Cloud point is an important property to consider when evaluating surfactants for your formulation.
Cloud point is defined as the temperature above which a surfactant rich phase separates from an aqueous solution. This separation occurs when a nonionic surfactant, for instance, becomes insoluble due to increased heat, resulting in a cloudy or hazy dispersion in the solution. As heat and instability increases, the solution may undergo total phase separation.
It is generally understood that nonionic surfactants will perform most effectively when used at temperatures at or near their cloud point.
With this in mind, it is possible to manipulate the cloud point of a solution through the presence of other materials. More specifically, certain components can depress or increase the solution’s cloud point. For example, the addition of a coupler or hydrotrope can increase the cloud point of a solution, whereas builders or other salts (electrolytes) will depress the cloud point temperature. In fact, different salts will result in varying depression rates of a surfactant’s cloud point.
Cloud point and water solubility increase as the ethylene oxide (EO) content of a particular surfactant increases. Conversely, cloud point will decrease with increasing alkyl carbon chain length. As such, when the carbon chain length of a molecule increases, a greater number of moles EO must be added to maintain the same cloud point for the surfactant.
In short, understanding cloud point and how to adjust this property through tools such as surfactant selection and hydrotrope integration can assist in tweaking, stabilizing and optimizing a formulation’s performance.