Sodium oleate is the sodium salt of oleic acid. What is oleic acid or salt in your question? In M9 there are many different salts. With these salts, oleic acid will be neutralized. Insoluble salts can also be obtained. Sodium oleate is itself a surfactant and therefore no use of other surfactants is required. Tergitol NP-40 or tween create a foam. Silicone polymers reduce foam.