Paramagnetic silica particles: Synthesis and grafting of a silane coupling agent containing nickel ions onto colloidal silica particles

A method is presented for the preparation of stable model dispersions of paramagnetic silica particles. A specially designed silane coupling agent containing Ni2+ ions is grafted onto silica particles which are either commercially obtained or prepared by the Stober synthesis. A wet process is described which avoids aggregation of ungrafted and grafted silica particles. The resulting magnetic silica particles have been characterized by dynamic light scattering, transmission electron microscopy, elemental analysis, and infrared spectroscopy. Preliminary magnetization measurements and magnetic relaxation (NMRD) experiments illustrate some of the possibilities for studying model silica colloids with a covalently bonded paramagnetic surface layer.