant (alcohol ethoxylates) to the membrane aids in permeation. It is important to control the temperature below the cloud point of the surfactant (103). 

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. 

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 ... 

The physical chemical properties of the surfactants that contain an ester bond between the hydrophobic tail and the polar head group are very similar to those of alcohol ethoxylates of the same alkyl chain length and the same number of oxyethylene units. The CMC and the cloud point values of the linear ester surfactant 1 of Fig. 4 are approximately the same as those of the straight chained alcohol ethoxylate tetra(ethylene glycol)monooctyl ether (C8E4), i.e., around 10 mM and 40 °C, respectively. Thus it appears that the... 

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. 

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