Observation of polymer membrane surface in water by atomic force microscopy

Surfaces of porous polycarbonate (PC), porous polytetrafluoroethylene (PTFE), poly (vinyl alcohol) (PVA) gel and regenerated cellulose (RC) gel membranes are observed in water by atomic force microscope (AFM). PC surface images by direct contacting (DC) mode showed an elevation around a pore. On the other hand a lot of blind pores of 10 nm to 40 nm of height and 150 nm to 400 nm of diameter on the surface were observed by alternative contacting (AC) mode. For PTFE surface images by AC mode we could not find the pore size difference between the membranes whose average pore sizes are about 0.4 mu m and 1.5 mu m determined by a bubble point method and we could observe the air bubble enclosed in the pore. PVA gel membrane surface images by AC mode shows the bright bands caused by the replica of scratches on the membrane cast plate, and the undulation structure covering the surface. RC gel membrane surface image by AC mode shows the light and shade stripes corresponding to the machine elongation direction.