Novel approaches for optimized powder processing of advanced ceramics are reviewed with an emphasis on directcasting methods and solid freeform fabrication techniques. The fundamental principles for green body formation are discussed; a distinction is made between physical and chemical gels based on the nature of the induced gelation. An overview of the properties of dense suspensions is presented, with a focus on the factors controlling the maximum solids loading. Recent work on direct measurements of interparticle forces in ceramic systems is presented and related to rheological properties.

In this work, the synthesis and physiochemical characterization of titanium oxide nanoparticle-graphene oxide (TiO 2 -GO) and titanium oxide nanoparticle-reduced graphene oxide (TiO 2 -RGO) composites was undertaken. TiO 2 -GO materials were prepared via the hydrolysis of TiF 4 at 60 °C for 24 h in the presence of an aqueous dispersion of graphene oxide (GO). The reaction proceeded to yield an insoluble material that is composed of TiO 2 and GO. Composites were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, N 2 adsorption-desorption, and thermal gravimetric analysis/differential thermal analysis (TGA/DTA). This approach yielded highly faceted anatase nanocrystals with petal-like morphologies on and embedded between the graphene sheets. At higher GO concentrations with no stirring of the reaction media, a long-range ordered assembly for TiO 2 -GO sheets was observed due to self-assembly. GO-TiO 2 composites formed colloidal dispersions at low concentrations (∼0.75 mg/mL) in water and ethanol but were not amenable to forming graphene papers via filtration through Anodisc membranes (0.2 µM pore diameter) due to their high titania concentration. Zeta potential measurements and particle size distributions from dynamic light scattering (DLS) experiments on these materials explain the stability of the TiO 2 -GO colloidal solutions. Chemical and thermal methods were also used to reduce TiO 2 -GO to give TiO 2 -RGO materials.

The movement of a liquid droplet on a flat surface functionalized with a photochromic azobenzene may be driven by the irradiation of spatially distinct areas of the drop with different UV and visible light fluxes to create a gradient in the surface tension. In order to better understand and control this phenomenon, we have measured the wetting characteristics of these surfaces for a variety of liquids after UV and visible light irradiation. The results are used to approximate the components of the azobenzene surface energy under UV and visible light using the van Oss-Chaudhury-Good equation. These components, in combination with liquid parameters, allow one to estimate the strength of the surface interaction as given by the advancing contact angle for various liquids. The azobenzene monolayers were formed on smooth air-oxidized Si surfaces through 3-aminopropylmethyldiethoxysilane linkages. The experimental advancing and receding contact angles were determined following azobenzene photoisomerization under visible and ultraviolet (UV) light. Reversible light-induced advancing contact-angle changes ranging from 8 to 16 degrees were observed. A large reversible change in contact angle by photoswitching of 12.4 degrees was achieved for water. The millimeter-scale transport of 5 microL droplets of certain liquids was achieved by creating a spatial gradient in visible/UV light across the droplets. A criterion for light-induced motion of droplets is shown to be consistent with the response of a variety of liquids. The type of light-driven fluid movement observed could have applications in microfluidic devices.