An electroosmotic (EO) actuator offers a low-power, low-voltage alternative in a diaphragm-based periodic displacement micropump intended for an implantable drug delivery system. The actuator utilizes an electroosmosis mechanism to transport liquid across a membrane to deflect the pumping diaphragms in a reciprocating manner. In the study, the membrane made of porous nanocrystalline silicon (pnc-Si) tens of nanometers in thickness was used as the promising EO generator with low power consumption and small package size. This ultrathin membrane provides the opportunity for electrode integration such that the very high electric field can be generated across the membrane with the applied potential under 1 volt for low flow rate applications like drug delivery. Due to such a low applied voltage, the challenge, however, imposes on the capability of generating the pumping pressure high enough to deflect the pumping diaphragms and overcome the back pressure normally encountered in the biological tissue and organ.;This research identified the cause of weak pumping pressure that the electric field inside the orifice-like nanopores of the ultrathin membrane is weaker than conventional theory would predict. It no longer scales uniformly with the thickness of membrane, but with the pore length-to-diameter aspect ratio for each nanopore. To enhance the pumping performance, the pnc-Si membrane was coated with an ultrathin Nafion film. As a result, the induced concentration difference across the Nafion film generates the osmotic pressure against the back pressure allowing the EO actuator to maintain the target pumping flow rate under 1 volt.
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