What is cloud point? Why is it important?



Cloud point is the temperature above which an aqueous solution of a water-soluble surfactant becomes turbid (see photograph below). Knowing the cloud point is important for determining storage stability. Storing formulations at temperatures significantly higher than the cloud point may result in phase separation and instability. Wetting, cleaning and foaming characteristics can be different above and below the cloud point. Generally, nonionic surfactants show optimal effectiveness when used near or below their cloud point. Low-foam surfactants should be used at temperatures slightly above their cloud point.

Cloud points are typically measured using 1% aqueous surfactant solutions. Cloud points range from 0° to 100°C (32 to 212°F), limited by the freezing and boiling points of water. Cloud points are characteristic of nonionic surfactants. Anionic surfactants (with negatively charged groups) are more water-soluble than nonionic surfactants and will typically have much higher cloud points (above 100°C). The presence of other components in a formulation 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 will depress the cloud point temperature.

For low-foam applications, the cloud point of the product should be just below the use temperature. For example, the cloud point of TRITON CF-32 defoamer is 23°C (73.4°F). This defoamer should be used around 25-28°C (77-82°F) for maximum efficacy. For standard foam applications, the cloud point of the surfactant should be just above the use temperature. For example, the cloud point for TRITON X-100 surfactant is 66°C (150°F). This surfactant should be used at <66°C (150°F).

Water solubility of a nonionic surfactant/defoamer varies inversely with temperature. A solution of TRITON CF-32 defoamer is clear at 20°C but is cloudy at 40°C.

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