Neck-size distributions of through-pores in polymer membranes

Capillary flow porometry (CFP) is used for measuring the most constricted part (bottleneck) of through-pores in synthetic membranes. In present work, a systematic study has been carried out to evaluate influence of membrane properties like tortuosity, intersecting pores and thickness on CFP. For evaluating CFP, the track-etched membranes were used as these membranes have cylindrical pores. The average, maximum and minimum pore diameters and pore-diameter distributions in the track-etched membranes were obtained by CFP, and compared with the values obtained by different techniques like atomic force microscopy (AFM), scanning electron microscopy (SEM) and molecular weight cut-off (MWCO). The internal architecture of pore in the track-etched membranes was studied by growing gold nano-rods in the pores. The gold nano-rods were grown in the membrane by electrodeposition using removable electrode (Hg). The transmission electron microscopy (TEM) of nano-gold rods were carried out after dissolution of the membranes in dichloromethane. The studies carried out in the present work showed that: (i) the CFP data remained practically independent of the membrane thickness and tortuosity, (ii) it measured the most constricted diameter of a pore independent of pore-architecture, and (iii) mean flow pore-diameters data were highly reproducible (±5%). The capability of CFP for assessing quality of the membrane was demonstrated using the pore-filled membrane samples having different amounts of the crosslinked poly-N-isopropylacrylamide (poly-NIPA). These samples were prepared by UV-initiator induced in situ photo-polymerization of NIPA in pores of the host microporous poly(propylene) membrane.