Abstract
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 silica's 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. © 2014 Elsevier B.V.