RELATIONSHIP BETWEEN PORE STRUCTURE AND DIFFUSION TORTUOSITY OF ZRO2 COLLOIDAL AGGREGATES

The performance of chromatographic materials is extremely sensitive to variations in pore architecture. In this study, porous zirconia parti cles (5-10 mum) manufactured with an oil emulsion process have been ch aracterized with the aim of explaining its success in protein separati ons with liquid chromatography (HPLC). Its chromatographic performance is surprising since it is an aggregate of colloidal spheres; if the s pheres are near close packed, small constrictions in the pore network should drastically reduce the effective diffusion coefficient and thus diminish the chromatographic resolution of proteins. Moreover, if sma ll constrictions are avoided, such materials may serve as catalyst sup ports requiring reaction of large molecules (e.g., block copolymers). To characterize the pore structure we use electron microscopy, SEM and TEM; nitrogen adsorption; and mercury porosimetry. Since the latter t echniques are compromised by the presence of pore constrictions, we al so use the NMR spin lattice relaxation and NMR self diffusion experime nt to determine the average hydraulic diameter and tortuosity of the p ore space. It is shown that while many small constrictions are present , the spheres are quite loosely packed. There is still a high degree o f connection between pore spaces through larger constrictions than wou ld be expected for close packed spheres. The particles are very porous and the effective tortuosity for diffusion is surprisingly low. (C) 1 994 Academic Press, Inc.