The effect of supercritical fluid on morphology of polystyrene in gas assisted injection molding was studied,the SEM result showed that the morphology of polystyrene treated by supercritical fluid nitrogen gas was very different from that of untreated polystyrene.There was a laminar structure in treated polystyrene that induced by fountain flow when the melt was propelled by the gas in gas assisted injection molding.It was also found that gas penetration induced the occurrence of self similar structure,e.g.fractal structure which was related with viscosity finger effects.
