Background
With the development of the performance and miniaturization of electronic components, the requirement for heat dissipation is higher and higher. The reliability of microelectronic devices is very sensitive to temperature, and the temperature rise of electronic devices can greatly reduce their reliability. The reliability of the device is reduced by 5% when the temperature of the device is increased by 1 ℃ at the level of 70-80 ℃. The development of future intellectualization requires that the CPU speed is increased by 2-3 orders of magnitude, and the existing air cooling technology cannot meet the heat dissipation requirement, so that a new liquid cooling technology needs to be developed. With the development of microfluidic systems, micropumps have become a key technology in microfluidic control and microelectronic cooling systems.
In a microfluidic system, a micro-flow driving and controlling technology of liquid is always a more critical technical problem. Control of microfluidics refers to control of fluids in systems or devices with feature sizes smaller than 1mm, and a driving technology for precise control of microfluidics is an inevitable requirement for the development of microfluidic systems. Therefore, microfluidic systems require the integration of controllable micropumps for pumping small volumes of microfluid, and the research of micropumps has become an important marker in the development of microfluidic systems.
The micropumps are structurally divided into mechanical micropumps and non-mechanical micropumps according to the operating principle, and the main difference between the mechanical micropumps and the non-mechanical micropumps is the presence or absence of moving parts. At present, mechanical micropumps mainly comprise: piezoelectric micropumps, electromagnetic micropumps, electrostatic micropumps, shape memory alloy micropumps, thermally driven micropumps and the like. The mechanical micropump has a long development history and a mature theory, can drive almost any type of liquid, and has the defects of easy friction generation, unstable pumping speed, micro leakage, short service life, difficult integration with a chip and the like in the micropump because of containing a moving part, and the reliability of the pump is greatly reduced. The non-mechanical micropump is a new direction for the research of the micropump.
The electroosmotic micro pump is the most important non-mechanical micro pump at present, and has the advantages of easiness in processing and control, no need of moving parts, high repeatability and reliability and the like. And can be classified into a dc electroosmosis driven micro pump and an ac electroosmosis driven micro pump according to the type of applied voltage. The direct current electroosmosis driving micropump has the advantages of adjustable flow, wide range, no piston, no valve, no dynamic seal, low manufacturing cost, simple design and the like, and is an effective liquid driving mode. The disadvantages are that high voltage and high direct current voltage (up to thousands of volts) are needed for the direct current electroosmosis fluid driving technology, potential safety hazards exist, electrolysis reaction is easy to occur to generate bubbles, a large amount of heat is generated, and the flowing stability of microfluid is further influenced. Because the voltage is very large and has certain harmfulness, the application range of the direct current electroosmosis pump is limited to a certain extent. Compared with the traditional direct current driving method, the alternating current driving method has the advantages of low applied voltage (the amplitude of the input signal voltage is generally less than 4V), capability of well inhibiting electrolytic reaction, easiness in integration with other micro devices and the like, so that the alternating current electroosmosis driving technology has important application value.
The driving liquid is mainly divided into aqueous solution and non-aqueous solution, the aqueous solution is widely applied in the biological field, and the liquid with the most extensive driving requirements in other fields is the non-aqueous solution, such as methanol, ethanol and the like, and is widely applied to systems such as micro fuel cells, chips, integrated circuits, electric appliance heat dissipation and the like. Only studies on alternating current electroosmosis driving aqueous solutions are conducted internationally, and no driving nonaqueous solutions are reported. At present, the method for driving the non-aqueous solution at home and abroad mainly adopts an injection type electro-hydraulic power pump, such as an ion drag pump.
The main principle is that a direct current high voltage is applied to an anode electrode to generate electrochemical reaction on the surface of the anode. The anode metal electrode material generates cations under the action of high voltage or the liquid generates ions through electrochemical reaction, and the ions are then injected into the liquid. The cations injected into the liquid are driven under the action of the electric field. Due to the action of the viscous forces, the energy of the cations is transferred to the fluid, causing the fluid to flow. This method has the advantage of being driven by substantially all solutions, including organic solutions that do not contain a charge, and has the disadvantage of consuming anode material at higher voltages, causing the micropump made by this method to fail very quickly.
At present, in a microfluidic system, the injection type electro-hydraulic power pump is adopted to drive a non-aqueous solution, so that the defects of high voltage, short service life and the like are caused, and a non-mechanical micropump cannot be applied to the microfluidic system in a large scale.
Disclosure of Invention
Therefore, the embodiment of the invention provides an alternating current electroosmosis driven asymmetric ethanol micropump and a working method thereof, the adopted alternating current electroosmosis driven asymmetric micropump has the advantages of low voltage, long service life and the like, the ethanol can be driven for a long time, and the defects of high voltage, short service life and the like of a non-aqueous solution driven by an injection type electro-hydraulic power pump and the like are overcome, so that the problem that the non-mechanical micropump cannot be applied to a microfluidic system in a large scale is caused.
In order to achieve the above object, an embodiment of the present invention provides the following:
an alternating current electroosmosis driving ethanol asymmetric micropump comprises a first metal electrode, a second metal electrode and a microchannel, wherein the first metal electrode and the second metal electrode are arranged in a mirror image opposite mode, a large electrode is arranged on the first metal electrode in an equidistant array, a small electrode is arranged on the second metal electrode in an equidistant array, and the large electrode and the small electrode are sequentially arranged in the microchannel in a staggered array.
In a preferred embodiment of the present invention, the ratio of the widths of the large electrode and the small electrode is 10:1, the width of the small electrode is 10 to 30 μm, and the width of the large electrode is 100 to 300 μm.
In a preferred embodiment of the present invention, the distance between the large electrode and the small electrode is 10 to 30 μm, and the distance between an electrode pair consisting of one large electrode and one small electrode and an adjacent electrode pair is 30 to 300 μm.
In a preferred embodiment of the present invention, the first metal electrode, the second metal electrode, the large electrode, and the small electrode are made of the same material and are made of any one of gold, platinum, and copper.
An alternating current electroosmosis driving ethanol asymmetric micropump working method is characterized by comprising the following steps:
s100, processing the asymmetric micropump on silicon, glass or polymethyl methacrylate, and placing an array formed by a large electrode and a small electrode of the asymmetric micropump in a microchannel;
s200, injecting an ethanol solution added with trace potassium hydroxide electrolyte into the micro-channel, and adjusting the conductivity of the ethanol solution to be 5-110 uS/cm;
and S300, connecting the alternating current positive electrode and the alternating current negative electrode with the first metal electrode and the second metal electrode, applying an alternating current signal, and driving the ethanol solution to flow.
In a preferred embodiment of the present invention, in step S300, the alternating current voltage applied to the first metal electrode and the second metal electrode is 1 to 10V, and the alternating current frequency is 5 to-500 Hz.
The embodiment of the invention has the following advantages:
the invention adds a small amount of KOH electrolyte in the ethanol solution, can drive the ethanol solution under lower voltage, and replaces the high voltage method adopted at present, the high voltage method mainly comprises the steps of applying high voltage to enable the anode metal electrode material to generate cations, the cations enter the liquid, and the cations in the liquid drive the solution under the action of an electric field.
And the microelectrode is designed into an asymmetric width, and then alternating current is applied to reduce the applied voltage and reduce the power consumption of the micropump.
Detailed Description
The present invention is described in terms of particular embodiments, other advantages and features of the invention will become apparent to those skilled in the art from the following disclosure, and it is to be understood that the described embodiments are merely exemplary of the invention and that it is not intended to limit the invention to the particular embodiments disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1:
as shown in figure 1, the invention provides an alternating current electroosmosis driven asymmetric ethanol micropump, which comprises a first metal electrode 1 and a second metal electrode 2 which are arranged in a mirror image mode, and a microchannel 5, wherein the micropump adopts the lithography technology of a microfluidic chip system to attach the metal electrodes to the surfaces of materials such as silicon, glass or polymethyl methacrylate.
The first metal electrode 1 is provided with a large electrode 3 in an equidistant array, the second metal electrode 2 is provided with a small electrode 4 in an equidistant array, the large electrode 3 and the small electrode 4 are sequentially arranged in the microchannel 5 in a staggered array, and the large electrode 3 and the small electrode 4 are sequentially arranged in a crossed manner according to a finger fork shape;
the micro-channel 5 is processed on the surface of materials such as silicon, glass, Polydimethylsiloxane (PDMS) or polymethyl methacrylate and the like by micro-processing technology,
and (3) encapsulating the metal large electrode 3 and the metal small electrode 4 with the groove of the micro-channel 5, placing the metal electrode 3 and the metal electrode 4 in the micro-channel 5, and processing to obtain the asymmetric micro-pump.
The method for encapsulating the metal electrode and the micro-channel 5 can adopt an adhesive method or a plasma bonding method.
The ratio of the width of the large electrode 3 to the width of the small electrode 4 is 10:1, the width of the small electrode 4 is 10 to 30 μm, and the width of the large electrode 3 is 100 to 300 μm.
The interval between the large electrode 3 and the small electrode 4 is 10-30 mu m, and the distance between the electrode pair formed by one large electrode 3 and one small electrode 4 and the adjacent electrode pair is 30-300 mu m.
The first metal electrode 1, the second metal electrode 2, the large electrode 3, and the small electrode 4 are made of the same material, and are made of any one of gold, platinum, and copper.
The principle of the AC electroosmosis driving fluid is that when AC voltage is applied to an electrode, an electric double layer is formed on the surface of the electrode, and the electric double layer is capacitive; the liquid above the electrodes is resistive, like a resistor.
For the first 1/2 periods, on the two electrodes, the ions in the electric double layer will be subjected to an electric field force F in a direction away from the center of the circle, and the force is equal and opposite, so that the fluid on the surfaces of the electrodes will flow outwards;
in the last 1/2 periods, the direction of the electric field changes, but the sign of the electric double layer charges changes, so the force of the electric field and the force direction of the fluid are not changed.
So that the direction of coulomb force applied to the charge does not change in one period, and a stable fluid vortex is formed.
Since the resultant force on the system is 0, although electroosmotic flow is generated on the surface of the electrode, no directional flow of liquid is generated in the system.
In the symmetric electrode model, although fluid can flow, directional movement of the fluid cannot be formed, and in order to make the fluid flow in one direction, the balance must be broken, and a feasible method is to use an asymmetric electrode.
When the large electrode 3 and the small electrode 4 are respectively connected with the positive electrode and the negative electrode of alternating current, after an alternating current signal is applied, the potential on the small electrode is set to be positive at a certain moment, and the potential on the large electrode 3 is set to be negative at a certain moment, excessive negative ions appear in the electric double layer near the small electrode 4, and excessive positive ions appear in the electric double layer near the large electrode 3.
Because the electric field intensity direction at this moment is from small electrode 4 to point to large electrode 3, there is horizontal component to the right, therefore, the fluid near small electrode 4 will move to the left because of the drive of anion in the electric double layer, and the fluid near large electrode 3 will move to the right because of the drive of positive ion in the electric double layer, because the electrode size is unequal, cause the net flowing direction of the fluid to be from left to right finally, namely point to large electrode 3 from small electrode 4;
when the direction of the electric potential on the electrode is switched at the next moment, the small electrode 4 is positively charged, the large electrode 3 is negatively charged, positive ions are present in the electric double layer near the small electrode 4, and the large electrode 3 is negative ions, because the direction of the electric field intensity is from the large electrode 3 to the small electrode 4 at this moment, the horizontal component is leftward, therefore, the fluid near the small electrode 4 still moves leftward and the fluid near the large electrode 3 moves rightward, and finally, the net flow direction of the fluid still moves from left to right.
Therefore, after the application of the alternating potential, although the potential applied to the electrodes at different times will change sign, a directed flow will be generated in the electrolyte solution, so that pumping and transport of the fluid can be achieved.
Example 2:
an alternating current electroosmosis driving ethanol asymmetric micropump working method comprises the following steps:
s100, processing the asymmetric micropump on silicon, glass or polymethyl methacrylate, and placing an array formed by a large electrode and a small electrode of the asymmetric micropump in a microchannel;
attaching a layer of metal microelectrode array on the surface of materials such as silicon, glass or polymethyl methacrylate by the lithography technology of a microfluidic chip system;
processing a micro-channel on the surface of materials such as silicon, glass, Polydimethylsiloxane (PDMS) or polymethyl methacrylate, packaging a metal microelectrode array and a micro-channel groove, and processing to obtain the asymmetric micropump;
the metal microelectrode array formed by the large electrode and the small electrode of the asymmetric micropump is arranged in the microchannel;
the large electrode and the small electrode can be externally applied with an alternating signal through the first metal electrode and the second metal electrode, respectively.
The packaging method of the metal microelectrode array and the micro-channel can adopt an adhesive method and can also adopt a plasma bonding method;
s200, injecting an ethanol solution added with a trace amount of potassium hydroxide electrolyte into the microchannel, or adding a trace amount of potassium hydroxide electrolyte into other alcohol solutions such as propanol and butanol, and driving by adopting the same method. Adjusting the conductivity of the ethanol solution to 5-110 uS/cm;
s300, connecting the positive electrode and the negative electrode of alternating current with the first metal electrode and the second metal electrode, applying an alternating current signal, and driving an ethanol solution to flow;
connecting positive and negative electrodes of sine wave alternating current with the first metal electrode and the second metal electrode, wherein the electrodes are randomly connected with the positive and negative electrodes of the alternating current signal, and applying the alternating current signal to the large and small electrodes by adjusting the voltage and frequency of the alternating current signal to drive the ethanol solution to flow.
In step S300, the alternating current voltage applied to the first metal electrode and the second metal electrode is 1-10V, and the alternating current frequency is 5-500 Hz.
The experimental result of driving ethanol by the asymmetric electroosmosis micropump is shown in figure 2, and the alternating voltage is 5V; measuring the position: at 9.1 μm above the electrode; 25 ℃, KOH solution, conductivity: 20.02. mu.s/cm, the spacing between the electrode pairs being: 100 μm, overall trend: when the frequency is lower than 50hz, the higher the frequency is, the faster the speed is, and after the frequency is higher than 50hz, the higher the frequency is, the slower the speed is; when the solution conductivity is 20.2 mus/cm and the alternating current frequency is 50hz, the speed of the electroosmotic driving fluid is maximum.
The micro-electrode damage phenomenon is not found in experiments, the micro-pump can be used for long-term experiments, the applied alternating voltage is only 5V, and the ion drag pump generally needs direct current voltage of more than 10V.
Micropumps are used mainly by integration in microsystems.
Although the invention has been described in detail above with reference to a general description and specific examples, it will be apparent to one skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.