there is no little black bits which i found forming in the one made with glucose, making me believe it was the glucose potentially spoiling which was causing these black flex's?
Yes, and no.
If I fill a beaker with distilled water and I ask you what is in it, what would you say? Most people would say its just a jar of water and for most people, that answer is good enough.
However its not technically accurate. In the beaker is the bulk water, but along the sides of the beaker is a layer of water that is different. Its more structured, with several layers of water molecules that are lined up. Then there is the surface of the water which is also different and this difference causes surface tension. In the bulk water, every molecule is surrounded by other molecules, which causes the attractive forces on the molecule to cancel out to zero. The top layer of water molecules is not surrounded by other water molecules, so the attractive forces do not cancel. Because of this and the fact that the metal particles are covered in stabilizer molecules, the concentration of silver nanoparticles is greatest at the top layer of water. If the concentration is higher than the stabilizer layer on the nanoparticles can withstand, the nanoparticles will agglomerate in the top layer of the water causing little floating islands of metal particles.
