Cloud Point Control with Nonionic Surfactants: AEO and AES in Liquid Detergent Formulations

Buyers who specify ethoxylated fatty alcohols usually focus on active content and HLB value. In practice, a third number decides whether the finished liquid detergent stays clear on the shelf: the cloud point. It is the temperature at which an aqueous nonionic surfactant solution stops being transparent and starts to scatter light, and it is the single most useful predictor of storage stability for a formulation built on AEO or AES chemistry.

Why the cloud point appears

Ethoxylated surfactants hydrate through hydrogen bonds between water molecules and the ether oxygens of the polyoxyethylene chain. Those bonds are exothermic and weaken as temperature rises. At a certain point the hydration layer is no longer enough to keep the micelles dispersed, micellar aggregates grow, and the solution turns milky. Cool it down and the haze disappears, which is why the effect is reversible and why it should never be confused with a permanent phase separation caused by an unbalanced formula.

Two structural factors dominate. A longer ethoxylate chain raises the cloud point, because there are more binding sites for water. A longer alkyl chain lowers it, because the hydrophobic tail becomes harder to solubilise. This is why a C12 alcohol with 7 moles of ethylene oxide and a C16 alcohol with 7 moles behave very differently in the same base, even when the label says the same EO number.

Reading the numbers before you buy

For AEO-type products, the cloud point is normally reported as a 1 percent aqueous solution measured by the standard cloud point method, and the value is meaningful only together with the test concentration. A supplier that quotes a cloud point without stating concentration and electrolyte level has given you a number you cannot use. Detergent bases contain sodium chloride, sodium sulphate or citrate, and each of these salts shifts the cloud point downward, sometimes by more than ten degrees at realistic use levels.

The same caution applies to AES, the ethoxylated fatty alcohol sulphate. Here the cloud point of the pure active is less relevant than the behaviour of the neutralised, salted finished base, because the anionic sulphate head group changes the micelle charge and suppresses the salting-out effect to some degree. Formulators who blend AES with AEO usually find the blend more forgiving than either component alone.

Practical levers formulators use

The first lever is the ratio between nonionic and anionic surfactant. Increasing the anionic share generally pushes the cloud point up and improves oily soil removal at the same time. The second is the addition of a hydrotrope such as sodium xylene sulphonate or urea, which breaks up the liquid crystalline structures that cause gelling and raises the tolerable salt level. The third is chain length selection: moving from a C16 ethoxylate to a C12-C14 ethoxylate is often cheaper than adding hydrotrope and gives a cleaner viscosity profile.

Temperature of use matters as much as temperature of storage. A formulation with a cloud point of 45 degrees Celsius is comfortable in a European warehouse but marginal in a Southeast Asian distribution chain where a container can sit in direct sun. Buyers shipping to hot climates should specify a cloud point with a margin above the maximum expected ambient temperature, not just above room temperature.

What to put in the purchase specification

A workable specification lists the alkyl chain distribution, the ethoxylate mole number with its tolerance, the hydroxyl value or active content, the free fatty alcohol limit and the cloud point at a defined concentration in a defined electrolyte solution. Asking for the cloud point in deionised water alone tells you very little about how the material will behave in your base. Where possible, ask the supplier to quote the cloud point in a 1 percent solution containing 5 percent sodium chloride as a second reference point; the gap between the two values is a good indicator of salt sensitivity.

Moisture, pH and colour also belong in the specification. Ethoxylates can pick up residual catalyst and develop a yellow tint during storage, and a peroxide number above the agreed limit signals that the material has been exposed to air and heat for too long.

Where SINOFO fits in

SINOFO Group supplies refined glycerin, propylene glycol, fatty acids, fatty alcohols and their ethoxylated derivatives to formulators and distributors across Asia, Europe and the Americas. Our technical team works from the end formulation backwards, so specifications are set against the base you actually run rather than against a catalogue sheet. Grades, packaging and documentation can be matched to your market requirements, including COA, MSDS and country of origin statements.

If you are reviewing a nonionic surfactant specification or troubleshooting a haze problem in an existing base, send us the details of your system and we will come back with a practical recommendation. Inquiries are welcome at any stage of product development.