Electro-osmotic actuation for micropump applications

An electro-osmotic actuation mechanism is explored for micropump applications where self contained, low power, miniaturized pumps are necessary. The principle of electro-osmosis through a cation selective membrane is used to develop a differential pressure which is used to deflect a pump membrane. In an electro-osmotic cell, there are electrolyte filled chambers on either side of an ion specific membrane. Hydrated cations migrate in an applied electric field, effectively pulling water molecules to the cathodic chamber. In such a setup, the polarity of the current can be periodically reversed causing the chambers to alternately fill and discharge. Since the chemical reactions are reversible, an operating window can be defined so that the electrodes do not degrade and gas bubbles do not form. Using data from the characterization of an ion specific membrane such as Nafion, design parameters were developed that could be used to build and operate a micropump using standard MEMS based fabrication and packaging technology. The design is compatible with a silicon substrate which could contain fluidic channels and chambers. Upper layers could be fabricated using laser cut plastic, Nafion membranes and elastomeric membranes. Characterization of the materials was done with an acrylic test cell that could be disassembled and reused [1]. Recommendations for the miniaturization and integration of the micropump were developed. Measurements of Nafion water transport properties were used to determine operating current requirements. Recommendations for the minimization of energy consumption is provided as related to chamber geometry. Possible explanations for anomalous effects observed during experimentation were explored through simulation