Composition of pore surface investigated by positron annihilation lifetime spectroscopy

Temperature dependence of ortho-positronium lifetime in the mesopores of solids provides information about the electron density of the pore walls. This feature was used to determine the difference in electron density between the porous polymer XAD7HP and two kinds of porous polymer-silica composites prepared by swelling XAD7HP in a silica source and condensing it in both basic and acidic solutions. A higher amount of silica on the pore surface was found for the material prepared in basic conditions as compared to the one synthesized in the acidic solution. Taking into account the results of SEM, nitrogen sorption and 29Si MAS NMR, one can say that in acidic conditions silica penetrates the polymer micropores and condensates mostly between the polymer chains, while in basic conditions the penetration inside the pores is more shallow.

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► PALS provides information about the silica embedding place.
► Silica condenses mostly on the pore surface in composites prepared at basic condition.
► Silica penetrates the acid set composite matrix deeper than the basic set sample.
► Most of the initial XAD7HP pores remain empty in the composite materials.