A method for preparing a reverse coffee ring structure surface

Abstract

The application discloses a preparation method of a reverse coffee ring structure surface. First, a solution of amidine functionalized microspheres is prepared, and a substrate is functionalized. Then, a coffee ring effect is inhibited by adding a water-soluble polymer to obtain a coffee ring glaze crystal template. Finally, nickel metal is electrodeposited on the surface of the template, and the template is dissolved to obtain the reverse coffee ring structure surface. The structure surface can be widely applied to the fields of heat pipe wick and phase change heat transfer surface.

Description

Technical Field

[0001] This invention belongs to the field of heat dissipation for electronic devices, and specifically relates to a method for preparing an inverted coffee ring structure surface. Background Technology

[0002] With the rapid development of electronic technology in fields such as defense communications, aerospace, and cultural life, electronic devices are experiencing a surge in popularity. Management issues are increasingly attracting researchers' attention. Heat pipes, as an important phase change heat transfer technology, have been widely used in smartphones, lithium batteries, and aerospace. The wick, as the core component of a heat pipe, is crucial to its heat dissipation capacity and also serves as an enhanced heat transfer surface. Compared to traditional heat transfer surfaces, a novel inverted coffee ring structure provides numerous nucleation sites and heat transfer area, and allows for timely liquid replenishment, effectively improving heat transfer performance. This structure has greater application prospects and market potential in heat pipe wicks and phase change heat transfer surfaces.

[0003] Currently, researchers both domestically and internationally primarily employ methods such as modifying the wick structure to improve the heat dissipation performance of heat pipes. Porous wicks are typically fabricated using methods such as screen printing, powder sintering, 3D printing, adding pore-forming agents, and metal foam. However, the resulting porous structures often have relatively large pore sizes, making them prone to closed pores and limiting nucleation sites. This can lead to "dry burning" at high heat flux densities. Given that inverse coffee ring structures possess advantages such as low pore size, numerous nucleation sites, and good liquid reflux, developing a simple and low-cost method for fabricating inverse coffee ring structures is of significant importance. Summary of the Invention

[0004] This invention provides a method for preparing an anti-coffee ring structure surface to solve the problems of existing methods having high equipment requirements and causing serious environmental pollution.

[0005] The technical solution to achieve the purpose of this invention is as follows: A method for preparing an anti-coffee ring structure surface includes the following steps: Step 1: Suppress the caffeine ring effect: The water-soluble polymer was dissolved in water at a certain temperature, and then an amidine-functionalized microsphere emulsion and glycerol were added. After stirring for a period of time and centrifuging and washing three times, a microsphere emulsion encapsulating the polymer was obtained. This emulsion was then dropped onto the central region of a functionalized silicon substrate to obtain a colloidal template that suppresses the coffee ring effect. Step 2, Electrodeposition of Nickel: A functionalized silicon substrate with a gel crystal template is rapidly transferred to a nickel electroplating solution, connected to a power source for deposition, and then left to stand in an organic solvent for a period of time to dissolve the gel crystal template, resulting in a single-ring inverse coffee ring structure surface.

[0006] A method for preparing an anti-coffee ring structure surface includes the following steps: Step 1: Suppress the caffeine ring effect: A water-soluble polymer was dissolved in water at a certain temperature, and an amidine-functionalized microsphere emulsion was added. Glycerin was added, and the mixture was kept warm and stirred for a period of time. After centrifugation and washing three times, a polymer-encapsulated microsphere emulsion was obtained. Then, it was dropped onto the central area of ​​a functionalized silicon substrate and allowed to stand for more than 30 minutes. Then, the polymer-encapsulated microsphere emulsion was dropped onto the dropping area to obtain a colloidal template that suppresses the coffee ring effect. Step 2, Electrodeposition of Nickel: A functionalized silicon substrate with a gel crystal template is rapidly transferred to a nickel electroplating solution, connected to a power source for deposition, and then left to stand in an organic solvent for a period of time to dissolve the gel crystal template, resulting in a double-ring inverse coffee ring structure surface.

[0007] Preferably, the amidine-functionalized microspheres are prepared by the following steps: dispersing polydiallyldimethylammonium chloride solution and styrene solution in anhydrous ethanol, performing deoxygenation treatment, injecting the deoxygenated 2,2-azobis(2-methylpropanemidine) hydrochloride solution, heating and stirring, and after complete reaction, centrifuging, washing, and drying to obtain amidine-functionalized microspheres.

[0008] Preferably, the particle size of the amidine-functionalized microspheres is 740~750nm.

[0009] Preferably, the amidine-functionalized microspheres are placed in water to obtain an amidine-functionalized microsphere emulsion with a concentration of 0.5 wt%.

[0010] Preferably, the functionalized substrate silicon wafer is obtained through the following steps: the silicon wafer is ultrasonically washed in methanol, acetone and isopropanol respectively, then heated and modified in an alkaline piranha solution, and then immersed in an N-(3-(trimethoxysilyl)propyl)-N,N,N-trimethylammonium chloride methanol solution to make it positively charged. After cleaning, the functionalized substrate silicon wafer is obtained, wherein, by volume ratio, H2O2:NH4OH:H2O=1:1:5 in the alkaline piranha solution.

[0011] Preferably, the size of the functionalized substrate silicon wafer is 1*1cm.

[0012] Preferably, the water-soluble polymer is PVA, and the mass ratio of amidine-functionalized microspheres to water-soluble polymer is 20000:3.

[0013] Preferably, the concentration of the water-soluble polymer solution obtained by dissolving the water-soluble polymer in water at a certain temperature is... It is 1 g / L.

[0014] Preferably, the water-soluble polymer is dissolved in water at 80°C, and then an amidine-functionalized microsphere emulsion is added. Glycerin is added, and the mixture is kept warm and stirred for 2 hours. The amount of glycerin added is 0.06% of the volume of the amidine-functionalized microsphere emulsion.

[0015] Preferably, the amount of polymer-encapsulated microsphere emulsion added is 1~2 μL.

[0016] A preferred nickel plating solution is: Ni(SO3NH2)2 13wt%, NiBr2 0.7wt%, H3BO3 2.26wt%, pH 3.5~4.

[0017] Preferably, the deposition current is 5 mA / cm2, the deposition temperature is 25℃, and the deposition time is 0.5~1h.

[0018] Preferably, the organic solvent is toluene, and the mixture is allowed to stand for 24 hours.

[0019] Compared with the prior art, the present invention has the following significant advantages: (1) The preparation method of the present invention is simple, low in cost and has little environmental pollution.

[0020] (2) The surface of the inverse coffee ring structure prepared by the present invention has enhanced heat transfer characteristics and has great application prospects and market potential in the fields of heat pipe wicks and phase change heat transfer surfaces.

[0021] (3) This invention realizes the reverse growth of the template for suppressing the coffee ring effect, which is beneficial to the development and utilization of evaporators.

[0022] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation process of the anti-coffee ring structure surface.

[0024] Figure 2 This is a schematic diagram illustrating the preparation of the anti-coffee ring structure surface.

[0025] Figure 3 Scanning electron microscope images of self-assembled microsphere templates: (a) with cracks, (b) without cracks.

[0026] Figure 4Scanning electron microscopy (a-f) and microscopic images (a′-f′) of coffee rings formed from mixed droplets: (a) and (a′) 0.5 wt% amidine-functionalized microsphere emulsion; (b) and (b′) 0.5 wt% amidine-functionalized microsphere emulsion + 0.1 g / L PVA; (c) and (c′) 0.5 wt% amidine-functionalized microsphere emulsion + 0.5 g / L PVA; (d) and (d′) 0.5 wt% amidine-functionalized microsphere emulsion + 1 g / L PVA; (e) and (e′) 0.5 wt% amidine-functionalized microsphere emulsion + 1.5 g / L PVA; (f) and (f′) 0.5 wt% amidine-functionalized microsphere emulsion + 2 g / L PVA.

[0027] Figure 5 Microscopic images of the surface of the inverted coffee ring structure, (a) 1st time, (b) 2nd time, (c) 3rd time.

[0028] Figure 6 The images show the full scanning electron microscope (SEM) views of the surface of the single-ring inverse coffee ring structure (a) in Example 1 and the surface of the double-ring inverse coffee ring structure (b) in Example 2.

[0029] Figure 7 The images are partial scanning electron microscope (SEM) images of the surface of the inverted coffee ring structure: (a) 200 μm, (b) 50 μm, (c) 10 μm, and (d) 5 μm.

[0030] Figure 8 The phase change heat test curves are shown for the surface of the inverse coffee ring structure, (a) single ring, (b) double ring. Detailed Implementation

[0031] To illustrate the technical solution and objectives of this invention, the invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0032] This invention increases droplet viscosity by adding a water-soluble polymer additive to an amidine-functionalized microsphere emulsion, preventing fluid from flowing outward from the droplet center. This avoids the formation of a coffee ring structure, resulting in a relatively uniform drying pattern and achieving an anti-coffee ring structure. Figure 2 This is a schematic diagram illustrating the fabrication of an inverse coffee ring structure surface. After suppressing the coffee ring effect, the coffee ring surface formed by the liquid on the silicon surface is relatively uniform, but the deposition thickness of the outer ring microspheres is slightly higher than that of the interior. The structure at the junction of the outer and interior rings is unstable. If a nickel-based inverse opal structure surface is fabricated by electrodeposition, the originally unstable area will not have a metal structure deposited, instead exposing the substrate. This exposed substrate splits the structure surface into an outer ring and an inner ring. The exposed portion between the outer and inner rings provides space for liquid reflux and enhances local disturbance. Except for the exposed substrate portion, the remaining structure is a nickel-based inverse opal structure. Example 1

[0033] Combination Figure 1 A method for preparing an anti-coffee ring structure heat exchange surface includes the following steps: Step 1: Preparation of amidine-functionalized microsphere emulsion: Measure 0.13 ml of 28% polydiallyldimethylammonium chloride solution and 6 ml of styrene solution, pour them into a round-bottom flask containing 75 ml of anhydrous ethanol, purge with nitrogen to remove oxygen, then inject 0.07 g of the deoxygenated 2,2-azobis(2-methylpropanediamine) hydrochloride solution, heat to 75 °C and stir for 20 hours. After the reaction is complete, centrifuge and wash for later use.

[0034] Step 2, Functionalizing the silicon substrate: The silicon wafer was ultrasonically treated in methanol, acetone and isopropanol for 15 minutes each, then immersed in an alkaline piranha solution at 80°C for 3 hours, followed by immersion in a 1.0% N-[3-(trimethoxysilyl)propyl]-N,N,N-trimethylammonium chloride solution for 24 hours, and finally thoroughly rinsed with deionized water.

[0035] Step 3: Eliminate cracks After the amidine-functionalized microsphere emulsion prepared in step 1 was dropped onto the functionalized silicon substrate prepared in step 2, and allowed to stand for 30 minutes, the substrate was observed using a scanning electron microscope. Figure 3 As shown in Figure a, when the prepared microsphere emulsion is deposited onto the substrate for self-assembly, a large number of dense cracks appear on the template, leading to an inverted crack structure after electrodeposition, hindering the uniform distribution of pores and blocking fluid transport. To eliminate the cracks, glycerol at a concentration of 0.06% v / v was added to the amidine-functionalized microsphere emulsion, and then it was dropped onto the functionalized silicon substrate. After standing for 30 min, the substrate was observed by scanning electron microscopy. Figure 3 As shown in b, the template cracking problem has been effectively alleviated. Furthermore, the addition of the humectant glycerin does not affect the self-assembly and cubic structure of the particles.

[0036] Step 4: Suppress the caffeine ring effect: To compare the degree of inhibition of the coffee ring effect under different concentrations of PVA, 0 g / L, 0.1 g / L, 0.5 g / L, 1 g / L, 1.5 g / L, and 2 g / L PVA solutions were prepared at 80 °C. These solutions were then added to a 0.5% (w / w) amidine-functionalized microsphere emulsion (containing 0.06% v / v glycerol). After incubation and stirring for 2 h, the microspheres were centrifuged and washed three times to obtain polymer-encapsulated microsphere emulsions (the purpose of repeating centrifugation and washing three times was to bring the surface tension close to the value when no water-soluble polymer was added). Subsequently, 1-2 μL of each polymer-encapsulated microsphere emulsion was dropped onto the central region of a 1*1 cm functionalized silicon substrate to obtain a colloidal template for inhibiting the coffee ring effect. The scanning electron microscope (SEM) and microscopic images are shown below. Figure 4 As shown, the coffee ring outer ring formed when 1 g / L PVA solution is added almost disappears, and the coffee ring effect is successfully suppressed. Therefore, the microsphere emulsion encapsulating 1 g / L PVA is used as the colloidal template for preparing the surface of the monocyclic anti-coffee ring structure, denoted as colloidal template A.

[0037] To verify the effect of the number of centrifugal washing cycles on the uniformity of the distribution of amidine-functionalized microsphere emulsion on the functionalized silicon substrate, polymer-encapsulated microsphere emulsions (1 g / L PVA solution + 0.5 wt% amidine-functionalized microsphere emulsion) were obtained after centrifugal washing once, twice, and three times, respectively. These emulsions were then dropped onto the central region of the functionalized silicon substrate to obtain a colloidal template that suppresses the coffee ring effect. The microscopic image is shown below. Figure 5 As shown.

[0038] Step 5, Electrodeposition of Nickel: Step 5.1: Quickly immerse the gel crystal template A into the nickel plating solution, tilting it downwards. Connect the power supply to the template and the nickel anode, and apply a constant current at 5 mA / cm². 2 The nickel plating solution was deposited at a current density of 13 wt%, NiBr2 0.7 wt%, H3BO3 2.26 wt%, and pH 3.5~4.

[0039] Step 5.2: After electrodepositing nickel, the template is soaked in toluene for more than 10 hours to dissolve the template and form a single-ring inverse coffee ring structure surface.

[0040] Figure 6 In the image, 'a' is a scanning electron microscope (SEM) image of the surface of the single-ring inverse coffee ring structure. Figure 7 This is a partial scanning electron microscope (SEM) image of the surface of a single-ring inverted coffee ring structure. The exposed portion between the outer and inner rings provides space for liquid reflux and enhances local disturbance, thereby improving heat transfer. The critical heat flux density of the silicon-based reference surface is approximately 48.6 W / cm². 2 The heat transfer coefficient is approximately 1.72 W / (cm²).2 ·K). Figure 8 In the figure, 'a' represents the phase change heat transfer performance curve of the surface of a single-ring inverse coffee ring, indicating that the critical heat flux density of the single-ring inverse coffee ring surface is 96.4 W / cm². 2 The heat transfer coefficient is 3.9 W / (cm²). 2 ·K).

[0041] Example 2

[0042] Steps 1 and 2 are the same as in Example 1.

[0043] Step 3: At 80℃, prepare a 1 g / L PVA solution, add 0.5% amidine-functionalized microsphere emulsion, add glycerol (the amount of glycerol added is 0.06 v% of the amidine-functionalized microsphere emulsion), keep warm and stir for 2 h, centrifuge and wash 3 times to obtain a polymer-encapsulated microsphere emulsion, then drop 1-2 μL onto the central area of ​​a 1*1 cm functionalized silicon substrate wafer, let stand for more than 30 min, and then continue to drop 1-2 μL onto the drop area to obtain a colloidal template that suppresses the coffee ring effect; Step 4, the same as step 5 in Example 1, yields a double-ring inverted coffee ring structure surface.

[0044] Figure 8 In the figure, b represents the phase change heat transfer performance curve of the surface of the bicyclic inverse coffee ring, and it can be seen that the critical heat flux density of the surface of the bicyclic inverse coffee ring is 136.8 W / cm². 2 The critical heat flux density on the surface of a double-ring inverse coffee ring is higher than that on the surface of a single-ring inverse coffee ring; the heat transfer coefficient on the surface of a double-ring inverse coffee ring is 5.0 W / (cm²). 2 The heat transfer coefficient of the double-ring structure is higher than that of the single-ring structure (K). This may be because the surface of the double-ring inverse coffee ring has more vaporization nuclei than that of the single-ring inverse coffee ring, which is more conducive to enhancing the vapor-liquid phase change heat transfer characteristics.

Claims

1. A method for preparing an anti-coffee ring structure surface, characterized in that, Includes the following steps: Step 1: Suppress the caffeine ring effect: A water-soluble polymer PVA was dissolved in water at a certain temperature to obtain a water-soluble polymer solution with a concentration of 1 g / L. Amidine-functionalized microsphere emulsion was added, along with glycerol. After incubation and stirring for a period of time, the surface tension was centrifuged and washed three times to make it approach the state value when no water-soluble polymer was added, thus obtaining a polymer-encapsulated microsphere emulsion. Subsequently, it was dropped onto the central region of a functionalized silicon substrate to obtain a colloidal template that suppresses the coffee ring effect. Step 2, Electrodeposition of Nickel: A functionalized silicon substrate with a gel crystal template is rapidly transferred to a nickel electroplating solution, connected to a power source for deposition, and then left to stand in an organic solvent for a period of time to dissolve the gel crystal template, resulting in a single-ring inverse coffee ring structure surface.

2. A method for preparing an anti-coffee ring structure surface, characterized in that, Includes the following steps: Step 1: Suppress the caffeine ring effect: A water-soluble polymer PVA was dissolved in water at a certain temperature to obtain a water-soluble polymer solution with a concentration of 1 g / L. Amidine-functionalized microsphere emulsion was added, along with glycerol. After incubation and stirring for a period of time, the surface tension was centrifuged and washed three times to make it approach the state value when no water-soluble polymer was added, thus obtaining a polymer-encapsulated microsphere emulsion. This emulsion was then dropped onto the central region of a functionalized silicon substrate and allowed to stand for more than 30 minutes. The polymer-encapsulated microsphere emulsion was then dropped onto the dropping area to obtain a colloidal template that suppresses the coffee ring effect. Step 2, Electrodeposition of Nickel: A functionalized silicon substrate with a gel crystal template is rapidly transferred to a nickel electroplating solution, connected to a power source for deposition, and then left to stand in an organic solvent for a period of time to dissolve the gel crystal template, resulting in a double-ring inverse coffee ring structure surface.

3. The method as described in claim 1 or 2, characterized in that, The amidine-functionalized microspheres were prepared by the following steps: a polydiallyldimethylammonium chloride solution and a styrene solution were dispersed in anhydrous ethanol and deoxygenated. The deoxygenated 2,2-azobis(2-methylpropanemidine) hydrochloride solution was then injected, heated and stirred, and after complete reaction, the mixture was centrifuged and washed to obtain amidine-functionalized microspheres.

4. The method as described in claim 1 or 2, characterized in that, Amidine-functionalized microspheres were placed in water to obtain an amidine-functionalized microsphere emulsion with a concentration of 0.5 wt%.

5. The method as described in claim 1 or 2, characterized in that, Functionalized substrate silicon wafers are obtained through the following steps: the silicon wafers are ultrasonically washed in methanol, acetone and isopropanol respectively, then heated and modified in an alkaline piranha solution, and then immersed in an N-(3-(trimethoxysilyl)propyl)-N,N,N-trimethylammonium chloride methanol solution to make them positively charged. After cleaning, functionalized substrate silicon wafers are obtained. In the alkaline piranha solution, the volume ratio of H2O2:NH4OH:H2O is 1:1:

5.

6. The method as described in claim 1 or 2, characterized in that, The mass ratio of amidine-functionalized microspheres to water-soluble polymer is 20000:

3.

7. The method as described in claim 1 or 2, characterized in that, The water-soluble polymer was dissolved in water at 80°C, and then amidine-functionalized microsphere emulsion and glycerol were added. The mixture was kept warm and stirred for 2 hours. The amount of glycerol added was 0.06% of the volume of amidine-functionalized microsphere emulsion.

8. The method as described in claim 1 or 2, characterized in that, The nickel plating solution consists of: Ni(SO3NH2)2 13wt%, NiBr2 0.7wt%, H3BO3 2.26wt%, and pH 3.5~4.

9. The method as described in claim 1 or 2, characterized in that, Deposition current is 5 mA / cm 2 The deposition temperature was 25℃, and the deposition time was 0.5~1h.

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