As we all know, the surfactants we add to synthetic latexes have allowed us to create wonderful nanoparticles and at the same time provide colloidal stability (against salts, freezing/thawing, and mechanical shear) to the dispersions. But they also can cause foaming problems when mixing and transporting the latexes, and remain in the final products causing potential water absorption problems in films and coatings. However, on a commercial scale, they are necessary.
Perhaps it goes without saying, but it should be obvious to us that the surfactants will be distributed between the water phase and the particle surface, and the question then arises as to what that distribution looks like. But first, are the surfactants also inside the polymer particles? For anionic or cationic surfactants, the answer is a resounding no. In fact, common anionic surfactants like sodium dodecyl sulfate (SDS, or SLS) are not even soluble in the monomers we use to make the polymer. Non-ionic surfactants present a different situation as some are soluble in the monomers we choose, but not usually soluble in the final polymers. This results in the potential condition that when non-ionics are added to a batch polymerization (lots of monomer in the particles), some of that surfactant might become absorbed inside the particle in the early stages of the polymerization, and perhaps get trapped within the particles in the latter part of the polymerization.