A Novel On-Chip Liquid-Metal-Enabled Microvalve

Abstract

A room temperature liquid metal-based microvalve has been proposed in this work. The microvalve has the advantages of easy fabrication, high flexibility, and a low leak rate. By designing a posts array in the channel, the liquid metal can be controlled to form a deformable valve boss and block the flow path. Besides, through adjustment of the pressure applied to the liquid metal, the microvalve can perform reliable switching commands. To eliminate the problem that liquid metal is easily oxidized, which causes the microvalve to have poor repeatability, a method of electrochemical cathodic protection has been proposed, which significantly increases the number of open/close switch cycles up to 145. In addition, this microvalve overcomes the shortcomings of the traditional microvalve that requires an alignment process to assemble all the parts. When the valve is closed, no leak rate is detected at ≤320 mbar, and the leak rate is ≤0.043 μL/min at 330 mbar, which indicates it has good tightness. As an application, we also fabricate a chip that can control bubble flow based on this microvalve. Therefore, this microvalve has great prospects in the field of microfluidics.

Keywords: easy fabrication; high switching ratio; liquid metal microvalve; repeatability.

Figure 1

Structure diagrams of the microvalve. (a) Schematic of “T”-shaped microvalve; the vertical channel was filled with liquid metal, and lateral flow channel was filled with the sample fluid. (b) The plane structure of the microvalve with an inclination angle of 45°. (c) Photographs of the microvalve and its micro-structure under a microscope.

Figure 2

The control and flow detection platform of a microvalve and a valve switch diagram. (a) A computer works as a control module connected to a four-channel microfluidic control system (for pumping the liquid metal and Di water into the microchannels), and a flow rate platform (includes a FLOWBOARD and a FLOW UNIT model) to detect the flow rate of Di water. A high voltage sequencer is used to apply cathodic protection: the liquid metal inlet is connected to the cathode, and the anode is connected to the Di water outlet and grounded separately. (b) The close (i) and open (ii) state of the microvalve observed by a microscope.

Figure 3

Study on valve closing conditions and valve closing diagram. (a) Liquid metal pressure ranges required for valve closing with and without voltage applied. (b) Different types of microvalves in closed state: (i) 30° inclination angle, (ii) 45° inclination angle, (iii) 60° inclination angle, (iv) 75° inclination angle, (v) 90° inclination angle.

Figure 4

Diagram of the first three openings of the valve under different voltages: (a1) without cathodic protection; (b1–b3) opening status of the valve the first three instances at −100 V; (c1–c3) opening status of the valve in the first three instances at −400 V; (d1–d3) opening status of the valve in the first three instances at −800 V; (e1–e3) opening status of the valve in the first three instances at −1500 V.

Figure 5

Repeatability test of microvalves. (a) Cycle switching tests for the valve and amplification curve for last 5 cycles. (b) The comparion of the first 5 cycles and the last 5 cycles. (c) Maximum number of cycles for different valve angles.

Figure 6

Leakage and response time tests of microvalves. (a) A line graph of sample flow rate as a function of pressure when the valve was opened. (b) A line graph of sample flow rate as a function of pressure when the valve was closed. (c) Comparison of our microvalve and other microvalves reported in the current literature on leak rate. (d) A line graph of the open/closed flow ratios of the valves under different pressures. (e) The relationship curve between the flow rate and time for one complete switching process of a 30° valve. (f) Response times for all valves of different angles.

Figure 7

Morphological changes of microvalves at burst pressure and burst pressure values under different conditions. (a) The microvalves were completely closed. (b) Partial gaps appeared in the microvalves. (c) Burst pressure curve for the microvalves of different angles.

Figure 8

Bubbles’ flow direction manipulated by two microvalves in Y-shaped channel. (a) Before two valves were closed. (b) The lower side valve was closed. (c) Both the upper and lower side valve were closed. (d) The lower side valve was opened. (e) The upper side valve was opened. (f) Both the upper and lower side valve were opened.