Surfactants Kraft point

The Kraft point (T ) is the temperature at which the erne of a surfactant equals the solubility. This is an important point in a temperature-solubility phase diagram. Below the surfactant cannot fonn micelles. Above the solubility increases with increasing temperature due to micelle fonnation. has been shown to follow linear empirical relationships for ionic and nonionic surfactants. One found [25] to apply for various ionic surfactants is ... 

Stroink [61] and Meijer [64] describe the hard water stability of several ether carboxylates with different fatty chains and EO degrees compared to some basic surfactants (Tables 2 and 3). Studies with carboxymethylated alcohols [52] based on C12 to C18 compared to the corresponding fatty acids showed an important solubility in hard water, although the CMC was still close to those of these fatty acids. With increasing water hardness the Kraft points of the carboxymethylated products increased. 

The surfactant counterion is important in MECC because it affects the Kraft point, that is, the temperature above which the solubility of the surfactant increases sharply as a result of micelle formation SDS has a lower Kraft point than potassium dodecyl sulfate and will therefore reach its CMC at a lower temperature. In MECC, many separation problems can be solved with standard MECC buffers and operating conditions Table 5.4 provides a list of standard operating conditions.19... 

The addition of an ethylene oxide chain to what is essentially an alkyl sulphate changes its properties in several important ways. Firstly the Kraft point is very significantly reduced. Low active solutions of ether sulphates are clear are fluid at temperatures close to 0°C, and the Kraft point reduces with increasing levels of ethoxylation. Secondly, the nature of foam changes, from the dense stable foam of an alkyl sulphate to a much more open foam structure. The tolerance of the surfactant to water hardness is also improved, with ether sulphates showing better foaming in the presence of moderate hardness. 

Applications. Sarcosinates show low irritation potential and are good foamers. Due to these properties they find applications in personal care products where synergistic effects with other surfactants may also be exploited. In combination with other anionics, sarcosinates will often detoxify the formulation and give improved foaming and skin feel. Sarcosinates are also used for their hydrotropic properties - the addition of sarcosinate to other anionics often gives a reduced Kraft point or a raised cloud point if combined with non-ionic surfactants. Lauroyl sarcosinate is used to formulate SLS-free toothpastes which are claimed to have improved taste profile. 

Gu T and SJoblom J 1991 Empirical relationships between the Kraft points and the structural units in surfactants Acta Chem. Scand. 45 762-5... 

For the case of ionic surfactants, the attainment of the CMC is not the only necessary condition to form micelles the Kraft point T of the surfactant has also to be taken into account. If the temperature is below T, a given surfactant is not soluble enough to reach the CMC and thus micelles are not formed. values for several surfactants are reported in Reference 25 and in manufacturers technical sheets. 

Similarly, the surfactant insoluble in water would go well for the water-in-oil emulsions. The nonionics generally separate out from water at higher temperatures, mainly due to the dehydration of the water-soluble surfactants. At the temperature at which the dehydration of surfactant occurs, the solution turns turbid, and the temperature is considered as the cloud point of the surfactant. The cloud point is lowered in the presence of electrolytes. Based on the effect of temperature and electrolytes on the cloud point of nonionic surfactants, one can select the suitable surfactant contrary to this, the solubility of anionic surfactant increases with increase in temperature. The temperature at which solubility shows a sharp rise is called the Kraft point of anionic surfactants. 

Figure 13.3 shows a simplified phase diagram of an aqueous surfactant system. The Kraft point is the temperature at which the surfactant solubility is equal to the critical micelle concentration (CMC). When the temperature is lower than the Kraft temperature, the surfactant exists in gel or crystal form in the solution. When the temperature is above the Kraft temperature and the surfactant concentration is higher than the CMC, the micelles are formed in the surfactant solution. The micelles are initially spherical in shape. With the increase in surfactant concentration or upon... 

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