A simple three step method for selective placement of organic groups in mesoporous silica thin films

• Selective functionalization of mesoporous silica thin films was achieved using a three step method.
• A volatile silane group is anchored by evaporation on the outer film surface.
• A second silane is deposited in the inner surface of the pores by post-grafting.
• Contact angle, EDS and XPS measurements show different proportions of amino groups on both surfaces.
• This method can be extended to a combination of silane chlorides and alkoxides functional groups.

Selective functionalization of mesoporous silica thin films was achieved using a three step method. The first step consists in an outer surface functionalization, followed by washing off the structuring agent (second step), leaving the inner surface of the pores free to be functionalized in the third step. This reproducible method permits to anchor a volatile silane group in the outer film surface, and a second type of silane group in the inner surface of the pores. As a concept test we modified the outer surface of a mesoporous silica film with trimethylsilane (–Si–(CH3)3) groups and the inner pore surface with propylamino (–Si–(CH2)3–NH2) groups. The obtained silica films were characterized by Environmental Ellipsometric Porosimetry (EEP), EDS, XPS, contact angle and electron microscopy. The selectively functionalized silica (SF) shows an amount of surface amino functions 4.3 times lower than the one-step functionalized (OSF) silica samples. The method presented here can be extended to a combination of silane chlorides and alkoxides as functional groups, opening up a new route toward the synthesis of multifunctional mesoporous thin films with precisely localized organic functions.

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