Short answer: The CMC of SLS in pure water at 25 °C is about 8.2 mM, which is roughly 0.23-0.24% by weight. Above that concentration, additional surfactant goes into micelles and surface tension stops falling, while solubilising power keeps rising. The Krafft point, near 16 °C, is the temperature below which solubility drops sharply, which is why 30% liquid can paste up in cold storage or on winter routes.
What does the CMC tell a formulator?
Three things. Dosing below the CMC buys surface tension reduction, and dosing above it buys solubilisation, so pushing actives past the CMC has diminishing returns on wetting. Viscosity behaviour changes around micelle formation, which matters when you thicken with salt. And cost per unit of function stops improving once you are well past the CMC, which is why detergent formulas run 10-20% total actives rather than 40%.
Published values for SLS
| Property | Literature value |
|---|---|
| CMC in water, 25 °C | About 8.2 mM (0.23-0.24% by weight) |
| Surface tension at CMC | About 31-33 mN/m |
| Solubility in water, 25 °C | About 150 g/L |
| Krafft point | About 15-16 °C |
| Ross-Miles foam, 0.1%, 20 °C | About 180 mm initial (ASTM D1173) |
These are literature values for the pure surfactant in deionised water. Electrolytes, hardness and co-surfactants shift all of them, so confirm on your own system.
Why does the Krafft point matter commercially?
Because cold chains are real. A 30% liquid stored below its Krafft point can separate into a soft paste or precipitate, and a drum that leaves a warm warehouse for a winter route to Russia or Central Asia can arrive looking wrong. Keep liquid grades above 20 °C in storage, insulate the shipment, or switch the winter business to powder or needles, which do not have a solubility cliff. Labs running cold-room electrophoresis have the same problem and usually move to LDS, whose lithium counterion lowers the Krafft point. Our CMC and Krafft point guide covers the formulation side, and the freezing prevention article covers transport.
Key takeaways
- CMC of SLS is about 8.2 mM (0.23-0.24%) at 25 °C in pure water.
- Above the CMC you buy solubilisation, not lower surface tension.
- Krafft point near 16 °C is the cold-storage and winter-shipping constraint for 30% liquid.
- Literature values shift with hardness and electrolytes; verify on your own water.
For bulk pricing, MOQ and lead time on SLS 30% liquid, SLS 92% powder or LDS, request a quote through the contact page with your destination and storage conditions. If you are qualifying a grade for a winter route or a cold-room protocol, request a sample and request the COA and MSDS with solubility data for the lot. Contact our team and we will recommend the grade that fits your route.