A quick and simple method to test silica colloids’ ability to resist aggregation

A simple freeze/thaw method to quickly test the ability of silica colloids against aggregation under different conditions is presented here. A solution of silica colloids, with size of about 50 nm, was immersed in liquid nitrogen for 1 min to force the aggregation of these colloids and then thawed at 60 °C for 10 min to room temperature. The dynamic light scattering (DLS) technique was used to measure the particle size both before and after the freeze/thaw (F/T) procedure to assess the silicaʹs ability to resist aggregation via size changes. Both the effects of pH and addition of polyvinyl pyrrolidone (PVP) were investigated here. Under alkaline condition (pH = 10), the silica colloid was more negatively charged and less PVP was needed to stabilize these silica colloids against this F/T test. However, when the pH was changed to 7.0, more PVP was needed to stabilize these silica colloids. When the pH was further lowered to acidic conditions (pH = 4), PVP lost its ability as a protective agent for the silica colloids, which aggregated immediately after the addition of PVP.