Effect of polyvinyl pyrrolidone molecular weights on the formation of nanosized silver colloids

Polyvinyl pyrrolidone (PVP) of three different molecular weights (MW=8000, 29,000, 55,000) were tested in this work for their ability to stabilize silver colloids obtained from chemical reduction by formaldehyde. Our results indicated that their effects against agglomeration would depend to a great extent on the alkaline used for the promotion of reduction reaction at ambient temperature. When NaOH was used, the reaction rate was very fast and hence only PVP with large molecular weight could produce silver colloids of sizes around 20 nm. On the other hand, when Na2CO3 was used, the reaction path was significantly changed and slowed down as well. Under this circumstance, PVP with MW of 8000 offered the best protection against agglomeration. It could produce silver colloids of only 5 nm and the size distribution was nearly uni-modal. After a proper washing process, much of PVP could be removed. The sintering behavior of those washed silver colloids was then briefly studied.