In a study of Van der Waals forces between particles and surfaces, Electric double layer forces, DLVO forces, Polymer-mediated steric forces, and Depletion forces: 1. Derive an expression for the force between a sphere and a flat surface in terms of A, R. and D. 2. The Hamaker constants for most condensed phases interacting across a vacuum are on the order of 10-19 J. Why is this value so consistent across so many different kinds of materials? 3. In the synthesis of metallic nanoparticles, an oxidized metal salt is reduced to form the elemental metal. Why is poly(ethylene oxide) added to the synthesis of colloidal nanoparticles?