Kulim KHT Krafft temperature & Cloud Point via CMC

Krafft Point Temperature
The Krafft temperature (also known as Krafft point, or critical micelle temperature) is
the minimum temperature at which surfactants begin to soluble (if the sample
concentration is below the CMC) and in some cases form micelles (if the sample
concentration is above the CMC).
Krafft point can be also regarded as the temperature at which micelles become
soluble (in the case of surfactant concentration is above the CMC value).
Below the Krafft temperature, there is no value for the critical micelle concentration
(CMC), i.e., micelles cannot form.
A surfactant with a low Krafft point is more soluble than a surfactant with a high Krafft
point.
The low Krafft point surfactant became insoluble at a concentration which was only
slightly lower than the CMC. By a slight increase in temperature the surfactant can
be further solubilized until the CMC is reached.
The Krafft temperature is a point of phase change below which the surfactant
remains in crystalline form, even in aqueous solution.
Surfactants in such a crystalline state will only solubilize if another surfactant assists
it in overcoming the forces that keep it crystallized, or if the temperature increases,
thus causing entropy to have a stronger force and encouraging the crystalline
structure to break apart.
Increasing the length of the hydrocarbon chain increases the Krafft temperature
because it improves Van der Waals forces.
Surfactants are effective at temperatures above their Krafft points.
Krafft Point Determination
The Krafft point can be estimated by measuring the temperature at which the
surfactant solution forms a clear solution (applies to all surfactant concentration
sample).
At this temperature the solubility of the surfactant becomes equal to the critical
micelle concentration. It is best determined by locating the abrupt change in slope of
a graph of the logarithm of the solubility against t or 1/T (applies to surfactant
concentration sample above CMC).


Cloud Point Temperature
Definition
• Anionics - is the temperature at which a product becomes turbid when it is
cooled under specified conditions.
• Nonionics - is the temperature at which a product becomes turbid when
heated.
Cloud points are characteristic of nonionic surfactants.
Cloud point may result in phase separation and instability.
Properties
• Anionics - The shorter the hydrophobic chain, the lower the cloud point of the
surfactant.
• Nonionics - The greater the degree of ethoxylation, the higher the cloud point.
Cloud Point Determination
Cloud points are typically measured using 1% aqueous surfactant solutions.
Anionics.
A neat surfactant sample is placed into a tube with a thermometer and then
immersed into an ice bath. The sample is cooled at a specified rate while stirred (to
provide even cooling). When the sample first begins to show slight hazing, the tube
is removed from the bath and inspected regularly. The cloud point is that
temperature at which the thermometer immersed in the sample is no longer visible
when viewed horizontally through the tube and sample.
Nonionics.
A 1% aqueous solution of a nonionic surfactant is heated at a specified rate and
monitored for haziness. The cloud point is the temperature at which the first haze is
observed.