2.3. Experimental setup and signal acquisition
Fig. 1. Experimental setup.Figure optionsDownload full-size imageDownload as PowerPoint slide
3. Results and discussion
3.1. Mechanism and characteristics of flow PF-562271 based on the tungsten oxide electrode
The tungsten oxide electrode has a bilayer structure consisting of a compact inner layer of WO3 and a loosely bound outer hydrated layer of WO3·xH2O. Lillard et al.  has reported a corresponding decrease in the thickness of the surface layer under the hydrodynamic effect, our previous work also demonstrated a dramatic and positive change in the open circuit potential of the tungsten oxide electrode under the hydrodynamic effect .
In order to investigate the mechanism of flow sensor, the change of potentials were measured for the flow velocity of 1.6 mm/s in solutions of different pH which contain the point of zero charge (pzc). The experimental result is seen in Fig. 2. When the tungsten oxide electrode was immersed in the solution of pH above the point of zero charge, tungsten oxide sensor surface was charged negatively. A flow induced streaming potential at the solution/electrode interface comprising deprotonated terminal hydroxyl groups from the hydrated tungsten oxide. Therefore, the potential of tungsten oxide electrode would shift positively in the flowing fluid. However, the potential of tungsten oxide electrode would shift negatively in the solution of pH below pzc as the terminal hydroxyl groups of the hydrated oxide surface become protonated. The experiment strongly suggests that potentiometric response behavior induced by flow was based on streaming potential.