Is it possible to dilute your Ag nanoparticles in methanol or ethanol without risking agglomeration?

Our NanoXact and BioPure silver nanoparticles will not be perfectly stable in alcohols. The surfaces are not protected by any strong capping agents so they are quite sensitive to their environment. The stability will be determined by the relative water/alcohol ratio. I try to think of the stability and aggregation as a rate of change. The more pure the alcohol the faster the particles will aggregate and 'crash'. But that isn't to say that all particles will crash instantly. Particles can be stabilized with a variety of polymeric capping agents, but if you need the particles to be 'clean' or 'bare' your choices are much more limited.

What type of application are you looking to use the particles for? Is it for biological applications or for materials integration?

It's for material integration. We thought of an efficient way of spin-coating the Ag particles on a semiconductor. The problem with water is that it evaporates very slowly and leaves some stains on the substrate. A dissolution in ethanol would be easier to handle.

If the problem with water is having stains after drying, one solution could be to use purified material. If you are using as-synthesized silver nanoparticles there will be quite a bit of residual reactants left over in solution. If you can live with the slower drying I would recommend that.

Another option is to have a PVP coated silver (or some polymer capping agent). We can make PVP coated silver that is stable in alcohols, but I'm not sure if the polymer would cause more problems for your application or not.

What would be the thickness of such a polymer coating?

It is difficult to directly measure the polymer coating. With some calculations from microanalysis it appears that the coating may be up to ~4nm. But that will likely change with the solvent and also when dried.