Hydrophilic TiO(2) particles made in a flame aerosol reactor were converted in situ to hydrophobic ones by silylation of their surface hydroxyl groups. So the freshly formed titania aerosol was mixed with a fine spray of octyltriethoxysilane (OTES) in water/ethanol solution and functionalized continuously at high temperature. The extent of functionalization and structure of that surface layer were assessed by thermogravimetric analysis (TGA) coupled to mass spectroscopy (MS), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and Raman spectroscopy. Product particles were characterized also by transmission electron microscopy (TEM), X-ray diffraction, and nitrogen adsorption. The influence of titania specific surface area (SSA) and OTES solution concentration on the functional group surface density was investigated. The titanium dioxide surface was covered with functional groups (up to 2.9 wt %) that were thermally stable up to 300 degrees C in air at an average density of 2 OTES/nm(2). Such surface-functionalized particle suspensions in 2-ethylhexanoic acid and xylene were stable over several weeks. In contrast, as-prepared hydrophilic TiO(2) precipitated within days in these solvents.
We investigate herein an interesting acoustic line-focused levitation mechanism, enabling the simultaneous transportation of the acoustically levitated particles. It is shown that the performance of such a system is strongly dependent on the envelope of geometric parameters of the levitator. To study this dependence systematically, a thorough numerical model using the finite element method is developed. Both rigid and flexural radiating plates are considered. The effect of all important geometric parameters on the resulting acoustic potential patterns is investigated. After successful experimental validation, in which particles of density ca. 1000 times higher than that of their surrounding gas (∼1 g/cm3 versus ∼10−3 g/cm3) are levitated and translated, the model proves to be reliable in predicting the position as well as the force exerted on the levitated particles.
We present herein a method for the acoustic translation of solid particles of waterlike density in air, by employing a single transducer and controlling the pressure field through regulation of the distance between the reflector and the radiating plate. The levitation and translation of polystyrene particles over a length of 37 mm (approximately 37 particle diameters) were experimentally demonstrated, numerically modeled, and explained. The results of the model show quantitatively how the acoustic pressure distribution inside the levitator chamber and the position of the potential nodes depend on the distance between reflector and radiating plate when the plate is driven in a flexural resonance mode. This phenomenon significantly extends the range of applications of acoustic levitation.
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