A method of inhibiting the coffee ring effect

Abstract

The present application relates to the technical field of coating, in particular to a method for inhibiting coffee ring effect. The present application is based on the synergistic effect of gravity affecting the distribution of solid particles in a liquid containing particles, solvent surface tension and evaporation rate to inhibit coffee ring effect. The present application adopts a specific drying method of inverting the wet coating layer downward. Under the influence of gravity, the liquid droplets form an inverted cone, and the solid particles are affected by gravity and concentrated at the bottom of the cone. The solid particles flowing to the edge flow downward after reaching the edge, and the cycle continues, so that the solid particles gradually dry and fix to the substrate surface. By controlling the volume fraction of volatile organic solvent in the solvent and the drying temperature, the control of the solvent surface tension and the evaporation rate is realized, and the coffee ring effect is effectively inhibited, and a uniform coating is obtained. The method provided by the present application is simple and effective, and is suitable for different substrate surfaces, solvents and solid particles, and has wide application range and wide application scenarios.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coating technology, and in particular to a method for inhibiting coffee ring effect. BACKGROUND

[0002] Coffee ring effect (CRE) is essentially a kind of material transport and deposition phenomenon dominated by capillary flow and contact line pinning. Specifically, when a drop of liquid containing particles evaporates on a solid surface, two key processes occur: (1) contact line pinning: the edge of the liquid drop (three-phase contact line) is fixed and cannot retract; (2) uneven evaporation: the evaporation rate of the edge of the liquid drop (pinning site) is much higher than that of the central region. In order to make up for the liquid evaporated at the edge, a capillary flow (also known as a replenishment flow) from the center to the edge will be generated inside the liquid drop. This flow will bring the particles dispersed in the liquid drop to the edge. When the liquid is finally completely evaporated, the particles are accumulated at the edge, forming a typical "coffee ring". Coffee ring effect can cause the coating to accumulate at the boundary, forming an uneven distribution of thick edges and thin centers, affecting the thickness, uniformity, adhesion, and other performance of the coating, such as corrosion and pollution resistance, impact resistance, hardness, etc.

[0003] Currently, the methods for inhibiting coffee ring effect mainly include: (1) adding a surfactant: by inducing Marangoni convection to counteract and offset the capillary flow leading to coffee ring, thereby inhibiting coffee ring effect; (2) changing the shape of the particles: spherical particles have small flow resistance in the liquid and are very easy to be carried by capillary flow, smoothly reaching the edge and depositing, while non-spherical particles (such as ellipsoidal, rod-shaped, sheet-shaped, chain-shaped, etc.) have large geometric resistance, which can disrupt the smooth transport of particles to the edge, thereby inhibiting coffee ring effect; (3) using an oily cover layer: basically eliminating directional capillary flow, particles rely on diffusion and gravity settling, thereby inhibiting coffee ring effect. Although the above methods can effectively inhibit coffee ring effect, they have high cost and complex steps, which limits the application scenarios of the above methods. SUMMARY

[0004] In view of this, the purpose of the present application is to provide a method for inhibiting coffee ring effect. The method for inhibiting coffee ring effect provided by the present application is simple to operate, low in cost, and widely applicable.

[0005] In order to achieve the above-mentioned application purpose, the present application provides the following technical solutions:

[0006] The application provides a method for inhibiting coffee ring effect, comprising the following steps: coating a mixed solution on a substrate surface to form a wet coating layer, inverting the wet coating layer to make the wet coating layer face downward, and drying to obtain a coating layer which inhibits coffee ring effect; the mixed solution containing particles comprises solid particles and a solvent; the solvent comprises water or a volatile organic solvent aqueous solution, and the volume fraction of the volatile organic solvent in the volatile organic solvent aqueous solution is less than or equal to 50%; and the drying temperature is 20-140 DEG C.

[0007] Preferably, the maximum coating amount of the mixed solution containing particles is such that no liquid drops when the wet coating layer is inverted.

[0008] Preferably, the volatile organic solvent comprises at least one of a lower alcohol, an amide solvent, an ester solvent and a ketone solvent.

[0009] Preferably, the lower alcohol comprises methanol and / or ethanol.

[0010] The amide solvent comprises N, N-dimethylformamide.

[0011] Preferably, the mass concentration of the solid particles in the mixed solution containing particles is 0.1-20%.

[0012] Preferably, the particle size of the solid particles is 0.01-10 microns.

[0013] Preferably, the solid particles comprise one or more of a metal element, an oxide, a metal salt, a polymer and a carbon material; and the solid particles are insoluble in water.

[0014] Preferably, the metal element comprises one or more of copper, iron, gold, cobalt, nickel and silver.

[0015] The oxide comprises a metal oxide and / or a non-metal oxide; the metal oxide comprises one or more of aluminum oxide, magnetite, magnesium oxide and manganese oxide; and the non-metal oxide comprises silicon oxide and / or boron nitride.

[0016] The metal salt comprises one or more of calcium carbonate, magnesium hydroxide and silver chloride.

[0017] The polymer comprises one or more of covalent organic framework material, ion porous organic polymer, cellulose, epoxy resin, phenolic resin and polythiophene.

[0018] The carbon material comprises one or more of carbon particles, carbon nanotubes, graphene and graphite particles.

[0019] Preferably, the substrate comprises an electrically conductive material or an insulating material.

[0020] Preferably, the conductive material comprises a metallic electrode, a non-metallic electrode or conductive glass.

[0021] The insulating material comprises non-conductive glass, ceramic, wood, plastic or paper.

[0022] The present application is based on the synergistic effect of gravity affecting the distribution of solid particles in the liquid containing particles, the surface tension of the solvent and the evaporation speed to inhibit the coffee ring effect. Specifically, the present application adopts the drying method of inverting the wet coating layer downward. Under the influence of gravity, the liquid droplets containing particles will form an inverted cone, and the solid particles will be concentrated at the bottom of the cone due to the influence of gravity, so that the solid particles flowing to the edge will flow downward after reaching the edge, and so on, so that the solid particles are gradually dried and fixed to the surface of the substrate, effectively inhibiting the coffee ring effect and obtaining a uniform coating. If the volume fraction of volatile organic solvents in the solvent is too high, the surface tension of the solution will decrease, which will reduce the amount of liquid droplets that will not fall when inverted on the surface, and also cause the liquid droplets to evaporate faster. Then the particles in the solution may not have enough time to circulate in the liquid, resulting in accumulation at the edge and increasing the coffee ring effect. Due to gravity, the particles at the edge of the droplet will flow away from the edge to the middle, and then due to surface tension, the particles will flow to the edge again, and so on, gradually drying, so that the particles are evenly dried on the surface of the solid, thereby inhibiting the coffee ring effect. If the solvent evaporates too quickly, it will disrupt this process, causing the particles to dry before they have had a chance to circulate, resulting in a more pronounced coffee ring effect. By controlling the volume fraction of volatile organic solvents in the solvent and the drying temperature, the present application can adjust the surface tension of the solvent, and then control the internal flow pattern of the liquid droplets containing particles during evaporation, converting the "outward" flow that is replenished from the edge to the center to "inward" or "uniform" flow from the center to the edge or uniformly, thereby evenly distributing the solid particles throughout the contact area of the droplet, rather than just accumulating at the edge, thereby effectively inhibiting the coffee ring effect. Moreover, the method provided by the present application does not require any changes to the properties of the two ends of the drying interface, but only requires the use of a specific drying method of wet coating layer facing downward during drying to effectively inhibit the coffee ring effect. The method provided by the present application is simple and effective, and is not affected by equipment, suitable for different types of substrates, different types of solvents and different types of solid particles, and has a wide range of applications. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a digital photograph of the original glassy carbon electrode;

[0024] Figure 2 is a digital photograph of the glassy carbon electrode with a coating in Examples 2-4 and Comparative Example 1;

[0025] Figure 3Digital photograph of a glassy carbon electrode with a coating for Comparative Examples 2-4;

[0026] Figure 4 Digital photograph of a glassy carbon electrode with a coating for Examples 5-9 and Comparative Example 5;

[0027] Figure 5 Digital photograph of a common glass surface with a coating for Examples 10-12;

[0028] Figure 6 Digital photograph of a glassy carbon electrode with a coating for Examples 13-15;

[0029] Figure 7 Digital photograph of a gold electrode with a coating for Examples 16-18 and a bare gold electrode;

[0030] Figure 8 Digital photograph of a paper with a coating for Example 19 and Comparative Example 5. DETAILED DESCRIPTION

[0031] The present application provides a method for inhibiting coffee ring effect, comprising the following steps: applying a liquid containing particles on a substrate surface to form a wet coating surface, inverting the wet coating surface to face downward, and drying to obtain a coating that inhibits coffee ring effect; the liquid containing particles comprises solid particles and a solvent; the solvent comprises water or a volatile organic solvent aqueous solution, the volume fraction of the volatile organic solvent in the volatile organic solvent aqueous solution is ≤50%; the drying temperature is 20-140°C.

[0032] Unless otherwise specified, the materials and equipment used in the present application are commercially available in the art.

[0033] In the present application, the volatile organic solvent can comprise at least one of a lower alcohol, an amide solvent, an ester solvent, and a ketone solvent; the lower alcohol can comprise methanol and / or ethanol; the amide solvent can comprise N,N-dimethylformamide (DMF); the ester solvent can comprise ethyl acetate; and the ketone solvent can comprise acetone. In the present application, the volume fraction of the volatile organic solvent in the volatile organic solvent aqueous solution is ≤50%, which can be ≤20%, and can be specifically 0.01%, 0.1%, 0.5%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0034] In the present application, the mass concentration of the solid particles in the liquid containing particles can be 0.1-20%, and can also be 0.5-5%, and can be specifically 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 18% or 20%.

[0035] In the present application, the particle size of the solid particles can be 0.01-10 μm, and can also be 0.1-10 μm, and can further be 0.5-5 μm, and can be specifically 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0036] In the present application, the solid particles include one or more of metal elements, oxides, metal salts, polymers and carbon materials; the solid particles are insoluble in water. In the present application, the metal elements can include one or more of copper, iron, gold, cobalt, nickel and silver. In the present application, the oxides can include metal oxides and / or non-metal oxides; the metal oxides can include one or more of aluminum oxide, magnetite, magnesium oxide and manganese oxide; the non-metal oxides include silicon oxide and / or boron nitride. In the present application, the metal salts can include one or more of calcium carbonate, magnesium hydroxide and silver chloride. In the present application, the polymers include one or more of covalent organic framework materials, ionically porous organic polymers, cellulose, epoxy resin, phenolic resin and polythiophene. In the present application, the carbon materials can include one or more of carbon particles, carbon nanotubes, graphene and graphite particles.

[0037] In the present application, the substrate can include conductive materials or insulating materials. In the present application, the conductive materials can include metal electrodes, non-metal electrodes or conductive glass (ITO); the metal electrodes include gold electrodes or platinum electrodes; the non-metal electrodes include glassy carbon electrodes or graphite electrodes. In the present application, the insulating materials can include non-conductive glass, ceramics, wood, plastics or paper.

[0038] In the present application, the liquid containing particles can be uniformly dispersed before use; the dispersion methods include stirring dispersion and / or ultrasonic dispersion. The present application does not have special limitations on the coating method and coating amount of the liquid containing particles, which can be determined according to actual needs. In specific embodiments of the present application, the coating method is dropwise addition, and the coating amount is determined by the fact that liquid droplets do not drip when inverted.

[0039] In the present application, the inversion can be placing the substrate with the wet coating surface on a support, with the wet coating surface facing downward.

[0040] In the present application, the drying temperature is 20-140℃, can be 20-100℃, can also be 40-80℃, can be specifically 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃ or 140℃; the present application does not have special limitation to the drying time, and drying until the solvent is completely evaporated can be used.

[0041] In order to further illustrate the present application, the method for inhibiting coffee ring effect provided by the present application is described in detail below in combination with examples, but they should not be understood as limiting the protection scope of the present application.

[0042] Example 1

[0043] Preparation of polymer particles (carbon-porous organic polymer composite, denoted as IPOPs@C): 1.8 mmol of (1-imidazolyl)acetonitrile (AC-MI) and 5.4 mmol of 4,4'-bis(chloromethyl) biphenyl (BCMBP) were dissolved in 40 mL of 1,2-dichloroethane (DCE), and quaternary ammonium was reacted at 80℃ for 10 h, conductive carbon black was added and stirred for 30 min, 5.4 mmol of anhydrous FeCl3 was added, and the reaction was continued at 80℃ for 12 h, methanol was used as a solvent Soxhlet extraction for 12 h, and then drying was carried out at 90℃ for 10 h to obtain carbon-porous organic polymer composite (IPOPs@C). The mass of conductive carbon black is 2% of the total mass of (1-imidazolyl)acetonitrile and 4,4'-bis(chloromethyl) biphenyl.

[0044] Example 2

[0045] The polymer particles (IPOPs@C) prepared in Example 1 were uniformly dispersed using deionized water to obtain a mixed solution with a concentration of 1 mg / mL. The mixed solution was added dropwise on the surface of a glassy carbon electrode to form a wet coating layer, and then placed upside down (wet coating layer facing down) on a support and dried at 30℃ to obtain a coating layer for inhibiting coffee ring effect.

[0046] Example 3

[0047] The difference from Example 2 is only that the drying temperature is 50℃.

[0048] Example 4

[0049] The difference from Example 2 is only that the drying temperature is 80℃.

[0050] Comparative Example 1

[0051] The difference from Example 2 is only that the drying temperature is 150℃.

[0052] Comparative Example 2

[0053] The difference from Example 2 is only that the drying is done with the right side up (i.e. the wet coating facing up).

[0054] Comparative Example 3

[0055] The difference from Example 3 is only that the drying is done with the right side up.

[0056] Comparative Example 4

[0057] The difference from Example 4 is only that the drying is done with the right side up.

[0058] Example 5

[0059] The difference from Example 3 is only that the solvent is 20 vol% ethanol - deionized water.

[0060] Example 6

[0061] The difference from Example 3 is only that the solvent is 20 vol% methanol - deionized water.

[0062] Example 7

[0063] The difference from Example 3 is only that the solvent is 20 vol% N,N-dimethylformamide (DMF) - deionized water.

[0064] Example 8

[0065] The difference from Example 3 is only that the solvent is 30 vol% ethanol - deionized water.

[0066] Example 9

[0067] The difference from Example 3 is only that the solvent is 50 vol% ethanol - deionized water.

[0068] Comparative Example 5

[0069] The difference from Example 3 is only that the solvent is 80 vol% ethanol - deionized water.

[0070] Example 10

[0071] Aluminum trioxide (particle size 50 nm) is dispersed uniformly using deionized water to obtain a mixture with a concentration of 2 mg / mL. The mixture is added dropwise to the surface of a common glass, inverted on a support, and dried at 50°C to obtain a coating that suppresses the coffee ring effect.

[0072] Example 11

[0073] The difference from Example 10 is only that the concentration of the mixture is 1 mg / mL.

[0074] Example 12

[0075] The difference from Example 11 is that the concentration of the mixed solution is 1 mg / mL and the drying temperature is 100℃.

[0076] Example 13

[0077] Aluminum oxide (50 nm in particle size) is uniformly dispersed in deionized water to obtain a mixed solution with a concentration of 1 mg / mL. The mixed solution is dropped on the surface of a glassy carbon electrode, and the glassy carbon electrode is placed upside down on a support and dried at 30℃ to obtain a coating that suppresses the coffee ring effect.

[0078] Example 14

[0079] The difference from Example 13 is that the drying temperature is 50℃.

[0080] Example 15

[0081] The difference from Example 13 is that the drying temperature is 80℃.

[0082] Example 16

[0083] The polymer particles (IPOPs@C) prepared in Example 1 are uniformly dispersed in deionized water to obtain a mixed solution with a concentration of 1 mg / mL. The mixed solution is dropped on the surface of a gold electrode, and the gold electrode is placed upside down on a support and dried at 50℃ to obtain a coating that suppresses the coffee ring effect.

[0084] Example 17

[0085] The difference from Example 16 is that the solvent is 50 vol% ethanol-deionized water.

[0086] Example 18

[0087] The difference from Example 16 is that the drying temperature is 100℃.

[0088] Example 19

[0089] The difference from Example 16 is that the substrate is paper.

[0090] Comparative Example 6

[0091] The difference from Example 19 is that the glassy carbon electrode is placed right side up during drying.

[0092] Figure 1 The digital photograph of the original glassy carbon electrode is, Figure 2 The digital photograph of the glassy carbon electrode with a coating in Examples 2-4 and Comparative Example 1 is, Figure 3 The digital photograph of the glassy carbon electrode with a coating in Comparative Examples 2-4 is, Figures 1-3 It can be seen that placing the glassy carbon electrode upside down is conducive to weakening the coffee ring effect, and that too high a temperature will make the weakening effect worse.

[0093] Figure 4 The digital photo of the glass electrode with coating in Examples 5-9 and Comparative Example 5 is shown in Figure 1. Figure 2 The digital photo of the glass electrode with coating in Examples 5-9 and Comparative Example 5 is shown in Figure 1. Figure 4 It can be seen that the effect of various organic solvents and the effect of the concentration of ethanol on the effect are compared, and under the conditions of the organic solvent and the appropriate concentration, the surface without the coffee ring effect can be obtained, and the weakening effect will be poor with the increase of the concentration of the organic solvent.

[0094] Figure 5 The digital photo of the general glass surface with coating in Examples 10-12 is shown in Figure 2. Figure 5 It can be seen that the method provided by the application is suitable for the glass surface, the concentration in the solution has no obvious influence, and a wide concentration range can be compatible; the temperature has a relatively obvious influence on the coffee ring effect, and the weakening of the coffee ring effect will be poor with the temperature being too high.

[0095] Figure 6 The digital photo of the glass electrode with coating in Examples 13-15 is shown in Figure 3. Figure 6 It can be seen that the temperature has a relatively obvious influence on the coffee ring effect, and the weakening of the coffee ring effect will be poor with the temperature being too high.

[0096] Figure 7 The digital photo of the gold electrode with coating in Examples 16-18 is shown in Figure 4. Figure 7 It can be seen that the method of the application is suitable for the metal surface, the weakening effect will be poor with the increase of the concentration of the organic solvent; the temperature has a relatively obvious influence on the coffee ring effect, and the weakening of the coffee ring effect will be poor with the temperature being too high.

[0097] Figure 8 The digital photo of the paper with coating in Example 19 and Comparative Example 6 is shown in Figure 5. Figure 8 It can be seen that the method provided by the application is suitable for the paper surface, and can effectively weaken the coffee ring effect on the paper surface.

[0098] In summary, the method for inhibiting the coffee ring effect of the application is suitable for different solvents, mixed solutions with different concentrations, and different substrate surfaces, and has a wide application range. Compared with the normal drying method, the inverted drying method of the application can effectively inhibit the coffee ring effect.

[0099] The above only describes the preferred embodiments of the application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A method of suppressing the coffee ring effect, characterized in that, The method comprises the following steps: applying a liquid containing particles on a surface of a substrate to form a wet coating layer, inverting the wet coating layer to make it face downward, and drying the wet coating layer to obtain a coating layer that inhibits the coffee ring effect; the liquid containing particles comprises solid particles and a solvent; the solvent comprises water or a volatile organic solvent aqueous solution, wherein the volume fraction of the volatile organic solvent in the volatile organic solvent aqueous solution is less than or equal to 50%; the mass concentration of the solid particles in the liquid containing particles is 0.1-20%; the particle size of the solid particles is 0.01-10 μm; the solid particles are insoluble in water; and the maximum coating amount of the liquid containing particles is such that no liquid drips when the substrate is inverted; the drying temperature is 20-140 ℃.

2. The method of claim 1, wherein, the volatile organic solvent comprises at least one of a lower alcohol, an amide solvent, an ester solvent, and a ketone solvent.

3. The method of claim 2, wherein, the lower alcohol comprises methanol and / or ethanol; the amide solvent comprises N,N-dimethylformamide.

4. The method of claim 1, wherein, the solid particles comprise one or more of a metal element, an oxide, a metal salt, a polymer, a carbon material, boron nitride, and magnesium hydroxide.

5. The method of claim 4, wherein, the metal element comprises one or more of copper, iron, gold, cobalt, nickel, and silver; the oxide comprises a metal oxide and / or a non-metal oxide; the metal oxide comprises one or more of aluminum oxide, magnetite, magnesium oxide, and manganese oxide; and the non-metal oxide comprises silicon oxide; the metal salt comprises one or more of calcium carbonate and silver chloride; the polymer comprises one or more of a covalent organic framework material, an ionically porous organic polymer, cellulose, an epoxy resin, a phenol formaldehyde resin, and a polythiophene; the carbon material comprises one or more of carbon particles, carbon nanotubes, graphene, and graphite particles.

6. The method of claim 1, wherein, the substrate comprises a conductive material or an insulating material.

7. The method of claim 6, wherein, the conductive material comprises a metal electrode, a non-metal electrode, or conductive glass; the insulating material comprises non-conductive glass, ceramic, wood, plastic, or paper.

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