Electrochemical membrane microactuator with a millisecond response time

Abstract

Lack of fast and strong actuators to drive microsystems is well recognized. Electrochemical actuators are considered attractive for many applications but they have long response time (minutes) due to slow gas termination. Here an electrochemical actuator is presented for which the response time can be as short as 1ms. The alternating polarity water electrolysis is used to drive the device. In this process only nanobubbles are formed. The gas in nanobubbles can be terminated fast due to surface assisted reaction between hydrogen and oxygen that happens at room temperature. The working chamber of the actuator contains concentric titanium electrodes; it has a diameter of 500 µm and a height of 8 µm. The chamber is sealed by a polydimethylsiloxane (PDMS) membrane of 30µm thick. The device is characterized by an interferometer and a fast camera. Cyclic operation at frequency up to 667 Hz with a stroke of about 30% of the chamber volume is demonstrated. The cycles repeat themselves with high precision providing the volume strokes in picoliter range. Controlled explosions in the chamber can push the membrane up to 90 µm.

Explosion of Microbubbles Generated by the Alternating Polarity Water Electrolysis

“…One of the promising applications is an actuation mechanism to drive microelectromechanical systems and specifically microfluidic systems. It was already demonstrated [26] that the explosion of a MB in a closed chamber covered with a flexible membrane gives the deflection of the membrane that is 20 times larger than the deflection produced in the same process without generation of the MBs. This is an attractive regime to drive micropumps.…”

“…In Refs. [26,35], formation and disappearance of such MBs were observed in closed volumes covered with a flexible membrane. After many cycles the membrane always returned to its initial position indicating complete termination of H 2 and O 2 gases in the chemical reaction.…”

“…It makes explosions more stable and more powerful; the sound produced by the explosions is more pronounced. These electrodes demonstrated the best durability for the AP process [26], which is especially important for microdevices using AP electrolysis. Several other materials such as Pt, Au, W, Cu, and Fe have been investigated as thin film electrodes.…”

“…The upper limit was restricted by electronics and for this reason it is not known if the process itself limits the highest frequency. The driving signal was provided by a homemade PC-controlled signal generator (for details, see [26]). The voltage and current flowing through the electrodes were recorded by a PicoScope 5000.…”

“…Spontaneous combustion of H 2 and O 2 gases in NBs was proposed to explain gas disappearance in the AP electrochemical process [9]. It was demonstrated that one can use this effect as a driving principle for a fast and strong microactuator [26] to drive microfluidic and other microdevices in autonomous regime. However, according to the classical theory combustion in small volumes has to quench due to fast heat escape [27,28].…”