Surfactants are amphiphilic molecules, meaning they have both a hydrophilic (water-soluble) part and a lipophilic (fat-soluble) part. Thanks to this dual nature, they play a key role in the formulation of many products, particularly foaming products, by reducing the interfacial tension between liquids and enabling the formation of stable foams. However, during the formulation of these products, cloudiness may occur due to poor solubilization of the surfactants, regardless of the presence of other ingredients that are difficult to mix (fragrances, oils, etc.). The turbidity of a surfactant system is directly linked to a solubilization defect, a major challenge for the quality and stability of formulations.
Solubility is a physical property of chemical compounds, depending mainly on the type of substance and the solution in which it is dissolved (the solvent). It is influenced, amongst other factors, by the temperature of the solution used and the pressure applied.
The mechanism of dissolution varies depending on the nature of the solute.
• In the case of ionic compounds, dissociation into ions plays a central role.
• For non-ionic compounds, the formation of hydrogen bonds between water molecules and the solute is predominant.
When considering surfactants specifically, there are several basic principles to bear in mind.
• The more ether groups (R O R) or groups capable of forming hydrogen bonds a surfactant molecule contains, the higher its solubility in water, due to increased hydrophilicity.
• As the temperature rises, solubility tends to decrease, which can cause the solution to become cloudy.
The cloud point is defined as the temperature above which two phases begin to separate in a solution, causing it to become heterogeneous; we will return to this later.
Coagulation and flocculation
In the form of micelles, surfactants, like any colloidal solution, can aggregate into larger clusters.
• Coagulation results in a …
