Did you know that we develop guidelines for relating the colloidal stability of latexes to the ionic strength of the aqueous phase via the “critical coagulation concentration,” (CCC)? In our previous “Did You Know?” column, we included a schematic of the ion concentration around latex particles, which allowed us to mention the “diffuse double layer”. It is that halo around the particles that protects the latex from flocculation and eventual coagulation — we insert those images here for reflection.
So the question is, “How much ionic strength is too much?” This is quite interesting as it has been fairly common practice over the years to add some monovalent salts to the latex to reduce its viscosity (i.e. reduce the double layer width). But if too much salt is added — disaster! And remember that total ionic strength includes all ionic species including initiator, buffer, surfactant and adventitious metal impurities that may be in your source water.