High-strength microsphere preparations

The combination of high strength and electrical conductivity can be combined to produce highly novel phenomena. For example, in 1999 Lieber and co-workers prepared "nanotube nanotweezers". Two nanotubes were attached to independent electrodes and positioned near each other. When a voltage bias was placed across the two, the two nanotubes reversibly bent toward each other, fully mimicking the motions of a tweezer. These electrically activated tweezers can grab and manipulate polystyrene microspheres or silicon carbide nanoclusters. This early work could presage the development of true nanomachines that could perform unprecedented operations on a near-atomic distance scale. 

The polymer employed to prepare microspheres must be characterized in terms of molecular weight and purity,however this topic is beyond the scope of this article. Characterization of the materials may have implications for the formation of the microspheres. The viscosity and film-forming properties of the polymers used should be known. Viscosity can affect the tendency to form microspheres, their size, and even their shape. Burgess and coworkers have shown that albumin-acacia coacervates do not form microcapsules under certain conditions of pH and ionic strength, if the viscosity of the coacervate phase is too high. Burgess and Carless developed a method to predict the optimum conditions for complex coacer-vation based on the charge carried by the two polymers involved. 

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