http://www.cd-bioparticles.com/p/DiagNano™-NR3-Silica-Particles-20-μm_258_262_291_3798.html20 µm silica particles are available with alkylammonium (NR3+) groups on the surface and supplied in water without any surfactants. They display a constant positive zeta potential of +40 mV across the entire pH scope ranging from 2 to 10.