Patterning Porous Oxides within Microchannel Networks

Nature abounds in hierarchical structures that are formed through highly coupled and often concurrent synthesis and assembly processes over both molecular and long-range length scales. The existence of these structures such as abalones and diatoms has both biological and evolutionary significance. It has been a long-sought goal to mimic the natural processes responsible for these exquisite architectures using so-called biomimic strategies to control the structural organization. Several approaches are currently available for the preparation of ordered structures at different length scales. For example, organic molecular templates can be used to form zeolitic structures with ordering lengths less than 3 nm; mesoporous materials with ordering lengths of 3±30 nm can be obtained through inorganic/organic cooperative assembly using surfactants or amphiphilic block copolymers as the structure-directing agents; the use of latex spheres affords macroporous materials with ordering lengths of 100 nm±1 lm; and soft lithography can be used to make high-quality patterns and structures with lateral dimensions of about 30 nm to 500 lm. Recently, we demonstrated that by carrying out specific self-assembly processes within a microchannel network, it is possible to create porous structures that are ordered over multiple length scales (Fig. 1). These self-assembly processes include colloidal crystallization and surfactant templating. As a result, microporous, mesoporous, and macroporous materials can be directly patterned on the substrates. This article reviews recent progress in the synthesis, characterization, and potential applications of these patterned porous materials.