Incolloidal chemistry, theKrafft temperature (orKrafft point, after German chemistFriedrich Krafft) is defined as the minimumtemperature at which the formation ofmicelles occurs in asolution of dissolvedsurfactant. It has been found thatsolubility at the Krafft point is nearly equal tocritical micelle concentration (CMC). Below the Krafft temperature, the maximum solubility of the surfactant will be lower than the critical micelle concentration, meaning micelles will not form. The Krafft temperature is a point ofphase change below which the surfactant remains incrystalline form, even in an aqueous solution. Visually the effect of going below the Krafft point is similar to that of going above thecloud point, with the solution becoming cloudy or opaque due to the surfactant molecules undergoingflocculation.
Surfactants in such a crystalline state will only solubilize and form micelles if another surfactant assists it in overcoming the forces that keep it crystallized, or if the temperature increases, thus causing entropy to increase and encouraging the crystalline structure to break apart.
Surfactants are usually composed of a hydrocarbon chain and a polar head group.
Increasing the length of the hydrocarbon chain increases the Krafft temperature because it improvesVan der Waals forces.
Moreover, since Krafft point is related to solid-liquid transition, better-packed polar heads within surfactant crystals increase Krafft temperature.[1]
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