A fast electrochemical actuator in the non-explosive regime

Abstract

Microfluidic systems require a compact, energy-efficient and microtechnology-compatible actuator that pushes the liquid through the channels. Electrochemical devices are promising candidates, but they suffer from a long response time due to slow gas recombination. An actuator with a millisecond response time was demonstrated recently. A micron-sized chamber of the device with two titanium electrodes is sealed by a polydimethylsiloxane membrane. A series of microsecond voltage pulses of alternating polarity is applied to the electrodes. Nanobubbles generated in the chamber push the membrane up, but disappear quickly due to spontaneous combustion of hydrogen and oxygen. In this work, operation of the device is investigated in detail. The pulses with a frequency from 100 to 500 kHz are used for actuation. It is demonstrated that higher frequency and higher amplitude of the pulses provide larger deflection of the membrane, but finally the deflection is saturated. The stroke of 8–9 µm can be achieved. In a cyclic operation regime the actuator is driven by series of pulses. If the time interval between the series is too short, the gas accumulates in the chamber. The membrane lifts during several cycles and then oscillates in the lifted position. In this regime the operating frequency as high as several hundred hertz can be achieved. The higher the frequency, the higher is the lift. The stroke also increases with the frequency, making a higher value more beneficial. Destruction of the electrodes is not observed, but the oxidation of titanium with time suppresses the gas production and decreases the membrane deflection. At a high frequency of the pulses the oxidation goes slower, but still significantly affects the performance. The oxidation of the electrodes is recognized as the main problem of the device. Methods to solve the problem are proposed.