Nanoporous Membranes Based On Surface-Modified Silica Colloidal Crystals

Silica colloidal crystals comprise a close-packed face-centered cubic (fcc) lattice of silica spheres of a sub-micrometer diameter with ordered arrays of nanopores.  The preparation of silica spheres is straightforward, the pore size in the colloidal crystals can be readily controlled by selecting the sphere size, and the silica surface chemistry is well developed.  Importantly, the diffusive flux of small molecules normal to the (111) plane of a semi-infinite colloidal crystal is only ca. 10 times smaller relative to the free solution value, independent of the size of the spheres used to assemble the crystal.  Thus, the rate of molecular transport remains significant, even when the pore size is reduced to the nanoscale to impart molecular transport selectivity.  All these above features make silica colloidal crystals ideal candidates for highly selective nanoporous membranes.  In 2005, we introduced, for the first time, the concept of permselective colloidal nanoporous membranes, and later developed a variety of responsive membranes based on silica colloidal crystals.  The present talk will describe our most recent results in size-selective transport through free-standing colloidal membranes, their surface modification with organic receptros, synthetic and biological polymers, and their responsive transport behavior as a function of pH and the binding of small molecules.