Sodium stearate forms associated colloids

Soaps and detergents behave like true solutions at low concentrations but form colloids above Critical micelle concentration(CMC) which is 10^-4M-10^-3M due to association is sodium stearate(soap) C₁₇H₃₅ part is Hydrophobic(nonpolar) part(tail) COO-part is Hydrophilic(polar) part(head).

At low concentration;C₁₇H₃₅COO-Na+ ions present on surface with COO- groups in water and C₁₇H₃₅ chains staying away and remain at the surface At or above CMC the polar part (or) the anion part ( COO-)  are pulled into the bulk  where they aggregate to form spherical shape with the C₁₇H₃₅   part(non polar) towards the center of the sphere and COO- part remaining outward on the surface of the sphere, Micelles are formed due to association above CMC   

The Hydrophobic part dissolves the grease deposit and  hydrocarbon chain is hydrophobic , anionic part is hydrophilic