Liquid metal-based tilt angle sensor with wettability regulated and controlled by graphite, preparation method and application

Abstract

The invention relates to a liquid metal tilt angle sensor with wettability regulated and controlled by graphite, which comprises a flexible polymer matrix, a liquid metal layer and a graphite layer, the graphite coating covers part of the surface of the inner wall of the micro-channel and is used for regulating and controlling the wettability of the inner wall; and the liquid metal is filled in the micro-channel and forms an axially continuous gradient section fluid. According to the method, the wettability of the inner wall to the liquid metal is regulated and controlled by coating the inner wall of the smooth flexible polymer micro-channel with graphite (and regulating the proportion of the coating area) by utilizing the characteristic that a graphite material is not wetted to the liquid metal. And by utilizing the surface oxidation film characteristic and high fluidity of the liquid metal, a liquid metal gradient section with instability can be formed in the pipeline. When the pipeline is inclined, the state (such as contact area or form) of the liquid metal surface can be changed under the action of gravity, so that the resistance of the liquid metal surface is influenced, and accurate angle detection can be realized.

Description

Technical Field

[0001] This invention belongs to the field of sensors, and particularly relates to a graphite-controlled wettability liquid metal-based tilt sensor, its preparation method, and its application. Background Technology

[0002] In recent years, the rapid development of industrial automation and intelligence has driven the growth in demand for tilt sensors. While traditional technologies (such as capacitive, inductive, and optical tilt sensors) offer high accuracy, their stringent environmental adaptability requirements and high manufacturing costs limit their suitability for many applications requiring high reliability and low cost. Liquid-based tilt sensors offer a more economical solution, but their insufficient stability and accuracy constitute a technological bottleneck, limiting their application potential in high-precision fields such as aerospace and precision manufacturing.

[0003] To address these issues, researchers are exploring new materials and mechanisms to overcome limitations and improve performance. Among these, gallium-based liquid metals, due to their excellent physicochemical properties such as non-toxicity, low volatility, and high conductivity, have become a key research focus, providing new insights for developing novel tilt sensing technologies. However, existing liquid metal sensors primarily rely on the macroscopic flow of the liquid medium, leading to insufficient accuracy and stability. Therefore, the application of liquid tilt sensors in aerospace, precision machinery manufacturing, and high-precision robotics remains limited by factors such as response speed and industrial production constraints.

[0004] To address the aforementioned challenges, this invention utilizes the inherent non-wetting property of graphite to liquid metal. The wettability of the inner wall of a smooth, flexible polymer microchannel to liquid metal is controlled by coating the inner wall with graphite (and adjusting the coating area ratio). This method cleverly leverages the surface oxide film characteristics and high fluidity of liquid metal to create an unstable liquid metal gradient section within the channel. When the channel is tilted, gravity alters the surface state of the liquid metal (such as contact area or morphology), thus affecting its resistance. The relationship between resistance and tilt angle can be used to achieve precise angle detection. This liquid metal-based sensing technology fully exploits the unique intrinsic properties of the material, simplifies sensor structure design, and effectively reduces costs. This design is expected to overcome the current bottlenecks in tilt sensors used in industrial applications, providing new opportunities for the development of related fields. Summary of the Invention

[0005] A first aspect of the present invention provides a graphite-controlled wettability liquid metal tilt sensor, comprising:

[0006] Flexible polymer matrix with internal microchannels;

[0007] Liquid metal is filled within microchannels to form an axially continuous gradient fluid.

[0008] And a graphite coating, covering part of the surface of the inner wall of the microchannel, for regulating the wettability of the inner wall.

[0009] The resistance value of the fluid in the gradient section changes with the tilt angle of the liquid metal tilt sensor.

[0010] Furthermore, the liquid metal tilt sensor also includes conductive electrodes, which are encapsulated at both ends of the microchannel using silver paste.

[0011] Furthermore, the graphite coating covers 30% to 70% of the surface area of ​​the inner wall of the microchannel.

[0012] In one embodiment of the present invention, the graphite coating covers 50% of the surface area of ​​the inner wall of the microchannel.

[0013] The microchannel can be a straight tube, a serpentine or spiral capillary tube with an inner diameter of 0.1 to 2 mm.

[0014] Furthermore, the microchannel is straight-tube shaped, and its cross-section is elliptical.

[0015] Furthermore, the liquid metal comprises one or more of gallium metal, gallium indium tin alloy, or gallium indium alloy, and its surface has an oxide film of 3-5 mm.

[0016] Furthermore, the gradient section fluid forms an axially non-uniform distribution through the dynamic balance between the surface tension of the liquid metal and gravity.

[0017] Furthermore, the flexible polymer material is selected from one or more of PDMS, TPU, PVP, or PVA.

[0018] A second aspect of the present invention provides a method for fabricating the liquid metal tilt sensor described in the first aspect, comprising the following steps:

[0019] (1) Preparation of substrate mixture: Mix flexible polymer material with curing agent, remove air bubbles by vacuuming to obtain mixture.

[0020] Furthermore, the flexible polymer material and the curing agent are mixed at a mass ratio of 2:1 to 20:1.

[0021] Furthermore, the curing agent is a prepolymer with vinyl side chains and a crosslinking agent.

[0022] (2) Forming microchannels: The microchannel mother plate is inserted into the mixture, vacuumed a second time, solidified and formed, and the mother plate is pulled out axially to form a flexible polymer matrix with microchannels.

[0023] Furthermore, the curing conditions are 70–100°C for 1–3 hours.

[0024] Furthermore, the microchannel mother plate has a straight tube shape, a serpentine shape, or a spiral shape.

[0025] In one embodiment of the present invention, the microchannel mother plate is a straight tubular steel needle.

[0026] (3) Coating functional layer: Graphite is coated on the inner wall of the microchannel, and the wettability of the inner wall is controlled by controlling the coating area ratio.

[0027] Furthermore, the graphite coating area ratio is 30% to 70% (that is, the graphite coating covers 30% to 70% of the surface area of ​​the inner wall of the microchannel).

[0028] In one embodiment of the present invention, the coating area of ​​graphite is 50%.

[0029] Furthermore, partial coating of graphite can be achieved by using mask spraying or local deposition.

[0030] (4) Injecting liquid metal: Injecting liquid metal into the microchannel to form an axially continuous gradient fluid.

[0031] Furthermore, the injection rate is 0.5–5 mL / min.

[0032] Furthermore, the liquid metal is injected at a non-uniform rate, which promotes the formation of gradient segments.

[0033] The non-uniform injection includes:

[0034] First stage: Continuously inject at 0.5-1 mL / min until the liquid metal fills the bottom 1 / 3 area (volume) of the microchannel;

[0035] Second stage: Inject continuously at 2-5 mL / min until the liquid metal completely fills the entire microchannel.

[0036] This invention actively creates instability in the flow of liquid metal by injecting it in stages and at non-uniform speeds. By utilizing the dynamic characteristics of the liquid metal oxide film, a controllable necking phenomenon is induced on surfaces with different wetting properties, promoting the formation of gradient segments and ultimately forming a gravity-sensitive gradient resistance structure, thereby further improving detection accuracy.

[0037] (5) Encapsulated electrodes: Conductive electrodes are encapsulated at both ends of the microchannel using silver paste.

[0038] A third aspect of the present invention provides a liquid metal tilt sensor as described in the first aspect or a liquid metal tilt sensor obtained by the preparation method described in the second aspect, for angle detection.

[0039] The beneficial effects of this invention are:

[0040] The tilt sensor design proposed in this invention utilizes the non-wetting property of graphite on liquid metal. By coating the inner wall of a smooth, flexible polymer material (such as silicone) with graphite and adjusting the percentage of the coating area, the wettability of the inner wall is precisely controlled. After injecting liquid metal into the microchannel capillary, the surface oxide film characteristics and high fluidity of the liquid metal are cleverly combined to form an unstable gradient section within the channel. When the channel is tilted, gravity affects the resistance of the liquid metal surface by changing its contact morphology. This resistance-tilt angle relationship can be used for high-precision angle detection.

[0041] The graphite-coated areas exhibit non-wetting properties to the liquid metal; the uncoated areas exhibit wettability due to hydrogen bonding between the oxide layer and the flexible polymer (such as silicone); at the wettability interface, the local curvature of the liquid metal is regulated by the additional pressure of gravity; based on the wettability established within the microchannel, the injection of liquid metal ultimately achieves a high-precision, high-sensitivity tilt sensing function.

[0042] This invention achieves ultra-high precision tilt sensing down to 1° (or lower) by partially coating the microchannel with a graphite layer and controlling the wettability of the graphite coating, breaking through the accuracy limits of existing technologies. This liquid metal sensing technology fully utilizes the unique intrinsic properties of the material, simplifying sensor structure design and significantly reducing costs. This design is expected to overcome the bottlenecks currently faced by tilt sensors in industrial applications, providing new opportunities for the development of related fields. This invention not only enriches the technical pathways for tilt sensing but also highlights the broad prospects of novel materials in sensor applications. This invention innovates and integrates theoretical foundations, material selection, and structural design, and is expected to be widely applied in complex applications with high requirements for cost and accuracy. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the fabrication process of the liquid metal tilt sensor of the present invention.

[0045] Figure 2 The tilt angle signal of the liquid metal tilt sensor prepared in Example 1 during the tilt detection process.

[0046] Figure 3 The tilt angle signal of the liquid metal tilt sensor prepared in Example 2 during the tilt detection process.

[0047] Figure 4 The tilt angle signal of the liquid metal tilt sensor prepared in Example 4 during the tilt detection process. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0049] Example 1

[0050] A method for fabricating a graphite-controlled wettability liquid metal tilt sensor includes the following steps (e.g.) Figure 1 As shown):

[0051] (1) Preparation of substrate mixture: Mix polydimethylsiloxane (PDMS) and curing agent at a mass ratio of 2:1, and remove air bubbles by vacuuming;

[0052] (2) Forming microchannels: Insert straight tubular steel needles into the mixture, vacuum the mixture twice, and cure it at 80°C for 3 hours to form a PDMS matrix. Pull out the steel needles axially to form straight tubular microchannels.

[0053] (3) Applying a graphite functional layer: Graphite is applied to the inner wall of the microchannel, and the coating area of ​​the graphite coating is controlled to account for 50% of the inner wall area of ​​the microchannel to regulate the wettability of the inner wall.

[0054] (4) Injecting liquid metal: Inject gallium indium tin alloy liquid metal into the microchannel (all) at a constant speed of 2 mL / min to form an axially continuous gradient fluid.

[0055] (5) Encapsulated electrodes: Conductive electrodes are encapsulated at both ends of the microchannel using silver paste.

[0056] Example 2

[0057] A method for fabricating a graphite-controlled wettability liquid metal tilt sensor is the same as the method in Example 1, except that:

[0058] Step (3) The area covered by the graphite coating is 70%.

[0059] Example 3

[0060] A method for fabricating a graphite-controlled wettability liquid metal tilt sensor is the same as the method in Example 1, except that:

[0061] Step (1) Mix polydimethylsiloxane (PDMS) and curing agent at a mass ratio of 10:1.

[0062] Example 4

[0063] A method for fabricating a graphite-controlled wettability liquid metal tilt sensor is the same as the method in Example 1, except that:

[0064] In step (4), the liquid metal is injected in a non-uniform and phased manner: first, it is continuously injected at 0.5 mL / min until the liquid metal fills 1 / 3 of the bottom area of ​​the entire microchannel; then the injection speed is increased to 2 mL / min and continued until the liquid metal completely fills the microchannel.

[0065] Example 5

[0066] A method for fabricating a graphite-controlled wettability liquid metal tilt sensor is the same as the method in Example 2, except that:

[0067] In step (4), the liquid metal is injected in a non-uniform and phased manner: first, it is continuously injected at 1 mL / min until the liquid metal fills 1 / 3 of the bottom area of ​​the entire microchannel, and then the injection speed is increased to 2 mL / min and continued until the liquid metal completely fills the microchannel.

[0068] Comparative Example 1

[0069] A method for preparing a liquid metal tilt sensor is the same as that in Example 1, except that: in step (3), the area of ​​the graphite coating accounts for 100%, that is, the entire microchannel is coated with graphite coating.

[0070] Performance testing:

[0071] The liquid metal tilt sensors obtained in the examples and comparative examples were connected to a turntable and an Agilent 34420A, respectively. The tilt angle signal can be obtained during the tilting of the sample, and the electrical performance is systematically evaluated. The results are shown in Table 1.

[0072] The detection performance of the tilt sensor with graphite-controlled wettability prepared in Example 1 is shown in [the figure]. Figure 2 The overall electrical signal change rate of this tilt sensor can reach 8.2% ( Figure 2 a) The monitoring range is -90 to 90° ( Figure 2 b) The optimal monitoring resolution can reach 1° ( Figure 2 c) The stability of cyclic operation can reach more than 2000 cycles. Figure 2 d), with a service life of up to 30 days. Figure 2 e), and has a core volume of less than 10 cubic millimeters and a response time of 0.24 s (e). Figure 2 c).

[0073] The detection performance of the tilt sensor with graphite-controlled wettability prepared in Example 2 is shown in [the figure]. Figure 3 The overall electrical signal change rate can reach 14% ( Figure 3 a) The monitoring range is -90 to 90° ( Figure 3 b) The optimal monitoring resolution can reach 1° ( Figure 3 c) The stability of cyclic operation can reach more than 2000 cycles. Figure 3 d), with a service life of up to 30 days. Figure 3 e), and has a core volume of less than 10 cubic millimeters and a response time of 0.36 s (e). Figure 3 c).

[0074] The detection performance of the tilt sensor with graphite-controlled wettability prepared in Example 4 is shown in [the figure]. Figure 4 The overall electrical signal change rate of this tilt sensor can reach 8.9% ( Figure 4 a) The monitoring range is -90 to 90° ( Figure 4 b) The optimal monitoring resolution can be as low as below 1°. Figure 4 c) The stability of cyclic operation can reach more than 2000 cycles. Figure 4 d), with a service life of up to 30 days. Figure 4 e), and has a core volume of less than 10 cubic millimeters and a response time of 0.24 s (e). Figure 4 c). Overall, under the same test conditions (e.g. Figure 4 As shown in Figure c, using a method of cyclically tilting to a preset angle and holding it for a certain period of time, the tilt sensor prepared in Example 4 not only maintains a large rate of change of electrical signal, but also significantly outperforms the other examples in terms of stability. Specifically, the electrical signal of Example 4 quickly reaches a steady state after a brief response and almost stops drifting; while other examples, although also having an initial response, continue to drift during the holding phase until the next angle change, at which point they recover. Therefore, Example 4 demonstrates significant advantages in both rapid response and long-term stable output.

[0075] This is because Example 4 actively creates instability in the liquid metal flow by injecting liquid metal at a non-uniform rate and in stages. Utilizing the dynamic characteristics of the liquid metal oxide film, it induces controllable necking on surfaces with different wetting rates, promoting the formation of gradient segments and ultimately creating a gravity-sensitive gradient resistance structure. This improves the monitoring accuracy of the tilt sensor (less than 1°) and reduces the response time. For the same reason, the tilt sensor in Example 5 also has a monitoring accuracy of <1°.

[0076] The tilt sensor prepared in Comparative Example 1 (using a full-coating process) exhibited a significant performance degradation: its electrical signal change rate decreased (6.6%), and both the monitoring range (-20 to 84°) and monitoring accuracy (greater than 5°) showed a significant decrease, while the response time increased significantly (1.2 s). This is because the liquid metal layer of the fully coated graphite lacks a gradient resistance structure, resulting in insufficient sensitivity of its resistance changes to the direction of gravity.

[0077] Table 1. LMT detection results of the samples prepared in the examples and comparative examples.

[0078]

[0079]

[0080] In summary, this invention innovates and integrates theoretical foundations, material selection, and structural design, and is expected to be widely applied in complex situations where cost and precision are critical.

[0081] The above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and are not intended to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the scope of the technology disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A graphite-controlled liquid metal tilt sensor, characterized in that, include: Flexible polymer matrix with internal microchannels; Liquid metal is filled within microchannels, forming an axially continuous gradient fluid segment. And a graphite coating, covering part of the surface of the inner wall of the microchannel, for regulating the wettability of the inner wall.

2. The liquid metal tilt sensor according to claim 1, characterized in that, The liquid metal tilt sensor also includes conductive electrodes, which are encapsulated at both ends of the microchannel using silver paste.

3. The liquid metal tilt sensor according to claim 1, characterized in that, The graphite coating covers 30% to 70% of the surface area of ​​the inner wall of the microchannel.

4. The liquid metal tilt sensor according to claim 1, characterized in that, The liquid metal comprises gallium metal, gallium indium tin alloy, or gallium indium alloy, and its surface has an oxide film; The flexible polymer material is selected from one or more of PDMS, TPU, PVP or PVA.

5. The method for preparing the liquid metal tilt sensor according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of substrate mixture: Mix flexible polymer material with curing agent, remove air bubbles by vacuuming to obtain mixture; (2) Forming microchannels: The microchannel mother plate is inserted into the mixture, vacuumed a second time, solidified and formed, and the mother plate is pulled out axially to form a flexible polymer matrix with microchannels. (3) Coating functional layer: Graphite is coated on the inner wall of the microchannel, and the wettability of the inner wall is controlled by controlling the coating area ratio. (4) Injecting liquid metal: Injecting liquid metal into the microchannel to form an axially continuous gradient fluid segment; (5) Encapsulated electrodes: Conductive electrodes are encapsulated at both ends of the microchannel using silver paste.

6. The preparation method according to claim 5, characterized in that, The flexible polymer material and curing agent described in step (1) are mixed at a mass ratio of 2:1 to 20:1; The curing conditions described in step (2) are: curing at 70–100°C for 1–3 hours; The microchannel mother plate described in step (2) has a straight tube, a serpentine shape, or a spiral shape; Preferably, the mother plate is a straight tubular steel needle.

7. The preparation method according to claim 5, characterized in that, In step (3), the graphite coating area ratio is 30% to 70%; the coating is carried out by mask spraying or local deposition.

8. The preparation method according to claim 5, characterized in that, In step (4), the injection rate of liquid metal is 0.5 to 5 mL / min.

9. The preparation method according to claim 8, characterized in that, The liquid metal is injected at a non-uniform rate: First stage: Inject continuously at 0.5-1 mL / min until the liquid metal fills the bottom 1 / 3 of the microchannel area; Second stage: Inject continuously at 2-5 mL / min until the liquid metal completely fills the microchannel.

10. The application of the liquid metal sensor according to any one of claims 1-4 or the liquid metal tilt sensor obtained by the preparation method according to any one of claims 5-9 in angle detection.

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