Microfluidic Pumping by Micromolar Salt Concentrations
Moving fluid around on the microscale is not as simple as taking a syringe off the shelf and pushing liquid through, because if you do this, things tend to break. In this talk, a colloidal ion-exchange-resin-based microfluidic pump is introduced and experimentally characterized. It operates in almost deionized water for periods exceeding 24h and effects fluid flows of um/s over hundreds of microns. This fluid flow displays a far-field, power-law decay which is characteristic of two-dimensional (2D) flow when the system is strongly confined in the vertical direction, and of three-dimensional (3D) flow when the system is less confined. Using theory and numerical calculations we show that our observations are consistent with electroosmotic pumping driven by umol/L ionic impurities in the sample cell, revealing the surprising impact of trace amounts of charge carriers. In addition, we explain how the power-law decay of the fluid flow can be understood on the basis of the confinement imposed by the sample cell. These two insights should benefit the design of a new class of microfluidic pumps that operate at low solute concentration.
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..