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.

No abstract

No abstract

No abstract

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.

Au and Pt nanoparticle distributions within hierarchically ordered mesoporous TiO2 were explored using a combination of techniques including ellipsometric porosimetry (EP) and X-ray photoelectron spectroscopy (XPS). EP studies were used to examine adsorbate-TiO2 interactions and the influence of adsorbate polarity upon adsorption isotherms for mesoporous TiO2 films with and without Pt and Au nanoparticles. In particular, methods are described for modeling EP data to estimate the surface area and porosity of mesoporous TiO2 films and for estimating the pore size distribution (PSD) directly from the ellipsometry parameters Psi and Delta when fitting parameters alone are unable to extract reliable optical constants from the ellipsometry data. This approach reveals that mesoporous TiO2 films of approximately 200 nm thickness and approximately 10 nm pore diameter can be loaded with 1.7 nm diameter Pt and 3.9 nm diameter Au nanoparticles up to 26 and 21 wt %, respectively. The BET surface area of a representative mesoporous TiO2 sample using toluene as the adsorbate was found to be 44 m2/g with a mean pore diameter of 8.8 nm. EP and XPS depth profiling experiments indicate that 1.7 nm diameter Pt nanoparticles are well dispersed through the mesoporous TiO2 film, while 3.9 nm diameter Au nanoparticles are concentrated at the top of the film, blocking a significant portion of the available TiO2 pore volume. UV irradiation of the TiO2 films indicates that adsorbate-TiO2 interactions and surface wetting effects can play a critical role in the resulting isotherm and in evaluation of PSD.

The aim of the present study was to develop and characterize a gastroretentive formulation for controlled drug release and to develop innovative gastro retentive formulation based on mucoadhesive patch systems using the solvent casting technique. Glipizide, an antidiabetic agent was used as model drug for formulating films. Mucoadhesive film was formulated using chitosan and HPMC K4M. PEG 400 was added as plasticizer in film preparation. 3 2 full factorial design was used to formulate the novel gastroretentive formulation. Amount of HPMC K4M(X1) and amount of chitosan (X2) was selected as independent variable while swelling index, folding endurance, mucoadhesion force and Q8 (% drug release after 8 h) was selected as dependent variables. The film with zigzag folding in the capsule was shown to unfold and swell under acidic conditions and provide controlled release of drug upto12 h in acidic medium. According to 3 2 full factorial design films, 9 batches were prepared and evaluated for surface pH, folding endurance, mucoadhesion force, drug content, in-vitro drug release etc. Surface pH of F1-F9 was in between 6.32 to 6.98. Thickness and % drug content for batch F1-F9 was found to be in between 0.236 mm to 0.289 mm and 95.42 % to 99.32 %, respectively. In-vitro drug release study of F1-F9 showed utmost 95 % drug release after 11 h. The results indicate that the dosage form is gastroretentive and can provide controlled release of drugs with narrow therapeutic window. Glipizide/ HPMCK4M / Chitosan (40:150:150) F8 was found to be optimized composition of mucoadhesive films that showed good swelling index, folding endurance, surface pH, mucoadhesion force, Q8 and % drug content.

A new concept is presented to form catalysts by infusion of presynthesized bimetallic nanocrystals into ordered mesoporous supports. For presynthesized FePt nanocrystals (<4 nm) coated with oleic acid and oleylamine ligands in toluene, high loadings above 10 wt % were achieved in 10 min. The strong metal−support interactions were favored by the low coverage of the weakly bound ligands. The nanocrystals were highly dispersed within the pores as indicated by HAADF-STEM and X-ray diffraction (XRD) and stable against sintering at 700 °C and desorption into polar and nonpolar solvents at room temperature. A phase transformation from a disordered phase (FCC) to ordered phase (FCT) was observed upon thermal annealing at 700 °C without sintering, as confirmed by convergent beam electron diffraction and XRD. The calcined FePt catalyst exhibited 6-fold higher catalyst activity (TOF = 30 s−1) than that of a commercial Pd-alumina catalyst for liquid 1-decene hydrogenation and was stable for multiple reactions. The decoupling of nanocrystal synthesis and infusion provides exquisite control of the nanocrystal size, alloy structure, binding to the support and dispersibility within the pores, offering broad opportunities for enhanced catalyst activities, selectivities, and stabilities.