Krafft point definition

As can be seen, concepts of the Krafft point fall ito two different categories those involving a phase transition of solid surfactant and those involving a solubility increase up to the CMC. The two views are incompatible according to the former, the Krafft point is a definite temperature (a point), whereas according to the latter, it is a narrow temperature range. This conflict is addressed in the following sections. 

It can be concluded that the Krafft point is the temperature at which the solubility of surfactants as monomers becomes high enough for the monomers to commence aggregation or micellization. Recall from Chapter 4 that the CMC depends on the method used for its determination, and that the CMC value should therefore be defined as a narrow temperature range even though the solubility is definitely determined by temperature... 

The definition of the MTR adopted above can be used to explain several experimental facts. The Krafft points of homologous ionic surfactants have been reported to increase with increasing alkyl chain length. 

The choice of 20 mN m" as a standard value of surface tension lowering for the definition of adsorption efficiency is convenient, but, as mentioned, somewhat arbitrary. When one discusses the effectiveness of adsorption, as defined as the maximum lowering of surface tension regardless of surfactant concentration, the value of o-min is determined only by the system itself and represents a more firmly fixed point of reference. The value of oinm for a given surfactant will be determined by one of two factors (1) the solubility limit or Krafft temperature (Tk) of the compound, or (2) the critical micelle concentration (cmc). In either case, the maximum amount of surfactant adsorbed is reached, for all practical purposes, at the maximum bulk concentration of free surfactant. 

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