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Application of Charged Membranes in Electroosmotic Pumping

Prakhar Prakash1, Andrew Zydney1, Michael D. Grissom2, and Christopher D. Rahn2. (1) Chemical Engineering, Pennsylvania State University, University Park, PA 16802, (2) Mechanical Engineering, Pennsylvania State University, University Park, PA 16802

Electroosmotic pumps can be an attractive alternative to other pumping systems since they involve no moving parts and operate without any mechanical noise. This is of particular interest for stealth operation in certain military applications. The objective of this work was to develop a high performance electroosmotic pump for actuation of a Flexible Matrix Composite (FMC) tube containing two families of oriented stiffening fibers which is able to provide high strain and block force.

Electroosmotic pumps were designed using various inorganic membranes made of 99.99% Silica or Alumina. The pump characteristics were evaluated as a function of the membrane pore size, applied voltage, and solution ionic strength. For large pore sized Silica 1 membrane (1 mm), the maximum linear flow rate Qmax, was 3*10-6 m/s at 200V while the maximum pressure was 0.16 MPa, Decreasing the pore size to 50 nm allowed the same pressure to be achieved with only 5V. The efficiency of the EO pump was greater at lower salt concentrations; however, the maximum flow rate and pressure were also reduced under these conditions. The experimental data were in good agreement with model calculations for electroostmotic flow through an array of parallel cylindrical pores. High performance pumps were constructed by properly staging several inorganic membranes, significantly increasing the maximum pressure output while maintaining a low total voltage. The resulting electroosmotic pumps have potential applications in a variety of systems.

Key words: Electroosmotic pump, zeta potential, electrokinetics