Electrophoretic mobilities of TiO2 colloids in an apolar solvent, toluene, were measured by differential-phase optical coherence tomography (DP-OCT). An electrode spacing of 0.18 mm, made possible by optical coherence tomography with transparent electrodes, enables measurement of the electrophoretic mobility with small samples (20 μL) of highly turbid colloids at low applied electric potential to avoid electrohydrodynamic instability and electrochemical reactions. In the presence of Aerosol-OT reverse micelles, which stabilized the countercharges, the zeta potential was positive for hydrophilic TiO2 (13 mV at 90 mM AOT) and negative for hydrophobic TiO2. The magnitudes of the zeta potentials were very similar for these two types of TiO2 and decreased at the same rate with AOT concentration. For both hydrophilic and hydrophobic TiO2, a general mechanism is presented to describe the zeta potential in terms of preferential partitioning of cations and sulfosuccinate anions between the particle surface and reverse micelle cores in bulk. This preferential partitioning is governed by the hydrophilicities and extents of the particle surfaces and reverse micelle cores, as a function of surfactant and water concentration. The emerging understanding of the complex charging and stabilization mechanisms for colloids in apolar solvents will be highly beneficial for the design of novel materials.

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Traditionally, finely dispersed metal catalysts have been formed by reduction of precursors within mesoporous supports. A new concept for designing catalysts with enhanced activities and selectivities is to infuse presynthesized nanocrystals with well-defined morphologies into ordered mesoporous materials. The decoupling of nanocrystal synthesis and infusion provides exquisite control of the nanocrystal size, morphology, and dispersibility within the pores. A dispersion of iridium nanocrystals was infused into mesoporous silica by expanding the solvent toluene with supercritical CO 2 . To achieve high nanocrystal loadings, up to 1.3 wt %, we tuned the solvent quality to strengthen the interactions of the nanocrystals with the pore walls, but without precipitating the nanocrystals in the bulk solvent. Z-contrast STEM indicates conclusively that the iridium nanocrystals were located within the pores and not on the external silica surface. High catalytic activity was observed for 1-decene hydrogenation, which is consistent with a high degree of dispersion of the 4.5 nm nanocrystals throughout the pores, as observed by TEM. A maximum turnover frequency (TOF) of 16 s -1 was measured, which was higher than the initial TOF for homogeneous catalysis with the same nanocrystals in 1-decene. The iridium catalysts do not require pretreatment to remove the tetraoctylammonium bromide ligands to achieve activation, as the ligands bind weakly to the iridium surface. Consequently, the activity was not enhanced when calcined at 500 °C in nitrogen or when annealed in supercritical CO 2 at 275 bar. The ability to predesign nanocrystal morphology and surface properties prior to infusion into the mesoporous silica support offers novel opportunities for enhanced catalyst activity, stability, and reaction selectivity.