AFM observation of small surface pores of hollow-fiber dialysis membrane using highly sharpened probe

Determining pore size distribution is important for characterization of a dialysis membrane. However, conventional microscopic techniques cannot present a sufficient image for determining pore size distribution. In the present study, tapping mode atomic force microscopy (TMAFM) has been shown to be a powerful tool for observing and evaluating the small surface pores of a hollow-fiber dialysis membrane. Sample fixing technique described below and a highly sharpened probe have made it possible to observe small pores on a soft and undulant surface of a dialysis membrane. This is the first time that clear TMAFM images of surface pores of a hollow-fiber dialysis membrane at such high resolution have been presented. Pore diameter was determined by image analysis. Average pore diameter of APS-150 (Asahi-kasei, Japan) determined by TMAFM was compared with those by field emission scanning electron microscopy (FESEM) and by the Hagen–Poiseuille equation. The average pore diameter of APS-150 determined by TMAFM was slightly higher than that by FESEM. The average pore diameter determined by the Hagen–Poiseuille equation was intermediate between values for that of inside and outside surfaces determined by TMAFM.