(745e) Surface Modification Synthesis of Defect-Free Vertically Oriented Ordered Mesoporous Silica Membranes

Ordered mesoporous materials have highly ordered pore structure, well defined pore diameter in the mesopore range, high surface area and unique pore connectivities.  These materials in membrane morphology such that the pore channels are aligned perpendicular to the membrane surface are desirable as it will allow for better pore accessibility for use in a number of applications. To make defect free ordered mesoporous membranes with vertically aligned pores has been a major challenge for researchers working in this area.  In this paper, we will show that vertically oriented ordered mesoporous silica membranes can be synthesized as silica plugs filling the macron-sized straight pores of hydrophobic track-etched polycarbonate membrane support by an counter-diffusion self-assembly method.  However, these membranes have gaps between the mesoporous silica plugs and support pore wall.  We will report results of various methods studied to fill these gaps.  We found that these defects can be eliminated by filling the membrane gaps with an alkoxysilane followed by exposure to humid air to allow controlled hydrolysis and condensation resulting in formation of microporous silica within the gaps.   Molecular probing gas permeation and helium/nitrogen (or oxygen) binary separation tests, coupled with surface characterization methods, show that final membranes contain ordered mesopores of about 2.7 nm pore diameter, running through the membrane, with gaps sealed by microporous silica having a pore size less than 0.55 nm.   The results show that the liquid deposition technique is an effective way for defect sealing in counter-diffusion self-assembly method membranes and this approach could possibly be used in other systems with equal success.