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Nanoscale Hetero-coagulation and Adsorption Phenomena: Magnetic Bone Mineral Abstract The Magnetic Bone Mineral demonstration was developed to provide students with a simple way to visualize nanoscale hetero-coagulation and adsorption phenomena. In this demonstration, aqueous suspensions of hydroxyapatite and magnetic nanoparticles are mixed together in a small clear container. The resulting suspension takes on a tan color intermediate between the initial magnetic nanoparticle and hydroxyapatite suspension. The most unique aspect of the hetero- coagulated nanoparticles is that the magnetic nanoparticle modified hydroxyapatite can be translated in solution under the influence of a magnetic field. This demonstration is suitable for all age groups from K-12 through college level and can be tailored to fit a number of curriculums due to the wide range of topics that can be incorporated into the demonstration (biomaterials, interaction potentials, colloid stability, magnetic phenomena, etc.).

Introduction The unique properties and unusual behaviors of nanoscale materials provide a driving force for a wide range of technologies. However, it is often very difficult to prepare effective educational demonstrations that illustrate nanoscale phenomena with a limited budget. The Magnetic Bone Mineral demonstration was developed to provide students with a simple way to visualize nanoscale hetero-coagulation and adsorption phenomena. Adsorption is a very fundamental nanoscale phenomena that plays a very important role in natural phenomena and science and engineering technologies. It is utilized in biological processes, catalysis, detergent applications, microelectronics, coatings and a wide variety of other processes. Hetero-coagulation is a term that describes particle/particle adsorption interactions involving two or more types of particles1, 2. These interactions are typically driven by electrostatic (opposite charges attract), chemical affinity effects, or size effects. In size based hetero-coagulation, nanoparticles seek to lower their surface energy by adsorbing onto larger particles. In this demonstration, magnetic nanoparticles are mixed with hydroxyapatite particles in suspension to allow visual observation of nanoscale heterocoagulation and adsorption interactions with the use of a strong magnet.

Procedure Synthesis of magnetic nanoparticles A solution containing a 1:2 molar ratio of Fe2+ to Fe3+ (typically 0.5 M FeCl3 and 0.25 M FeCl2, 50-100 ml) in de-ionized water was prepared and then slowly added to an ammonium hydroxide alkaline solution. The magnetic nanoparticle suspension was allowed to stir for 1 hour, washed via gravity sedimentation in the presence of a strong magnet or centrifugation to remove excess ammonium hydroxide, and stored in polypropylene bottles at room temperature.

Synthesis of Nanophase Hydroxyapatite In a typical reaction, equal masses of 1.00 molal (m) PO43- solution and the 1.67 m Ca2+ solution (500 grams each) were measured and the pH of each solution was adjusted to 10 by the addition of NH4OH. Five ml aliquots of the Ca2+ solution were sequentially added to the mechanically stirred PO43- solution. The pH of the precipitated hydroxyapatite slurry was maintained at 10 by the addition of NH4OH as needed. Precipitation reactions were performed in 1000 ml polypropylene bottles. The precipitate slurry was stirred for 1–3 hr after mixing

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Wilson, O. (2007, June), Nanoscale Hetero Coagulation And Absorption Phenomena: Magnetic Bone Mineral Paper presented at 2007 Annual Conference & Exposition, Honolulu, Hawaii. 10.18260/1-2--3076