Soft matter, Fluidics and Interfaces

Transport phenomena near TiO2  surface 

Electro-osmosis represents the movement of fluid in contact with a solid under applied electric field. Since it involves current measurements based on ion transport, it can used to study the surface chemistry. It gives a direct measurement of zeta potential which is related to the surface charge. With this knowledge, the surface charge or zeta potential can be varied along the direction of electric field, and consequently the transport of different species across the boundary layer (i.e. solid-fluid interfaces) can be manipulated and controlled. As a starting point, different substrates like Silicon and Titanium dioxide have been chosen to understand it’s surface charge density through the corresponding zeta potential. 

Titanium Dioxide (TiO2 ) has been vastly studied as photo catalyst. TiO2 exhibits a change in surface charge upon irradiation of UV light due to the formation of electron-hole pairs. These pairs can then reduce/oxidize species adsorbed on the surface. Based on the relative rates of the reactions, an excess or depletion of charge can be generated at the surface. As a part of the student assignment, experiments have to be performed in order to quantify the generation and depletion of the various charged species at the surface, as a function of different parameters like the pH of solution, type of ionic species present in the solution and the ionic strength. It would also be interesting to visualise this effect under different conditions.

References:

[1]. Moorthy J, Khoury C, Moore J S, Beebe D; Active control of electroosmotic flow in microchannels using light, Sensors and Actuators B-Chemical, 2001, 75, 223-229

 [2]. Xuan Hao Lin, Yijia Miao , Sam Fong Yau Li, Location of photocatalytic oxidation processes on anatase titanium dioxide, Catal. Sci. Technol., 2017, 7, 441

[3]. Dileep Mampalli, Dirk van den Ende, Frieder Muge, A simple method to determine the surface charge in microfluidic channels, Electrophoresis 2010, 31, 563-569