Method for preparing gallium-based liquid metal patterned circuit on rough flexible substrate through hydroxyl-rich gel coating

Abstract

The invention discloses a method for preparing a gallium-based liquid metal patterned circuit on a rough flexible substrate through a gel coating rich in hydroxyl, and belongs to the technical field of flexible electronic manufacturing. According to the method, a smooth hydrophilic interface is constructed on the surface of the rough flexible substrate by utilizing the gel solution rich in hydroxyl, so that the problem that gallium-based liquid metal cannot be directly moistened and spread on the rough surface is successfully solved, and the selection range of a liquid circuit substrate is widened. The area of the gel coating is predefined through the silk-screen printing patterning technology, and high-selectivity forming of the liquid metal circuit is achieved. Hydroxyl of the gel coating is combined with gallium oxide on the surface of the liquid metal through a strong hydrogen bond, so that the circuit and the substrate have excellent adhesive force, and the integrity and conductivity of the circuit can still be kept under bending and stretching conditions.

Description

Technical Field

[0001] This invention belongs to the field of flexible electronics manufacturing technology, and in particular relates to a method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate through a hydroxyl-rich gel coating. Background Technology

[0002] In the fields of soft electronics and wearable devices, achieving flexibility and stretchability in circuits is an important research direction. Gallium-based liquid metals, due to their unique low toxicity, high conductivity, and ability to remain liquid at room temperature, are ideal materials for soft electronics. However, the high surface tension of liquid metals makes it difficult to spread and form uniform thin films on solid surfaces, which limits their application in microelectronics and flexible electronic devices. Furthermore, gallium-based liquid metals are readily oxidized in air, forming a thin layer of gallium oxide (Ga2O3) film. This oxide film not only protects the internal metal from further oxidation but also, due to its chemical properties, becomes a key factor influencing the interaction between the liquid metal and the substrate.

[0003] Studies have shown that strong hydrogen bonding occurs between a substrate rich in hydroxyl groups (-OH) and an oxide film of gallium-based liquid metal, enabling the oxide film to adhere and spread on the substrate. This, in turn, promotes the wetting and spreading of the gallium-based liquid metal, ultimately achieving the printing of patterned circuits.

[0004] However, due to the high surface tension of gallium-based liquid metals and the properties of their oxide films, gallium-based liquid metals are difficult to wet on rough surfaces and can only be wetted and spread on smooth substrates (such as polyimide and smooth PDMS). This greatly limits their application on more diverse, low-cost flexible substrates (such as paper and porous membranes). Therefore, developing a method that can bridge rough substrates and liquid metals and achieve high-precision patterning is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating. This method utilizes a hydroxyl-rich hydrophilic gel solution to form a smooth transition layer on the surface of the rough substrate. Through hydrogen bonding between the hydroxyl groups and the liquid metal oxide film, high-precision patterning of the liquid metal is achieved on a traditionally non-wetting substrate.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate using a hydroxyl-rich gel coating includes the following steps: first, a patterned template is applied to the rough flexible substrate, and then a hydroxyl-rich gel solution is coated to form a patterned gel coating; gallium-based liquid metal is coated onto the patterned gel coating, the gallium-based liquid metal outside the patterned gel coating is removed, and after curing, a gallium-based liquid metal patterned circuit is formed.

[0007] Furthermore, the gelling substance in the hydroxyl-rich gel solution is selected from one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, and sodium alginate.

[0008] Furthermore, the concentration of the hydroxyl-rich gel solution is 8-20 wt.%.

[0009] Furthermore, the rough flexible substrate is selected from porous polyvinylidene fluoride membrane, printing paper, or nylon fiber cloth.

[0010] Furthermore, the patterned template is a screen or mask with a specific circuit pattern.

[0011] Furthermore, when the patterned template is a screen with a specific circuit pattern, it is coated by screen printing to form a patterned gel coating; when the patterned template is a mask with a specific circuit pattern, it is coated by spin coating or scraping coating to form a patterned gel coating.

[0012] Furthermore, the gallium-based liquid metal is selected from liquid pure gallium, liquid gallium-indium alloy, or liquid gallium-indium-tin alloy.

[0013] Furthermore, the coating method for the gallium-based liquid metal is selected from blade coating or roll coating.

[0014] Furthermore, the curing temperature is 25-80℃, and the time is 5-30 minutes.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: This invention utilizes a hydroxyl-rich gel solution to construct a smooth hydrophilic interface on a rough, flexible substrate surface, successfully solving the problem that gallium-based liquid metals cannot be directly spread on rough surfaces, thus broadening the selection range of liquid circuit substrates. By pre-defining the gel coating area using screen printing patterning technology, highly selective molding of liquid metal circuits is achieved. The hydroxyl groups of the gel coating are bonded to the gallium oxide on the liquid metal surface through strong hydrogen bonds, resulting in excellent adhesion between the circuit and the substrate, maintaining the circuit's integrity and conductivity even under bending and stretching conditions. The method provided by this invention requires simple equipment and uses low-cost gel raw materials, demonstrating significant commercial potential. Many hydroxyl-rich materials (such as polyvinyl alcohol and sodium alginate) possess good biocompatibility or biodegradability, making it possible to fabricate implantable or environmentally friendly electronic devices. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the process flow for fabricating gallium-based liquid metal patterned circuits using screen printing according to the present invention. Figure 2 (a) shows the gallium-based liquid metal patterned circuit prepared on printing paper in Example 1 and its scanning electron microscope image; (b) shows the resistance testing method of the conductive circuit in Example 1. Figure 3 Example 2 shows a gallium-based liquid metal patterned circuit fabricated on nylon fiber cloth. Figure 4 (a) is a scanning electron microscope image of gallium-based liquid metal patterned circuits fabricated on porous PVDF films in Example 3, and (b) is a schematic diagram of the resistance testing method of the conductive circuit in Example 3. Figure 5 This is a comparison of the gallium metal printing effect on the surface of ordinary printing paper with and without PVA gel solution in Comparative Example 1. Figure 6 This is a comparison of Galinstan metal droplet impact tests on uncoated and coated SA gel layers in Comparative Example 2. Figure 7 This is a schematic diagram showing gallium metal liquid rolling off the PE gel coating and PVA gel coating at the same angle in Comparative Example 3. Detailed Implementation

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0019] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0021] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0022] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0023] This invention provides a method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating, comprising the following steps: S1. Prepare a gel solution rich in hydroxyl groups; S2. On a rough, flexible substrate, the hydroxyl-rich gel solution is coated using a patterned template to form a patterned gel coating; S3. Gallium-based liquid metal is coated onto the patterned gel coating. The liquid metal selectively adheres to the gel coating area to form a patterned circuit. The gallium-based liquid metal outside the patterned gel coating is then removed. S4. Optionally, perform curing or drying treatment to enhance circuit stability.

[0024] In some preferred embodiments of the present invention, in step S1, the gelling substance in the hydroxyl-rich gel solution includes one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, and sodium alginate.

[0025] In some preferred embodiments of the present invention, in step S1, the concentration of the hydroxyl-rich gel solution is 8-20 wt.%.

[0026] In some preferred embodiments of the present invention, in step S2, the rough flexible substrate is selected from porous polyvinylidene fluoride membrane, printing paper or nylon fiber cloth.

[0027] In some preferred embodiments of the present invention, in step S2, the patterned template is a screen or mask with a specific circuit pattern; when the patterned template is a screen with a specific circuit pattern, it is coated by screen printing to form a patterned gel coating; when the patterned template is a mask with a specific circuit pattern, it is coated by spin coating or scraping coating to form a patterned gel coating.

[0028] In some preferred embodiments of the present invention, in step S3, the gallium-based liquid metal is selected from liquid pure gallium, liquid gallium-indium alloy, or liquid gallium-indium-tin alloy.

[0029] In some preferred embodiments of the present invention, in step S3, the coating method is scraping or roller coating.

[0030] In some preferred embodiments of the present invention, in step S4, the curing or drying process is carried out at a temperature of 25-80°C for 5-30 minutes.

[0031] Figure 1 This is a schematic diagram of the process flow for fabricating gallium-based liquid metal patterned circuits using screen printing according to the present invention.

[0032] The room temperature in this invention refers to 25±2℃.

[0033] Unless otherwise specified, all materials used in this invention are commercially available products.

[0034] Example 1 A method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating includes the following steps: S1. Prepare an 8 wt.% PVA (polyvinyl alcohol) aqueous solution and stir at 90°C until completely dissolved to obtain a transparent PVA gel solution; S2. Using a sheet of ordinary red printing paper as a rough, flexible substrate, a screen with a regular line pattern is placed over the printing paper. The PVA gel solution prepared in S1 is then printed onto the printing paper using a scraping method to form a serpentine gel coating. S3. Remove the screen and use a roller to evenly coat the entire substrate surface with EGaIn liquid gallium indium alloy (ga:in = 75.5:24.5). S4. Gently remove the gallium-based liquid metal outside the patterned gel coating with a lint-free cloth. It can be seen that the liquid metal is firmly adhered to the serpentine gel coating, forming a complete conductive circuit. S5. Dry at 60℃ for 10 min to remove excess moisture and enhance circuit stability, thus obtaining a gallium-based liquid metal patterned circuit.

[0035] Figure 2 (a) shows the gallium-based liquid metal patterned circuit prepared on printing paper in Example 1 and its scanning electron microscope image, and (b) shows the resistance testing method of the conductive circuit in Example 1.

[0036] The conductive circuit pattern obtained in this embodiment is clear, with a line width of approximately 1 mm.

[0037] The resistance of the circuit before bending was measured with a multimeter and recorded as R0. After bending repeatedly for 1000 times with a bending radius of 5mm, the resistance was measured and recorded as R. The resistance change rate = (R-R0) / R. The measured R0 was 18.5Ω, and the resistance change rate was <10%.

[0038] Example 2 A method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating includes the following steps: S1. Prepare an aqueous solution of SA (sodium alginate) with a concentration of 12 wt.% to obtain an SA gel solution; S2. Using nylon fiber cloth as a rough and flexible substrate, a mask with a wire pattern is used to cover the nylon fiber cloth. The SA gel solution is coated onto the mask using a spin coater to form a patterned gel coating. The mask is then removed. S3. Galinstan liquid gallium indium tin alloy (Ga∶In∶Sn=68.5:21.5:10 in gallium indium tin alloy) is uniformly coated onto the entire substrate surface using a scraper; S4. Remove gallium-based liquid metal outside the patterned gel coating by purging with nitrogen gas; S5. Dry at room temperature for 30 minutes to obtain a gallium-based liquid metal patterned circuit.

[0039] Figure 3 This is a gallium-based liquid metal patterned circuit prepared on nylon fiber cloth in Example 2. The circuit line width obtained in this example is 2 mm.

[0040] The tensile strength of the gallium-based liquid metal patterned circuit prepared in this embodiment was determined by the following method: The two ends of the nylon fiber cloth containing the gallium-based liquid metal patterned circuit were clamped into the upper and lower clamps of the tensile testing machine, respectively, to ensure that the axis of the sample was consistent with the tensile direction. The initial length L0 of the sample was recorded. The clamps were precisely displaced, and the length L of the sample after displacement was recorded. Then the uniaxial tensile strength = (L-L0) / L0.

[0041] Measurements showed that the gallium-based liquid metal patterned circuit prepared in this embodiment has a uniaxial stretchability of 50% and a resistance change rate of 15%, making it suitable for stretchable sensors.

[0042] Example 3 A method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating includes the following steps: S1. Prepare a 20 wt.% CMC (sodium carboxymethyl cellulose) aqueous solution to obtain a CMC gel solution; S2. Using a porous PVDF (polyvinylidene fluoride) membrane as a rough and flexible substrate, a screen with a regular circuit pattern is used to cover the PVDF porous membrane. The CMC gel solution prepared in S1 is printed onto the PVDF porous membrane by a scraping process to form a patterned gel coating. S3. Liquid pure gallium is rolled onto the substrate surface using rollers; S4. Gently vibrate and clean with a cotton swab to remove gallium-based liquid metal outside the patterned gel coating; S5. Curing at 80℃ for 5 minutes yields a gallium-based liquid metal patterned circuit.

[0043] Figure 4 Image (a) shows a scanning electron microscope image of a gallium-based liquid metal patterned circuit fabricated on a porous PVDF film in Example 3, and image (b) shows a schematic diagram of the resistance testing method for the conductive circuit in Example 3. The obtained circuit has a linewidth of 1 mm and a resistance of 29.1 Ω, exhibiting significant electrode heating effect and can be used to fabricate flexible electric heating elements.

[0044] Comparative Example 1 A method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating includes the following steps: S1. Prepare an 8 wt.% PVA (polyvinyl alcohol) aqueous solution and stir at 90°C until completely dissolved to obtain a transparent PVA gel solution; S2. Use a piece of ordinary red printing paper as a rough flexible substrate and divide it into two parts. Print the PVA gel solution prepared in S1 onto the printing paper in one part by scraping, and leave the other part uncoated with PVA gel coating. S3. Directly print the EGaIn liquid metal onto the two sections of printing paper mentioned above using a flexible printer; S4. Dry at 60℃ for 10 min.

[0045] Figure 5 This is a comparison of gallium metal printing effects on the surface of ordinary printing paper with and without PVA gel solution, as shown in Comparative Example 1. Figure 5 It can be seen that because the paper surface is rough, it cannot form continuous and effective hydrogen bonding with the liquid metal oxide film. The liquid metal cannot form continuous lines on the paper surface, but only discrete and irregular droplets, which cannot form a conductive path. In contrast, the printing paper coated with PVA forms a continuous conductive path.

[0046] Comparative Example 2 A method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating includes the following steps: S1. Prepare an aqueous solution of SA (sodium alginate) with a concentration of 12 wt.% to obtain an SA gel solution; S2. Using two nylon fiber cloths as rough flexible substrates, one of them is coated with SA gel solution by a spin coater to form an SA gel coating; the other is not pre-coated with SA gel. S3. Drop 10 μL of molten Galinstan onto the rough nylon fiber cloth and the SA gel coating, respectively.

[0047] Impact tests were conducted on the obtained Galinstan metal droplets, and the results are as follows: Figure 6 As shown, from Figure 6 As can be seen, due to the rough surface of the nylon fiber cloth, it cannot form continuous and effective hydrogen bonds with the liquid metal oxide film. Therefore, the liquid metal droplets cannot adhere to the surface of the nylon fiber cloth and exhibit a rebound behavior of completely detaching from the surface during the impact process. However, the nylon fiber cloth coated with SA gel coating exhibits a strong adhesion to the liquid metal droplets, preventing the droplets from detaching from the surface during the rebound process.

[0048] Comparative Example 3 A method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating includes the following steps: S1. Prepare PVA (polyvinyl alcohol) gel solution and PE (polyethylene) gel solution with a concentration of 8 wt.% respectively; S2. Using two porous PVDF membranes as rough flexible substrates, PVA gel solution and PE gel solution (non-hydroxy polymer) are coated onto the surface of the porous PVDF membranes by spin coating machine to form PVA gel coating and PE gel coating, respectively. S3. Place equal amounts of 50 μL gallium metal droplets on the two coatings and roll them off at the same angle.

[0049] Figure 7 As shown in the test results of Comparative Example 3, it can be seen that the PE gel coating lacks hydroxyl groups on its surface, resulting in no hydrogen bonding with the liquid metal oxide film. This causes gallium metal droplets to fail to adhere stably to the polyethylene coating, forming uneven rolling tracks and lacking the ability to form stable, continuous patterned circuits. In contrast, the PVA gel coating is rich in hydroxyl groups, enabling stable adhesion of liquid metal and the ability to form stable, uniform patterned circuits.

[0050] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating gallium-based liquid metal patterned circuits on a rough, flexible substrate using a hydroxyl-rich gel coating, characterized in that, The process includes the following steps: first, a patterned template is applied to a rough, flexible substrate, and then a gel solution rich in hydroxyl groups is applied to form a patterned gel coating; gallium-based liquid metal is applied to the patterned gel coating, the gallium-based liquid metal outside the patterned gel coating is removed, and after curing, a gallium-based liquid metal patterned circuit is formed.

2. The method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate using a hydroxyl-rich gel coating according to claim 1, characterized in that, The gelling substance in the hydroxyl-rich gel solution is selected from one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, and sodium alginate.

3. The method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate using a hydroxyl-rich gel coating according to claim 1, characterized in that, The concentration of the hydroxyl-rich gel solution is 8-20 wt.%.

4. The method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate using a hydroxyl-rich gel coating according to claim 1, characterized in that, The rough flexible substrate is selected from porous polyvinylidene fluoride membrane, printing paper, or nylon fiber cloth.

5. The method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate using a hydroxyl-rich gel coating according to claim 1, characterized in that, The patterned template is a screen or mask with a specific circuit pattern.

6. The method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate via a hydroxyl-rich gel coating according to claim 5, characterized in that, When the patterned template is a screen with a specific circuit pattern, it is coated by screen printing to form a patterned gel coating; when the patterned template is a mask with a specific circuit pattern, it is coated by spin coating or scraping coating to form a patterned gel coating.

7. The method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate using a hydroxyl-rich gel coating according to claim 1, characterized in that, The gallium-based liquid metal is selected from liquid pure gallium, liquid gallium-indium alloy, or liquid gallium-indium-tin alloy.

8. The method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate via a hydroxyl-rich gel coating according to claim 1, characterized in that, The coating method for the gallium-based liquid metal is selected from blade coating or roll coating.

9. The method for fabricating gallium-based liquid metal patterned circuits on a rough flexible substrate via a hydroxyl-rich gel coating according to claim 1, characterized in that, The curing temperature is 25-80℃, and the time is 5-30 minutes.

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