(182a) Fully-Coupled Modeling of Electrokinetic Flow and Migration in Microfluidic Devices Filled with Electrolytes

Nowadays, the miniaturization of mechanical and fluid mechanical components allows for the development of new innovative microsystems. Particularly in the field of (bio-)chemical analysis, there is a growing demand for rapid, precise and cheap methods. Hence, several concepts, e.g. ?lab on a chip? (LOC) or ?micro total analysis systems? (µTAS), have been introduced recently. The key to these concepts is the combination and integration of all process steps onto a single microfluidic platform. Typical process steps are pumping and mixing of liquids or the separation of solved species. Especially in microfluidic devices, electrokinetic effects are suitable to realize a multitude of these tasks. Moreover, it is obvious that, with respect to the design, simulations of the processes within such devices are useful. Thus, mathematical models that include the entire (multidisciplinary) range of the involved phenomena are required. The present study focuses on the flow and the species transport in a microchannel intersection, serving as an injector of a micro electrophoresis device. The intersection consists of a simple vertical (injection) channel and a horizontal (separation) channel. A typical scenario occurring in such a device is as follows. At the beginning, the microchannel geometry is filled with a homogenously-concentrated buffer electrolyte. To inject the sample to be analyzed, a potential difference is applied at the injection channel for a certain time. This drives the sample liquid into the injection channel until the junction is filled. Then, the potential difference is applied at the separation channel. The sample plug located within the junction is driven into the separation channel. During its transport the sample plug decomposes into its single components, constituting so-called concentration peaks. Finally, at the end of the separation channel, the peaks can be detected giving information about the component concentrations. The sample liquid consists of a mixture of ions, all solved in the buffer. Hence, the injection of the sample leads to a time-dependent concentration field, which influences the electrical field and the physicochemical properties of the channel wall. Moreover, chemical reactions take place during the transport at the front zone between sample liquid and buffer electrolyte.

We investigate the electrokinetic flow and the migration of all charged species by time-dependent and two-dimensional finite-elements-method (FEM) simulations. In order to consider all dominant features of this rather complex system, the electrical situation, the fluid dynamics, and the chemistry are taken into account.