Mesoporous Silica Micromotors with a Reversible Temperature Regulated On-Off Polyphosphazene Switch.

The incorporation of an extraneous on-off braking system is necessary for the effective motion control of the next generation of micrometer-sized motors. Here, the design and synthesis of micromotors is reported based on mesoporous silica particles containing bipyridine groups, introduced by cocondensation, for entrapping catalytic cobalt(II) ions within the mesochannels, and functionalized on the surface with silane-derived temperature responsive bottle-brush polyphosphazene. Switching the polymers in a narrow temperature window of 25-30 °C between the swollen and collapsed state, allows the access for the fuel H2 O2 contained in the dispersion medium to cobalt(II) bipyridinato catalyst sites. The decomposition of hydrogen peroxide is monitored by optical microscopy, and effectively operated by reversibly closing or opening the pores by the grafted gate-like polyphosphazene, to control on demand the oxygen bubble generation. This design represents one of the few examples using temperature as a trigger for the reversible on-off external switching of mesoporous silica micromotors.