Nonionic Surfactant Technical Guide
Cloud point is the temperature at which a solution of certain nonionic surfactants develops visible turbidity as dissolved material begins to separate into another phase.
Check the exact grade, concentration, test medium and method before comparing two reported temperatures.
Meaning and boundaries
Why Ethoxylated Nonionic Surfactants Become Cloudy
An ethoxylated nonionic surfactant contains a water-compatible polyoxyethylene chain and a more oil-compatible hydrophobic group. In aqueous solution, water associates with the ethylene oxide units. As temperature rises, hydration becomes less favorable and the balance among the surfactant, water and dissolved ingredients changes. The initially uniform solution can separate into a surfactant-rich phase and a water-rich phase, producing visible turbidity. In suitable systems, cooling reverses the transition and restores clarity. This phase description is reported for selected linear alcohol ethoxylates in Li, Bai and Chen, Colloids and Surfaces A.
This model does not predict every nonionic surfactant. Some materials do not show a measurable cloud point within a particular method’s temperature and composition window. ASTM D2024-09(2023) is limited to specified systems with a sharp visible change under its concentration, water and temperature conditions. ISO 1065:1991 covers EO-derived and mixed nonionic surface-active agents and specifies five methods. Its abstract states that Methods D and E require agreement between the parties concerned.
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| Term | What changes | How to use it |
|---|---|---|
| Cloud point | An aqueous or specified test solution becomes visibly turbid as phase behavior changes | Compare only with the same material identity, concentration, medium, method and endpoint |
| Melting point | A material changes between solid and liquid states | Use for physical handling or phase-state questions, not as a substitute for aqueous cloud point |
| Pour point | A liquid reaches a defined low-temperature flow limit under a stated test method | Use for low-temperature handling, not aqueous surfactant phase separation |
| Krafft point | Surfactant solubility rises sharply and becomes equal to the critical micelle concentration | Apply to solubility and micelle-formation questions; see the IUPAC definition |
HLB is not a cloud-point test. It describes hydrophilic and lipophilic balance, whereas cloud point records an observed transition under stated conditions. Do not substitute an HLB value for an exact-grade cloud-point measurement.
Procurement comparison gate
Compare Four Test Fields Before You Compare Two Numbers
A cloud-point number without its test basis is incomplete procurement data. Pass both values through the same four-field gate before treating a difference as a grade difference.
Exact material identity
Confirm the product name, chemistry and grade. Carbon-chain distribution, ethoxylation distribution and blended composition can affect the observed transition. A family name such as “alcohol ethoxylate” is not enough.
Surfactant concentration
Record the concentration and whether it is expressed by mass or another basis. A study of three linear alcohol ethoxylates found concentration-dependent cloud points, so do not compare a 1% result directly with an unstated or different concentration.
Test medium
Identify deionized water, an electrolyte solution, a glycol-containing medium or another defined mixture. Additive identity and concentration can change the result in studied systems.
Method and endpoint
Record the named standard or internal method, heating or cooling direction, and visual or instrumental endpoint.
Why the medium matters
Technical grade tables may report separate water, salt-medium and other-medium values, as illustrated in the Sasol MARLIPAL technical data. Do not treat these values as interchangeable.
Why the method matters
ASTM D2024-09(2023) is limited to 0.5% to 1.0% systems in deionized water, between 30°C and 95°C, with a visible transition within 1°C. ISO 1065:1991 specifies five methods with different applicability conditions. The official GB/T 5559-2010 record identifies the current Chinese standard for EO-derived and EO/PO block nonionic surfactants.
Buyer checklist
- Exact grade and current document revision
- Concentration and preparation basis
- Full test-medium composition
- Method, endpoint and heating or cooling direction
- Specification limit or range
- Batch result and lot number for a COA review
If one field differs or is missing, treat the figures as separate observations until the test bases are aligned.
Evidence-labelled examples
Read a Specification Range and a Batch Result Differently
A specification defines the acceptance limits stated for a grade. A batch COA records the result obtained for one identified lot. The batch result shows where that lot fell within the stated specification, but it does not replace the range or establish one fixed value for every future lot.
The following figures come from the Kemaix batch COA records accepted as source material for this article. Each number remains attached to its evidence type and stated test basis.
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| Grade | Documented specification | One batch result | Lot | Medium and concentration | Stated method |
|---|---|---|---|---|---|
| AEO-7 | 50 to 70°C | 56.5°C | KM20260212001 | 1% aqueous solution | GB/T 5559 |
| AEO-9 | 80 ± 3°C | 82.2°C | KM20260108003 | 1% aqueous solution | GB/T 5559 |
Both COAs state a 1% aqueous solution and GB/T 5559. The official GB/T page identifies the method standard and scope, but it does not verify Kemaix product data. The lot results above come only from the Kemaix COAs.
The two rows share a stated concentration and method, which supports a document-level comparison. This does not establish interchangeability in the buyer’s formulation. Review the other exact-grade acceptance items and formulation test results separately.
For purchasing, request the current TDS, SDS or MSDS and batch COA for the exact grade and order. Document availability must be confirmed. Do not transfer these figures to another AEO or EL grade. Neither batch result proves detergency, wetting, foam behavior, compatibility or finished-formula stability.
Use the comparison to start a grade review. Your operating conditions and complete formulation determine the next test.
Formulation validation
Use Cloud Point to Design a Screen, Not to Predict the Finished Formula
Cloud point can help screen the phase behavior of a documented ethoxylated nonionic surfactant under a stated composition and method. It cannot, by itself, predict the performance of a cleaner, textile auxiliary or other industrial formulation.
Concentration and electrolytes
Changing surfactant concentration can change the measured transition. Ion identity and level can also produce different effects, including increases or decreases in cloud point.
pH and dissolved ingredients
Record the complete chemical environment instead of assuming that a water-only result applies.
Hydrotropes, co-solvents and surfactants
These materials can change solubility and phase behavior. Ionic or nonionic co-surfactants can shift the transition through mixture interactions.
Operating temperature
Record heating and cooling history, hold temperature and observation point against the intended process and acceptance criterion.
Li, Bai and Chen found concentration-dependent behavior and different responses to salts, ionic surfactants, polymers and alcohols in three selected linear alcohol ethoxylates. The direction and magnitude depended on the tested system, so their results do not provide a generic correction factor. See Effects of additives on the cloud points of selected nonionic linear ethoxylated alcohol surfactants. A 2026 experimental and thermodynamic study of selected ethoxylated alcohols also reports that electrolyte effects depend on ion identity and ethoxylation; see the Journal of Chemical & Engineering Data study.
A three-stage validation ladder
- Review reported data. Align grade identity, concentration, medium, method and endpoint. Set aside direct comparisons when a field is missing.
- Repeat a controlled aqueous screen when relevant. Use the same defined method and preparation for every candidate. Record replicate results, the temperature path and the observation rule. This stage checks comparability, not finished-product performance.
- Test the complete formulation. Add the real builder package, electrolytes, pH adjustment, solvents, hydrotropes, other surfactants and relevant process sequence. Run the actual temperature range and storage conditions. Apply buyer-defined acceptance criteria for clarity, phase behavior, foam, wetting, detergency or other required functions.
Cloud point is one selection input. It does not prove cleaning efficiency, wetting speed, foam control, compatibility, shelf stability or use suitability. Test those properties in the complete formulation and process. Kemaix can review candidate identity and available exact-grade documents against the conditions you provide. The customer’s validation program determines final formulation approval.
Technical FAQ
Cloud Point FAQ and Exact-Grade Review
Does a higher EO level always mean a higher cloud point?
No universal rule applies. Within a related series under aligned test conditions, additional ethoxylation can increase hydrophilicity and may raise the accessible cloud point. Alkyl distribution, EO distribution, concentration, medium and method can change the result. Compare current exact-grade data under the same basis.
Do salts always lower the cloud point of a nonionic surfactant?
No. The effect depends on the ion, concentration and complete composition. Research on selected linear alcohol ethoxylates reports both increases and decreases with inorganic salts. Test the actual electrolyte package instead of applying one universal rule.
Why do two suppliers report different values for similar grades?
The materials may differ, or the concentration, medium, method and endpoint may not match. Ask for all four fields before attributing the difference to product quality. Compare a specification range and one lot’s COA result as different evidence types.
Is cloud point the same as HLB?
No. HLB describes hydrophilic and lipophilic balance. Cloud point records an observed transition under defined conditions. Use both as screening inputs where relevant, but do not calculate one as a substitute for the other.
Should my process operate below the reported cloud point?
There is no universal operating rule. The answer depends on whether clarity or a particular phase state is required and on how the complete formula behaves during processing, use and storage. Test the actual formulation across its defined temperature cycle.
Can Kemaix provide documents and a sample?
Kemaix can check current TDS, SDS or MSDS and batch COA availability for the exact product and order. Free 200 to 500 g samples may be available with the corresponding COA, subject to exact-grade confirmation. Standard products can be supplied from 200 kg, subject to grade and order confirmation.
Send Your Process and Document Requirements
Include the following information in your inquiry:
- target grade or chemistry
- use concentration and full medium or formulation type
- operating, filling, storage and use temperature range
- electrolytes, builders, pH, hydrotropes, solvents and other surfactants
- required function and acceptance criteria
- destination market and intended application
- requested quantity
- required TDS, SDS or MSDS, batch COA or other exact-grade documents
What Kemaix Checks Next
Kemaix will review exact-grade identity, current document availability, candidate availability and sample options. For customization requests, Kemaix can review EO/PO ratio, molecular weight, HLB and cloud point for adjustment, subject to project-specific feasibility.
Kemaix does not infer finished-formula suitability from cloud point alone. Confirm the selected material in your laboratory or production process under actual conditions.
