Electroosmotic Pumps

We are developing high performance electroosmotic pumps for variety of applications including IC chip cooling, drug delivery, high performance liquid chromatography, and water management in hydrogen PEM fuel cells. Electroosmotic (EO) pumps use ion drag in micro- and nano-scale flow channels to pump electrolytes. EO flow is the motion of an electrolyte caused by the interaction of an external electric field with the diffuse charges of electrical double layers (EDLs) which form at electrolyte/surface interfaces. EO pumps are fabricated from porous structures which can be modeled as EO flow through many, sometimes torturous, channels in parallel. Yao and Santiago (J. Colloid and Interface Science, 2003) have developed and validated detailed models of the flow rate, current, and pressure of electroosmotic pumps in porous materials.

An EO pump is modeled as many cylindrical microchannels in parallel. An electric field is imposed using two electrodes on either side of the porous substrate. The flow is driven by the motion of net charge in the EDL that drags the bulk fluid by viscosity (a) image of EO pump with integrated gas recombination system (b) detailed view of flow in one pore adapted from Yao and Santiago JOCIS 2003. (c) SEM image of porous silicon based EO pump.
Pumps have been fabricated from glass-particle-packed fused silica capillaries, porous borosilicate glass, in situ polymerized porous monoliths, as well as planar and porous silicon. EO pumps can generate high pressures of more than 340 atm and large flow rates per volt and unit area 0.13 ml/min cm&#178 V. For example we can pump 40 ml min&#175&#185 of solution at 100 V in a pumping structure less than 1 cm&#179 in total volume. We have also demonstrated that we can pump a wide variety of aqueous solutions and polar organic solvents. Some of these solvents include methanol, acetone, and acetonitrile.

We have also shown that we can capture the electrolytic gases formed at the electrodes and recombine them to reform water using Teflon coated Pt
catalysts. These pumps can be used at
any orientations (relative to gravity) so that that they can be used in
portable medical devices as well as a cooling option for laptop
microprocessors.

Flow rate versus backpressure for porous silicon EO pumps with various thicknesses of polysilicon deposition and 0.25 &#956m thick SiO2 surface layer at an applied potential of 25 V.
This work has been conducted as a collaboration with Juan G. Santiago at Stanford University and Alan Myers at Intel Corporation.

Representative Publications:

1. S. YAO, A.M. MYERS, J.D. POSNER, K.A. ROSE, AND J.G. SANTIAGO. 2006. Electroosmotic Pumps Fabricated from Porous Silicon Membranes, Journal of Microelectromechanical
Systems, Journal of Microelectromechanical Systems, V15, No. 3

2. Kim, D., J.D. Posner, and J.G. Santiago. High Flow Rate per Power Pumping of Aqueous Solutions and Organic Solvents with Electroosmotic Pumps. in Electrochemical Society (ECS) Transactions, Annual Electrochemical Society Meeting 2005. October 16-21, Los Angeles, CA.