Effect of solids concentration on TiO2/Ni composite foams prepared by aqueous gelcasting of particle-stabilized emulsions

Porous TiO2/Ni composite foams were prepared from sintering of gelcasted particulate emulsions; in which, surface of the initially hydrophilic TiO2 nanoparticles was hydrophobized through selective adsorption of benzethonium chloride. The adsorption led to a preferential deposition of the TiO2 particles at the air-water interface to stabilize the emulsions upon mechanical frothing. The remaining TiO2 and hydrophilic Ni particles would reside between the emulsion bubbles to form scaffolding struts, together with addition of agar as shape-setting agent by freeze gelcasting. Sintered foams with a porosity of 66-79% and a multi-modal pore-size distribution were obtained without phase segregation. Three-point rupture strength increased from 175 to 760 kPa as the solids concentration was increased. Electrical resistance yet decreased by more than 62% as the solids concentration exceeded 7 vol%, revealing that the increased cell-wall thickness would facilitate formation of percolative Ni network for electrical conductance when the solids concentration was increased.