A method for achieving micro-liquid self-driving by constructing a wetting gradient based on plasma technology

Abstract

This invention provides a method for constructing a wetting gradient based on plasma technology to achieve micro-liquid self-driving. Step S01: After preparing a hydrophobic thin film, the change curve of the water contact angle on the treated surface with respect to treatment time is obtained through curve fitting. Step S02: The surface water contact angle at each node of the motion trajectory curve is determined. Combined with the curve obtained in step S01, the corresponding treatment time for each node is determined. Step S03: Based on the motion trajectory in step S02, a mask track is constructed to define the self-driving trajectory of the liquid. Step S04: The movement of the atmospheric pressure jet device is controlled, ensuring that the movement path of the jet plume center is consistent with the center of the track constructed in step S03, and the dwell time at each node is consistent with the treatment time determined in step S02, thus achieving precise modification of each designed node. This invention enables spontaneous long-distance transport of microdroplets to a wetting gradient surface, and can be applied in the manufacture of condenser components, microfluidic devices, and anti-icing surfaces.

Description

Technical Field

[0001] This invention pertains to plasma-constructed wetting gradients and relates to a method for achieving micro-liquid self-driving by constructing a wetting gradient based on plasma technology. Background Technology

[0002] Surface wetting gradient (WGS) refers to a surface with a special morphology whose wetting properties vary across different surface regions, enabling self-driven liquid movement. In the field of micro / nano manufacturing, surface wetting gradient treatment can be applied to microfluidic systems and micromechanical devices. By designing surface wetting gradients or structural features, droplets can flow automatically within microchannels, avoiding the need for external pressure or pumping. The self-driven nature of microfluidics reduces system complexity, cost, and energy consumption, while improving the accuracy and reliability of fluid control, which is of great significance for the application of microfluidics technology.

[0003] Existing methods for constructing wetting gradients mainly focus on constructing micron-scale physical morphologies and surface modification using chemical reagents. Physical methods for preparing material surface wetting gradients are difficult to scale up industrially due to the high precision of the instruments required and the inherent difficulties in preparation. Chemical methods for preparing material surface wetting gradients are difficult to control in terms of reaction conditions. Most widely used chemical methods cause a series of irreversible damages to the materials, thus limiting their applicability. Furthermore, existing methods often fail to meet the long-distance self-driven requirements of small droplets (<5 μL). Summary of the Invention

[0004] 1. The technical problem to be solved:

[0005] Existing methods for preparing surface wetting gradients are difficult to implement on a large industrial scale. Reaction conditions are hard to control. Most widely used chemical methods cause irreversible damage to the material, thus limiting their applicability. Furthermore, existing methods often fail to meet the long-distance self-driven requirements of small droplets (<5 μL).

[0006] 2. Technical Solution:

[0007] To address the above problems, this invention provides a method for constructing a wetting gradient based on plasma technology to achieve micro-liquid self-driving, comprising preparing a hydrophobic film on a material substrate and modifying the wetting gradient on the hydrophobic film, the specific method being as follows:

[0008] Step S01: After preparing a hydrophobic film on the material substrate, static hydrophilic modification calibration is performed on the hydrophobic film to obtain the water contact angle corresponding to different treatment times. Then, the change curve of the water contact angle of the treated surface with respect to the treatment time is obtained by curve fitting.

[0009] Step S02: Based on the wetting gradient requirements at different positions on the self-driven liquid trajectory, determine the surface water contact angle of each node on the motion trajectory curve, and then combine it with the curve obtained in step S01 to determine the corresponding processing time for each node.

[0010] Step S03: Based on the motion trajectory in step S02, create a mask track to define the self-driving trajectory of the liquid.

[0011] Step S04: Control the movement of the atmospheric pressure jet device, the movement path of the jet plume center position is consistent with the track center made in step S03, and the dwell time of each node is consistent with the processing time determined in step S02, so as to achieve precise modification of each designed node.

[0012] The hydrophobic thin film is prepared on the substrate using a DBD (Deep Booster) apparatus. The apparatus includes a glass dish in which the substrate is placed. A glass plate covers the glass dish, sealing the interior. A high-voltage electrode is connected above the glass plate, and a ground electrode is connected below the glass dish. An upper support plate is connected above the high-voltage electrode, and a lower support plate is connected below the ground electrode. The upper and lower support plates are connected by multiple vertical support columns. A main gas path and an auxiliary gas path mixing unit are introduced into the glass dish via pipes passing through the upper support plate and the glass plate.

[0013] The high-voltage electrode is connected to a high-voltage pulse power supply unit, which is a nanosecond pulse power supply with the following parameters: voltage amplitude of 12kV, repetition frequency of 4-6kHz, rise time of 95-105ns, pulse width of 750-850ns, and fall time of 95-105ns.

[0014] In the main gas path and auxiliary gas path mixing gas path unit, the main gas path is filled with high-purity argon gas at a flow rate of 0.9-1.1 L / min, the auxiliary gas path is filled with a medium, and HMDSO is introduced into the mixing gas path by bubbling method at a flow rate of 13-15 mL / min and a discharge gas gap of 6-8 mm.

[0015] Before preparing a hydrophobic film on the substrate material surface, the substrate material is placed in an ultrasonic cleaner containing deionized water for 5 minutes, and then placed in an 80°C drying oven for 20 minutes.

[0016] In step S04, the movement of the atmospheric pressure jet device is controlled by a robotic arm. The robotic arm fixes the jet tube, and the upper end of the jet tube is connected to a high-voltage pulse power supply and a main gas path and auxiliary gas path mixing gas path unit. The distance between adjacent nodes is 1-2 times the diameter of the inner wall of the jet tube, and the movement speed of the robotic arm between nodes is set to 2-4 mm / s.

[0017] The jet tube is a quartz glass tube with an inner diameter of 1.5-2.5 mm and an outer diameter of 3-5 mm. The high-voltage electrode is 18-22 mm from the ground electrode, the ground electrode is 13-17 mm from the tube opening, and the tube opening is 20-30 mm from the treatment area. The nanosecond power supply parameters are: voltage amplitude 11 kV, repetition frequency 5 kHz, rise time 95-105 ns, pulse width 750-850 ns, and fall time 95-105 ns.

[0018] The robotic arm is a six-degree-of-freedom robotic arm, model xArm 6, manufactured by UFactory.

[0019] 3. Beneficial effects:

[0020] 1) This invention utilizes plasma to construct a wetting gradient surface, improving preparation efficiency and greatly simplifying the preparation process from both the physical morphology and chemical composition of the material surface, and the self-driven motion trajectory is precisely controllable.

[0021] 2) The method of the present invention has low production cost for preparing wetting gradient surfaces, does not require large and complex equipment such as lasers, requires little chemical reagents and is non-toxic, and can achieve liquid self-driving on the surface of any substrate material.

[0022] 3) The method of this invention utilizes mask-assisted plasma treatment, which not only standardizes the trajectory of the micro-liquid movement but also reduces the mass loss caused by the "viscous residue" at the hydrophilic contact surface during the movement of the micro-liquid. Compared with no mask, the mask significantly enhances the movement distance of the micro-liquid.

[0023] 4) The micro-liquid self-driving distance for preparing a wetting gradient surface according to the present invention is long, enabling a 2μL droplet to move horizontally for 27.4mm on the gradient surface. In this respect, the method of the present invention is significantly more effective than other methods. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an apparatus for preparing hydrophobic films on the surface of a substrate material using DBD.

[0025] Figure 2 This is the curve showing the change of WCA on the surface of the thin film substrate with the jet treatment time.

[0026] Figure 3 This is a schematic diagram of a jet device for preparing a wetting gradient.

[0027] Figure 4 The images are ICCD images of discharge at different HMDSO concentrations: (a) at low concentration; (b) at 13-15 mL concentration; and (c) at high concentration.

[0028] Figure 5 (a) is a schematic diagram of the chemical composition of a hydrophilically modified wetting gradient surface; Figure 5 (b) Schematic diagram of force analysis of liquid on wetting gradient surface.

[0029] Figure 6 (a) shows the motion of a 2 μL droplet on the surface of the wetting gradient in Scheme 1; Figure 6 (b) The motion of a 4 μL droplet on the surface of the wetting gradient in Scheme 2.

[0030] Explanation of reference numerals in the attached diagram: 1. High voltage electrode; 2. Ground electrode; 3. Glass plate; 4. Upper support plate; 5. Support column; 6. Lower support plate; 7. Base; 8. Glassware. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] A method for achieving microliquid self-driving by constructing a wetting gradient based on plasma technology includes preparing a hydrophobic film on a material substrate and modifying the hydrophobic film with a wetting gradient. The specific method is as follows:

[0033] Step S01: After preparing a hydrophobic film on the material substrate, static hydrophilic modification calibration is performed on the hydrophobic film to obtain the water contact angle corresponding to different treatment times. Then, curve fitting is used to obtain the change curve of the water contact angle of the treated surface with respect to treatment time, as shown below. Figure 2 As shown, by establishing the variation curve of the water contact angle of the treated surface in the treatment area with respect to treatment time, wetting gradients of WCA with arbitrary orbits, gradients, and positions can be prepared.

[0034] Step S02: Based on the wetting gradient requirements at different positions on the self-driven liquid trajectory, determine the surface water contact angle of each node on the motion trajectory curve, and then combine it with the curve obtained in step S01 to determine the corresponding processing time for each node.

[0035] Step S03: Based on the motion trajectory in step S02, create a mask track to define the self-driving trajectory of the liquid.

[0036] Step S04: Control the movement of the atmospheric pressure jet device, the movement path of the jet plume center position is consistent with the track center made in step S03, and the dwell time of each node is consistent with the processing time determined in step S02, so as to achieve precise modification of each designed node.

[0037] In one embodiment, the hydrophobic film is prepared on the material substrate in a DBD apparatus for preparing a hydrophobic film on the surface of the substrate material, such as... Figure 1As shown, the device includes a glass container 8, with a substrate 7 placed inside. A glass plate 3 covers the glass container 8, sealing its interior. A high-voltage electrode 1 is connected above the glass plate 3, and a ground electrode 2 is connected below the glass container 8. An upper support plate 4 is connected above the high-voltage electrode 1, and a lower support plate 6 is connected below the ground electrode 2. The upper and lower support plates 4 and 6 are connected by multiple vertical support columns 5. The main and auxiliary gas path mixing unit enters the glass container 8 through pipes passing through the upper support plate 4 and the glass plate 3.

[0038] Hydrophobic treatment using atmospheric pressure DBD and wetting modification using atmospheric pressure plasma jets can produce wetting modifications over a wide range from 0° to 150°. The process is simple, energy-saving, environmentally friendly, safe, and efficient.

[0039] The main gas path carries high-purity argon, while the auxiliary gas path carries a medium. HMDSO is introduced into the mixed gas path using a bubbling method.

[0040] When the concentration of the silicon-containing medium HMDSO is low, the discharge becomes more unstable, and filamentous discharges appear in the discharge space. When the HMDSO concentration is high, the discharge becomes more difficult, and the formation of discharge filaments is more challenging, resulting in a more uniform discharge. An appropriate amount of HMDSO can achieve a transitional state between these two states—a mixed discharge of uniformity and filaments. Experiments have shown that large-area and relatively uniform hydrophobic films can be prepared under this condition.

[0041] In one embodiment, the high-voltage pulse unit is a nanosecond pulse power supply with the following parameters: voltage amplitude 12kV, repetition frequency 5kHz, rise time 100ns, pulse width 800ns, and fall time 100ns. The main gas path carries high-purity argon at a flow rate of 1L / min. The auxiliary gas path carries a medium, using a bubbling method to introduce HMDSO into the mixed gas path at a flow rate of 14mL / min. The discharge gap is 7mm, forming a mixed-mode discharge with both filamentary and diffused plasma. Under the influence of the gas flow, the filament position continuously changes, allowing the deposited film to cover the entire area. The discharge processing time is 12min, resulting in a hydrophobic film with a large area.

[0042] The atmospheric pressure DBD method used in this invention employs a hybrid discharge mode, which can perform hydrophobic modification on any substrate and has versatility.

[0043] The method of this invention for preparing wetting gradient surfaces has low production costs, does not require large and complex equipment such as lasers, requires small amounts of non-toxic chemical reagents, and can achieve self-driven liquid flow on any substrate material surface.

[0044] The method of this invention utilizes mask-assisted plasma processing, which not only standardizes the trajectory of the microfluidic liquid but also reduces mass loss caused by "viscous residue" at the hydrophilic contact surface during movement. Compared with no mask, the mask significantly enhances the movement distance of the microfluidic liquid.

[0045] In one embodiment, in step S04, the movement of the atmospheric pressure jet device is controlled by a robotic arm, which is a six-degree-of-freedom robotic arm of model xArm 6 manufactured by UFactory.

[0046] like Figure 3 As shown, the robotic arm fixes the jet tube, with the bottom section of the jet tube 20-30mm away from the mask of the surface to be treated. The upper end of the jet tube is connected to a high-voltage pulse power supply and a main and auxiliary gas path mixing unit. The method of this invention indirectly controls the surface wetting degree of the material by controlling the processing time. Therefore, by processing different node positions for different times, a material surface with a wetting gradient can be prepared on a hydrophobic film. When designing the wetting gradient, to maintain the optimal processing range, the distance between adjacent nodes is kept at 1-2 times the diameter of the inner wall of the jet tube. Therefore, the distance between two adjacent nodes is 3mm in this case. Furthermore, the robotic arm's movement speed between nodes is set to 3mm / s.

[0047] By using a mask to restrict droplet movement and combining optimized parameters such as node distance, processing distance, and discharge parameters, the distance of micro-liquid movement can be significantly extended.

[0048] In one embodiment, the plasma jet tube is a quartz glass tube with an inner diameter of 2 mm and an outer diameter of 4 mm. The high-voltage electrode is 20 mm from the ground electrode, the ground electrode is 15 mm from the tube opening, and the tube opening is 28 mm from the treatment area. The nanosecond power supply parameters are: voltage amplitude 11 kV, repetition frequency 5 kHz, rise time 100 ns, pulse width 800 ns, and fall time 100 ns. Pure argon is used for hydrophilic treatment, and the gas flow rate is 1 L / min.

[0049] This invention relates to an atmospheric pressure DBD with a hybrid mode discharge exhibiting both filamentary and diffuse plasma. Figure 4 ICCD images showing the discharge characteristics at different HMDSO concentrations. The luminescence images obtained at 14 mL / min using the method of this invention are as follows... Figure 4 As shown in (b).

[0050] This invention relates to a method for constructing a wetting gradient based on plasma technology to achieve liquid self-propulsion. The method utilizes a low-temperature plasma jet at atmospheric pressure under an argon atmosphere to alter the microscopic morphology of the material surface and react with H2O, O2, etc., in the air to introduce hydrophilic groups such as COOH and OH on the material surface. Figure 5 As shown in (a). Both aspects contribute to improving the hydrophilicity of the treated area. By controlling the treatment time, the wetting degree of different areas can be effectively adjusted, thereby obtaining a surface with excellent wetting gradient performance. Figure 5 (b) shows the forces acting on the droplet on the wetting gradient surface. The main factors affecting the droplet's motion include resistance... f and driving force F l The driving force is mainly provided by the Laplace pressure difference inside the droplet caused by the gradient difference between the contact surfaces, which is specifically manifested in the advancing contact angle. θ a and backward contact angle θ b When F l > f At that time, the droplet can begin to move.

[0051] The method of this invention was tested with various wetting gradient design schemes, all of which achieved superior liquid self-driving performance. The following lists the WCA (Wetting Capacity Aspect Ratio) at each node in two different wetting gradient design schemes:

[0052] Option 1: 124° 109° 99° 82° 68° 53° 40° 27° 13° 0°

[0053] Option 2: 124° 109° 91° 75° 59° 45° 30° 13° 0°

[0054] The effective processing distance of the wetting gradient in Scheme 1 is about 30 mm, and the effective processing distance of the wetting gradient in Scheme 2 is about 27 mm. Figure 6 (a) Figure 6 (b) The horizontal motion of a 2 μL droplet on the wetting gradient surface of Scheme 1 and a 4 μL droplet on the wetting gradient surface of Scheme 2, respectively. The 2 μL droplet travels a distance of 27.4 mm and a speed of 35.9 mm / s on the wetting gradient surface of Scheme 1. The 4 μL droplet travels a distance of 24.6 mm and a speed of 75.9 mm / s on the wetting gradient surface of Scheme 2.

[0055] The two methods described above demonstrate that the micro-liquid self-driving distance for preparing a wetting gradient surface is long, enabling a 2 μL droplet to move horizontally for 27.4 mm across the gradient surface. In this respect, the method of this invention is significantly more effective than other methods.

Claims

1. A method for fabricating a wetting gradient based on plasma technology to realize self-driven microfluidics, comprising preparing a hydrophobic film on a material substrate, characterized in that: The wetting gradient modification is performed on the hydrophobic film, and the specific method is as follows: Step S01: After the hydrophobic film is prepared on the material substrate, static hydrophilic modification calibration is performed on the hydrophobic film, the water contact angle corresponding to different treatment times is obtained, and then the change curve of the water contact angle of the treated surface with respect to the treatment time is obtained through curve fitting; Step S02: According to the wetting gradient requirement of different positions on the liquid self-driving track, the surface water contact angle of each node of the motion track curve is determined, and then the treatment time corresponding to each node is determined in combination with the curve obtained in step S01; Step S03: According to the motion track of step S02, a mask track is made to limit the liquid self-driving track; Step S04: The atmospheric pressure jet device is controlled to move, the center position motion path of the jet body is consistent with the center of the track made in step S03, and the residence time of each node is consistent with the treatment time determined in step S02, so that accurate modification of each node designed is realized.

2. The method of claim 1, wherein the microfluid self-actuation is achieved by constructing a wetting gradient based on plasma technology. The hydrophobic film prepared on the material substrate is prepared in a DBD device for preparing a hydrophobic film on the surface of a substrate material, the device comprising a glassware (8), the substrate (7) being placed in the glassware (8), a glass plate (3) being arranged above the glassware (8) to cover the glassware (8), so that the glassware (8) is in a sealed state, a high-voltage electrode (1) being connected above the glass plate (3), a ground electrode (2) being connected below the glassware (8), an upper support plate (4) being connected above the high-voltage electrode (1), a lower support plate (6) being connected below the ground electrode (2), the upper support plate (4) and the lower support plate (6) being connected by a plurality of vertical support columns (5), and a main gas path and auxiliary gas path mixed gas path unit entering the glassware (8) through the upper support plate (4) and the glass plate (3) by a pipeline.

3. The method of claim 2, wherein the microfluid is self-driven by the wetting gradient formed by the plasma technology. The high-voltage electrode (1) is connected to a high-voltage pulse power supply unit, the high-voltage pulse unit is a nanosecond pulse power supply, and the power supply parameters are a voltage amplitude of 12 kV, a repetition frequency of 4-6 kHz, a rising edge of 95-105 ns, a pulse width of 750-850 ns, and a falling edge of 95-105 ns.

4. The method of claim 2, wherein the microfluid self-actuation is achieved by constructing a wetting gradient based on plasma technology. In the main gas path and auxiliary gas path mixed gas path unit, high-purity argon is passed through the main gas path at a flow rate of 0.9-1.1 L / min, and a medium is passed through the auxiliary gas path, and HMDSO is brought into the mixed gas path by a bubbling method, and the flow rate of the auxiliary gas path is 13-15 mL / min, and the discharge gap is 6-8 mm.

5. The method of claim 1-4, wherein the method is based on plasma technology to fabricate a wetting gradient to achieve self-driven microfluidic. Before the hydrophobic film is prepared on the surface of the substrate material, the substrate is placed in an ultrasonic cleaner filled with deionized water for cleaning for 5 min, and then placed in a drying oven at 80° for drying for 20 min.

6. The method of claim 1-4, wherein the microfluid self-propulsion is achieved by constructing a wetting gradient using plasma technology. In step S04, the atmospheric pressure jet device is controlled to move by using a mechanical arm, the mechanical arm fixes the jet pipe, the upper end of the jet pipe is connected to the high-voltage pulse power supply and the main gas path and auxiliary gas path mixed gas path unit, the distance between adjacent nodes is 1-2 times the diameter of the inner wall of the jet pipe, and the mechanical arm moving speed between nodes is set to 2-4 mm / s.

7. The method of claim 6, wherein the microfluid self-actuation is achieved by constructing a wetting gradient based on plasma technology. The jet pipe is a quartz glass pipe, the inner diameter is 1.5-2.5 mm, the outer diameter is 3-5 mm, the distance between the high-voltage electrode and the ground electrode is 18-22 mm, the distance between the ground electrode and the pipe opening is 13-17 mm, the distance between the pipe opening and the processing area is 20-30 mm, the nanosecond power supply parameters are a voltage amplitude of 11 kV, a repetition frequency of 5 kHz, a rising edge of 95-105 ns, a pulse width of 750-850 ns, and a falling edge of 95-105 ns.

8. The method of claim 6, wherein the microfluid self-actuation is achieved by constructing a wetting gradient based on plasma technology. The mechanical arm is a six-degree-of-freedom mechanical arm produced by UFactory Company and the model number is xArm 6.

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