Plot salt with and without the amide. A single viscosity number at one salt level does not describe the curve.
The peak is the specification
A SLES formula has a salt response curve. On the left, salt thickens. On the right, salt thins. CMEA shifts and often heightens that curve. Production that “always adds 1% salt” will overshoot the day the amide dose is corrected upward.
Esteem lists CMEA as the viscosity builder in shampoos. The certificate does not include your salt peak. That plot is the formulator’s job and should travel with the sample request.
Active level matters
Ten percent SLES active and fourteen percent do not share a curve. Diluting a concentrate in the plant moves the peak. Write the active in the bottle, not the as-sold paste level, unless you label it clearly.
Fragrance solubilizers and pearl esters also shift viscosity. Add them before you freeze the salt number.
A small map
Temperature of measurement must be fixed. A warm sample looks thinner and invites extra salt that is too much at 20 °C.
Sulfate-free bases do not follow this curve. Do not import a SLES salt target into a glucoside or sulfosuccinate chassis.
| Change | Usual viscosity effect | Check |
|---|---|---|
| More CMEA | Thicker at lower salt | Haze |
| Salt past the peak | Thinner | Do not add more salt |
| More CAPB | Milder, different peak | Not a 1:1 amide swap |
| Lower SLES active | Weaker salt response | Replot |
How salt and CMEA grow the same micelles
SLES head groups repel each other. In dilute salt the micelles stay small and the shampoo pours like water. Added sodium chloride screens that repulsion, the micelles lengthen into rods, the rods entangle, and viscosity climbs. CMEA joins the micelle and encourages the same rod growth, so the climb starts at less salt and often reaches a higher peak.
The right-hand side of the curve is the part production misses. After the peak, extra salt does not create a thicker shampoo. The micelles change shape again and the viscosity falls. A plant that “always adds 1% salt” will overshoot on the day the amide dose is corrected upward. The specification is the peak, not a single viscosity at one salt level.
Active matter moves the whole curve
Ten percent SLES active and fourteen percent do not share a curve. A concentrate diluted in the plant moves the peak even when the amide percentage on the batch sheet looks unchanged. Write the active in the bottle. CAPB, fragrance solubilizers, and pearl esters move it again. Freeze the salt number only after those are in the formula.
CAPB is not a quiet extra. It changes mildness and the peak position. Many chassis use a low CMEA level and a low CAPB level together. Replacing one with the other one-for-one copies neither the foam film nor the salt curve. LAS dish liquids have a related shape and different numbers. Plot the surfactant you actually fill.
A reading that falls after more salt
If viscosity fell when salt was added, the batch is past the peak. More salt will not recover it. Reduce salt, or reduce amide, and replot. Adding CMEA to “bring it back” usually pushes the peak further left and the next salt addition fails the same way.
Measure at a fixed temperature. Then check haze at the cold-storage temperature, because the amide level that built the peak may be the level that clouds. Sulfate-free bases do not follow this curve. A SLES salt target imported into a glucoside or sulfosuccinate chassis will not land.
How to Specify with Esteem
- Fix SLES active and CAPB if it is present.
- Run a salt curve at two CMEA levels.
- Mark the peak, not only the rising side.
- Add fragrance after the curve is known.
- Do not chase a low reading with more salt if you are past the peak.
See viscosity builders and the alkanolamide foam article.