A method of interface assembly for preparing a Janus composite coating

Abstract

The application relates to the technical field of coating preparation, and particularly discloses a method for preparing a Janus composite coating through interface assembly, which comprises the following steps: directly putting a substrate into a nano-clay aqueous phase solution through a polymer oil phase solution, so that the surface of the substrate forms a Janus composite coating in the nano-clay aqueous phase solution; wherein the polymer oil phase solution contains a protonatable functional polymer; and the pH of the nano-clay aqueous phase solution is 4.5-7. The method effectively inhibits dewetting through interface assembly, prevents the occurrence of coating unevenness and cracking, and prepares a flat and thickness-controllable Janus composite coating by controlling various parameters, so the method has a great application prospect in the technical field of coating preparation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coating preparation, and particularly relates to a method for preparing a Janus composite coating through interface assembly BACKGROUND

[0002] Single material often can only play a limited role, in order to break this limitation, scientists try to use a variety of raw materials composite to produce new materials with higher performance, more functions. Janus material refers to the same material with clear structural partition and two different chemical components and chemical properties.

[0003] However, the existing method for preparing the Janus composite coating mostly adopts a form of step-by-step assembly, assembles two film materials with different performances together, or deposits and modifies another functional material on a film material. Such method has complicated preparation steps, and when the film material is prepared by solution processing, dewetting phenomenon is prone to occur, resulting in unevenness or even damage of the film material. And the interfacial force between the two film materials cannot be guaranteed, and the phenomenon of falling off and failure is prone to occur.

[0004] Or, part of the Janus film is prepared by interface assembly. Nanomaterials and polymers dispersed or dissolved in two solutions are assembled into a film on the interface by supramolecular interaction between the nanomaterials and the polymers. Due to the interaction between the assembly units, the stability of the composite coating is enhanced to a certain extent. However, due to the distance limitation of the supramolecular force, the film thickness is usually only nanoscale, and it is difficult to control, and it is not easy to meet the mechanical properties required in the subsequent use process.

[0005] Therefore, developing a new Janus composite coating preparation method to make up for the defects of the above-mentioned methods can effectively prepare more and better functional coatings, which has extremely important significance for the development of material science and application fields. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for preparing a flat Janus composite coating through interface assembly. In the present application, the substrate is introduced into the nanoclay aqueous phase through the polymer oil phase, so that the protonatable functional polymer is assembled with the nanoclay. That is, the surface of the substrate forms a Janus composite coating in the nanoclay aqueous solution. The method of the present application effectively suppresses dewetting by continuously introducing the oil phase into the water phase and assembling at the interface, preventing unevenness and cracking of the coating. And by controlling various parameters, a flat and thickness-controllable Janus composite coating is prepared, which has great application prospect in the field of coating preparation.

[0007] To achieve the above object, according to one aspect of the present application, there is provided a method for preparing a Janus composite coating through interfacial assembly, the method comprising:

[0008] directly immersing the substrate into the aqueous nanoclay solution through the polymer oil phase solution, so that the surface of the substrate forms a Janus composite coating in the aqueous nanoclay solution;

[0009] wherein the polymer oil phase solution comprises a protonatable functional polymer, the protonatable functional polymer being a polymer comprising a protonatable group; and the pH of the aqueous nanoclay solution is 4.5-7.

[0010] Preferably, the concentration of the nanoclay in the aqueous nanoclay solution is 25-50 mg / mL.

[0011] Preferably, the viscosity of the polymer oil phase solution is 2-2000 mPa·s.

[0012] Preferably, the directly immersing the substrate into the aqueous nanoclay solution through the polymer oil phase solution comprises:

[0013] pulling the substrate to be coated into the aqueous nanoclay solution from the polymer oil phase solution.

[0014] Preferably, the concentration of the protonatable functional polymer in the polymer oil phase solution is greater than 3*10 -6 mol / L; and the protonatable functional polymer is one of aminated polydimethylsiloxane, aminated polystyrene, polystyrene-poly(2-vinylpyridine) and polystyrene-poly(4-vinylpyridine).

[0015] Preferably, the polymer oil phase solution further comprises a solid polymer insoluble in the aqueous solvent; and the solid polymer insoluble in the aqueous solvent is one of polystyrene, polymethyl methacrylate and polycaprolactone.

[0016] Preferably, the nanoclay in the aqueous nanoclay solution is lithium bentonite or montmorillonite.

[0017] Preferably, the substrate to be coated is an organic solvent-resistant material, preferably a polyimide film.

[0018] Preferably, in step (2), the temperature when the substrate to be coated passes through the polymer oil phase solution is controlled to be 0-25 ℃.

[0019] In another aspect of the present invention, a Janus composite coating is prepared based on the preparation method of the first aspect of the present invention.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0021] (1) The substrate to be coated in this invention is directly introduced from an oil-phase solution containing a protonable functional polymer into an aqueous solution in which nano-clay is dispersed. Within a suitable pH range, the nano-clay and the protonable functional polymer can undergo supramolecular interactions, thereby assembling at the oil-water interface to form a Janus coating. In this invention, the rigid nano-clay accumulates in large quantities at the interface, forming a blockage, which effectively suppresses the dewetting phenomenon that is very easy to occur when preparing coatings through solution processing, ensuring the uniformity of the coating, improving the yield of the product, and showing great potential in the field of coating preparation.

[0022] (2) In addition, the present invention accelerates the assembly and stacking of nano-clay and protonable functional polymers at the oil-water interface by adjusting the concentration and viscosity of the oil-water phase solution. A large number of assemblies form a blockage at the interface in a short time, which can effectively suppress the occurrence of dewetting and ensure the uniformity of the coating. Finally, the preparation of the smooth Janus composite coating is completed by solvent evaporation.

[0023] (3) Further, the present invention uses traction to directly introduce the substrate to be coated into the aqueous solution of nano-clay through the polymer oil phase solution, so that the nano-clay is rapidly assembled at the interface with the assistance of the protonable functional polymer. The thickness of the coating is controlled by the traction speed, oil phase viscosity and surface tension. Different coating thicknesses can be obtained by adjusting different parameters. Attached Figure Description

[0024] Figure 1 This is an example of a preparation process in which a substrate after passing through a polymer oil phase is directly drawn into an aqueous phase of nano-clay.

[0025] Figure 2 The images shown are cross-sectional SEM images and surface AFM images of the coating sample exemplified in Embodiment 1 of the present invention. Figure 2 In the figure, 'a' and 'a' represent the polymer oil layer solution containing 6%... w / w PMMA and 1% v / v SEM images and surface AFM images of PDMS-2NH2 and coated samples prepared at a traction speed of 10 mm / s; Figure 2 In the figure, b and b' represent the polymer oil layer solution containing 6% w / w PMMA and 1%v / v SEM images and surface AFM images of PDMS and coated samples prepared at a traction speed of 6 mm / s; Figure 2 In the figure, c and c' represent the polymer oil layer solution containing 6% w / w PMMA and 10% v / v SEM images of the cross section and AFM images of the surface of the PDMS-coated sample prepared under the condition of traction speed of 6 mm / s;

[0026] Figure 3 This is a record of whether dewetting of the coating was suppressed by different aqueous phase ratios as illustrated in Example 2 of the present invention; wherein " "This indicates a uniform coating and good suppression of dewetting." "This indicates that the coating is cracked and dewetting has not been well suppressed."

[0027] Figure 4 This is the mass concentration-traction velocity phase diagram exemplified in Embodiment 3 of the present invention;

[0028] Figure 5 The figures show the curves of liquid layer thickness versus capillary number and the fitted curve in Example 3 of this invention; the inset shows the curve of function f(c) versus polymer oil phase solution concentration; the “Landau-Levich-Darjaguin” region (LLD region) indicates that the liquid layer thickness h in this region has a logarithmic linear relationship with the capillary number Ca, and the relationship is shown in the figure; the “Saturated region” indicates that the liquid layer thickness h in this region does not change with the capillary number Ca, indicating that the liquid layer thickness has entered the saturation region, where h = h* serves as the boundary between the two regions, and in this example, h* is approximately 120 μm;

[0029] Figure 6 The thinnest coating can be prepared by changing the PMMA content system as exemplified in Example 3 of this invention;

[0030] Figure 7 The thickest coating can be prepared by changing the PMMA content system as exemplified in Example 3 of this invention;

[0031] Figure 8 This is the mass concentration-traction velocity phase diagram exemplified in Embodiment 4 of the present invention;

[0032] Figure 9 These are comparative images of the coating samples morphology in Comparative Example 1 of this invention; wherein Figure 9 Groups i and ii in the figure represent the cross-sectional morphology and surface morphology of the coating samples containing protonable functional polymer groups, respectively.Figure 9 Groups iii and iv in the figure represent the cross-sectional and surface morphologies of the coated samples that do not contain protonable functional polymer groups.

[0033] Figure 10 This is a graph showing the change in surface tension over time between the nano-clay and the protonable functional polymer assembled at the interface in Example 5 of the present invention. Figure 10 Group i in the experiment consisted of pure chloroform and water with a pH of 9.0. Figure 10 Group ii in the experiment is the pure chloroform and nano-clay dispersion; Figure 10 Group iii in the experiment consisted of a chloroform solution containing a protonable functional polymer and water at pH 9.0. Figure 10 Group iv in the figure represents the experimental group containing a chloroform solution of a protonable functional polymer and an aqueous dispersion of nano-clay; the inset shows the droplet back-absorption morphology images corresponding to Group iv.

[0034] Figure 11 This is a graph showing the change in surface tension over time in Example 6 of the present invention; wherein... Figure 11 In the figure, 'a' represents the change in surface tension over time between aqueous dispersions of lithium saponin with different contents and protonable functional polymers. Figure 11 Figure b shows the droplet morphology at time 0s when the droplet retracts and wrinkles appear. The "1", "10", "25" and "50" in Figure b correspond to the conditions of 1 mg / mL, 10 mg / mL, 25 mg / mL and 50 mg / mL of lithium saponin in the clay aqueous solution.

[0035] The accompanying figures illustrate that the “dewetting region” indicates that the coating in this region has dewetting and a uniform coating cannot be prepared; the “anti-dewetting region” indicates that the interface assembly in this region triggers blockage under certain conditions, effectively suppressing the dewetting phenomenon of the coating and enabling the successful preparation of a uniform coating. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The diamino-modified polydimethylsiloxane (H2N-PDMS-NH2 or PDMS-2NH2), amino-modified polydimethylsiloxane (PDMS-NH2), toluene, chloroform, lithium saponite, montmorillonite, polystyrene (PS), polymethyl methacrylate (PMMA), and polycaprolactone (PCL) involved in the embodiments of the present invention were all purchased from the market.

[0038] In an embodiment of the present invention, the method for preparing a smooth Janus composite coating by interface assembly specifically includes the following steps:

[0039] Preparation of polymer oil phase solution: A protonable functional polymer is dissolved in an oil phase solvent, or both a protonable and non-protonable functional polymer are dissolved in an oil phase solvent. The viscosity of the polymer oil phase solution is controlled between 2 and 2000 mPa·s. Dissolution is accelerated using an ultrasonic cleaner. After the solution becomes clear and transparent, it is left to stand for at least 12 hours to obtain the polymer oil phase solution. The protonable functional polymer is a polymer containing protonable groups, such as amino or pyridyl groups.

[0040] In the embodiments, polymer oil phase solutions with different contents of protonable functional polymers are prepared by changing the content of the protonable functional polymer, and polymer oil phase solutions with different viscosities are prepared by changing the polymer content and temperature.

[0041] Among them, the content of protonable functional polymers in the polymer oil phase is greater than 3*10. -6 mol / L. For example, protonable functional polymers include amino-terminated polydimethylsiloxanes (H2N-PDMS-NH2 or PDMS-2NH2), amino-terminated polydimethylsiloxanes (PDMS-NH2), and amino-treated polystyrene (PS-NH2). Or one of polystyrene-poly(2-vinylpyridine) (PS-b-P2VP) and polystyrene-poly(4-vinylpyridine) (PS-b-P4VP).

[0042] The polymer oil phase solution also includes a solid polymer that is insoluble in water, such as polystyrene, polymethyl methacrylate, and polycaprolactone.

[0043] The oil phase solvent is any one of the organic solvents that are not miscible with water, such as toluene, carbon tetrachloride, chloroform, and dichloromethane.

[0044] Preparation of nanoclay dispersions: Nanoclay is a negatively charged two-dimensional nanoclay, such as lithium saponin or montmorillonite. A certain amount of lithium saponin is weighed and dispersed in ultrapure water using an ultrasonic cleaner until the dispersion becomes clear and transparent. After standing and aging for 1 hour, the pH of the nanoclay dispersion is adjusted to prepare a nanoclay dispersion with a concentration of 25-50 mg / mL. For example, the pH of the nanoclay dispersion can be adjusted using 0.1 M citric acid / sodium citrate buffer and 0.1 M sodium hydroxide aqueous solution.

[0045] In embodiments of the present invention, the pH of the nano-clay dispersion needs to ensure the protonation of the protonable functional polymer and the dispersibility of the nano-clay dispersion.

[0046] In an embodiment of the present invention, the substrate to be coated is directly introduced into the aqueous phase of nanoclay via a polymer oil phase, allowing the protonable functional polymer to assemble with the nanoclay. After the oil solvent in the polymer oil phase solution adhering to the substrate surface evaporates in the aqueous phase of nanoclay, a Janus composite coating is obtained. During the preparation process, the substrate remains in either an oil or aqueous phase without contact with air, ensuring that the protonable functional polymer assembles with the nanoclay in the aqueous phase continuously and within a short time after passing through the oil phase.

[0047] Furthermore, the uniformity and thickness of the Janus composite coating can be controlled by changing the ratio of the polymer oil phase and the nano-clay aqueous phase, as well as the rate at which the coating transitions from the oil phase to the aqueous phase.

[0048] The substrate can be a material resistant to organic solvents, such as a polyimide film.

[0049] In another embodiment of the invention, a connected quartz double-cell system is used, with one cell for containing a polymer oil phase solution and the other for containing a nano-clay aqueous phase solution. The two cells are connected by a joint that varies in size and shape depending on the substrate. When the two cells contain the two phase solutions, there is no clear boundary between the two phases at the joint, and they slightly merge, allowing the substrate to continuously transition from the oil phase into the aqueous phase. Figure 1 The diagram shows a preparation process in which the substrate, after passing through the polymer oil phase, is directly drawn into the aqueous phase of nanoclay.

[0050] Using a connected quartz double tank, the substrate to be coated is directly introduced into the nano-clay aqueous phase through a traction method, allowing the substrate to continuously transition directly from the polymer oil phase to the nano-clay aqueous phase, as detailed below:

[0051] Step 1: Use a connected quartz double tank. The left tank is used to place the polymer oil phase and the right tank is used to place the nano-clay aqueous phase. Ensure that the connection between the two phases is not isolated by the air phase, and ensure that the substrate can continuously transition directly from the polymer oil phase to the nano-clay aqueous phase.

[0052] Step 2: After immersing the planar substrate in the oil phase, the traction rate is controlled to pull it into the aqueous phase. At this time, the substrate drags the oil phase into the aqueous phase, and its surface is covered with a uniform and controllable oil layer. At the oil-water interface, there is an assembly of nano-clay and protonable functional polymer, thus obtaining the Janus composite coating.

[0053] The above describes how a large number of assemblies are deposited on the interface in a short period of time, causing blockage at the oil / water interface. This suppresses the spontaneous dewetting phenomenon that the planar liquid layer wants to reduce its surface energy, thus helping to obtain a smooth and uniform coating.

[0054] In an embodiment of the present invention, the Janus liquid layer is obtained using a traction substrate, specifically by controlling the substrate traction speed, oil phase viscosity, and oil-water interfacial tension. The theoretical thickness formula is as follows: Where A is a constant term and Ca is the capillary number. For traction speed, The viscosity of the polymer oil phase. The surface tension of oil and water.

[0055] The traction rate is controlled between 2 and 10 mm / s; the viscosity of the polymer oil phase is adjusted by adjusting the properties of the polymer or the temperature; and the surface tension is adjusted by changing the type of solution, the concentration of nano-clay and functional polymer, and the pH of the aqueous phase.

[0056] The following are specific embodiments, as detailed below:

[0057] Example 1

[0058] Prepare 6% w / w PMMA / 1% v / v PDMS-2NH2 / CHCl3 solution: At room temperature, 100 μL of PDMS-2NH2 was dissolved in 9.9 mL of chloroform, and then 0.9436 g of polymethyl methacrylate was added. The solution was then uniformly dissolved using an ultrasonic cleaner and allowed to stand for at least 12 hours to obtain 6% PDMS-2NH2 / CHCl3 solution. w / w PMMA / 1% v / v PDMS-2NH2 / CHCl3 solution, hereinafter referred to as 6w1v.

[0059] Prepare 6%w / w PMMA / 10% v / v PDMS-2NH2 / CHCl3 solution: At room temperature, 1000 μL of PDMS-2NH2 was dissolved in 9 mL of chloroform, and then 0.9159 g of polymethyl methacrylate was added. The solution was then dissolved uniformly using an ultrasonic cleaner and allowed to stand for at least 12 hours to obtain 6% PDMS-2NH2 / CHCl3 solution. w / w PMMA / 10% v / v PDMS-2NH2 / CHCl3 solution, hereinafter referred to as 6w10v.

[0060] To prepare a pH 5.5 / 50 mg / mL LAP aqueous dispersion: Weigh 500 mg of lithium bentonite (LAP) and disperse it in 10 mL of deionized water. Use an ultrasonic cleaner to uniformly disperse the dispersion until it is clear and transparent. After standing and aging for 1 hour, adjust the pH of the aqueous dispersion to 5.5 using 0.1 M citric acid / sodium citrate buffer and 0.1 M sodium hydroxide aqueous solution to obtain a pH 5.5 / 50 mg / mL LAP aqueous dispersion.

[0061] With the aqueous phase of the nano-clay kept constant, coating experiments were conducted by varying the oil phase parameters and the traction speed.

[0062] The oil phase parameters are the aforementioned 6w1v and 6w10v, wherein the content of the protonable functional polymer in 6w10v is ten times that in 6w1v.

[0063] The stationary aqueous dispersion was a 50 mg / mL LAP aqueous dispersion with a pH of 5.5. A 100 μm thick polyimide film resistant to organic solvent corrosion was selected as the substrate. Three coating experiments were conducted: (i) 6w1v with a traction speed of 10 mm / s; (ii) 6w1v with a traction speed of 6 mm / s; and (iii) 6w10v with a traction speed of 6 mm / s. The morphology was characterized using scanning electron microscopy (SEM), and the interfacial assembly behavior was characterized using atomic force microscopy (AFM).

[0064] like Figure 1As shown, Anti-Dewetting indicates successful suppression of dewetting, resulting in a uniform and complete coating, while Dewetting indicates that dewetting has occurred, leading to cracks in the prepared coating. The SEM image (top) clearly shows whether dewetting occurred during coating preparation, while the AFM image (bottom) shows the assembly of lithium saponite at the interface. The cobblestone-like AFM image indicates the presence of lithium saponite accumulation at the interface, demonstrating the successful preparation of the Janus composite coating. Furthermore, combining the two characterization images, it was found that the concentration of the protonable functional polymer and the substrate traction rate significantly affect coating uniformity and surface assembly behavior. Comparing the 6w1v / 10 mm / s and 6w1v / 6 mm / s groups, it was found that decreasing the velocity leads to coating inhomogeneity. There are two reasons for this. First, as the velocity decreases, the liquid layer thickness decreases, which in turn reduces the gravity of the liquid layer that counteracts surface tension, causing dewetting to occur earlier. Second, AFM images show that the particle size increases and the packing density decreases. This is because the liquid layer thickness also decreases with the reduced velocity. At the same concentration of protonable functional polymer, a lower velocity and thinner liquid layer result in a smaller amount of protonable functional polymer, while the interfacial area remains similar, leading to significant differences in the two sets of interfacial assembly behaviors. Two competing motions exist at the interface: the interfacial assembly between lithium bentonite and the protonable functional polymer, and the aggregation behavior of lithium bentonite itself. When the velocity decreases, the former motion is suppressed, resulting in more pronounced aggregation and an increase in particle size at the interface. Therefore, increasing the concentration of the protonable functional polymer, comparing the 6w1v / 6 mm / s and 6w10v / 6 mm / s groups, further suppresses dewetting, and the interfacial assembly becomes tighter with smaller particle sizes, consistent with theoretical observations.

[0065] Example 2:

[0066] Prepare different aqueous dispersions: Weigh out 100 mg, 100 mg, 250 mg, 250 mg, 500 mg, 500 mg, 1000 mg, and 1000 mg of lithium bentonite, respectively, and disperse them in 10 mL of deionized water. Use an ultrasonic cleaner to uniformly disperse the dispersions until they are clear and transparent. After standing and aging for 1 hour, obtain two bottles each of lithium bentonite aqueous dispersions with concentrations of 25 mg / mL, 50 mg / mL, 100 mg / mL, and 200 mg / mL. Then, adjust the pH of the aqueous dispersions to 5.5 and 7.0 using 0.1 M citrate / sodium citrate buffer and 0.1 M sodium hydroxide aqueous solution, respectively, to obtain pH 5.5 / 10 mg / mL, pH 7.0 / 10 mg / mL, pH 5.5 / 25 mg / mL, pH 7.0 / 25 mg / mL, pH 5.5 / 50 mg / mL, pH 7.0 / 50 mg / mL, and pH 7.0 / 50 mg / mL, respectively. Aqueous dispersion of LAP at 5.5 / 100 mg / mL and pH 7.0 / 100 mg / mL.

[0067] Preparation of the oil phase solution: At room temperature, dissolve 100 μL of PDMS-2NH2 in 9.9 mL of chloroform, then add 1.6426 g of polymethyl methacrylate (PMMA). Dissolve the solution uniformly using an ultrasonic cleaner and allow it to stand for at least 12 hours to obtain a 10% solution. w / w PMMA / 1% v / v PDMS-2NH2 / CHCl3 solution.

[0068] The oil phase solution and the prepared aqueous dispersion were mixed sequentially, and the traction speed was fixed at 2 mm / s. The uniformity of the resulting coating sample was recorded.

[0069] like Figure 2 As shown, This indicates a uniform coating and good suppression of dewetting. The coating showed signs of cracking, and dewetting was not effectively suppressed. At high pH, ​​the protonable functional polymers had low protonation levels, resulting in weak electrostatic interactions with the nanoclays. Slow interfacial assembly failed to effectively prevent interface blockage before cracking, ultimately leading to dewetting. Lowering the pH increased protonation and the average charge of the functional polymers, accelerating the interfacial assembly process with the nanoclays. Increasing the nanoclay concentration also promoted interfacial assembly. Therefore, at pH 5.5, dewetting was effectively suppressed when the concentration increased from 10 to 25 mg / mL and 50 mg / mL. However, further increasing the concentration to 100 mg / mL resulted in excessive nanoclay content, forming numerous aggregates in the aqueous phase and causing a sharp increase in the viscosity of the aqueous dispersion. This hindered the migration of nanoclays in the aqueous phase, slowing down their assembly with the functional polymers at the interface, thus failing to effectively suppress dewetting.

[0070] Example 3

[0071] The viscosity of the polymer oil phase was determined by preparing oil phase solutions with different polymer mass concentrations, as detailed below:

[0072] At room temperature, 100 μL of PDMS-2NH2 was dissolved in 9.9 mL of chloroform, and then 0.1493 g, 0.4572 g, 0.9436 g, 1.6426 g, and 2.6089 g of polymethyl methacrylate (PMMA) were added respectively. The solutions were then uniformly dissolved using an ultrasonic cleaner and allowed to stand for at least 12 hours to obtain 1% of the solution. w / w 3% w / w 6% w / w 10% w / w 15% w / w PMMA / 1% v / v The PDMS-2NH2 / CHCl3 solution has corresponding viscosities of 3.6 mPa·s, 9 mPa·s, 34 mPa·s, 204 mPa·s, and 1901 mPa·s.

[0073] Prepare an aqueous dispersion of LAP at pH 5.5 / 50 mg / mL: Prepare according to the method in Example 1.

[0074] Phase diagram preparation: The oil phase solutions of different mass concentrations were mixed with LAP aqueous dispersion at pH 5.5 / 50 mg / mL. Different traction speeds (2 mm / s, 6 mm / s, 10 mm / s) were used to divide the dewetting region / anti-dewetting region according to the coating morphology of each group of samples, and the phase diagram was prepared accordingly.

[0075] like Figure 4 As shown, a curve is used as the boundary line between the dewetting region and the anti-dewetting region. Simultaneously, the capillary number Ca(t) for each group is calculated using the formula. The phase diagrams were then differentiated by color. It was found that regions with high capillary numbers produced uniform and complete liquid layers, while regions with low capillary numbers were prone to liquid layer rupture. This is mainly because capillary number positively correlates with the thickness of the resulting liquid layer; therefore, high capillary number yields a thicker liquid layer, which promotes interfacial assembly of lithium saponite and mitigates liquid layer rupture (see analysis in Example 3). The creation of this phase diagram greatly facilitates subsequent manufacturing processes.

[0076] It should be noted that the calculation relationship between the thickness of the solid coating after evaporation and the thickness of the liquid layer before evaporation is based on Example 3.

[0077] As shown in Example 3, preparations were made with a mass fraction of 1%. w / w 3% w / w 6% w / w 10% w / w 15% w / w PMMA / 1% v / v Prepare a PDMS-2NH2 / CHCl3 solution and record its volume. .

[0078] Based on PMMA density Calculate the volume of PMMA , m represents the mass of PMMA.

[0079] Constructor function V represents the ratio of the thickness of the solid coating after evaporation to the thickness of the liquid layer before evaporation. soild V represents the volume of PMMA. liquid This indicates the volume of the polymer oil phase solution.

[0080] The cross-section of the coating was observed using SEM, and the thickness t of the solid coating was recorded. Then, the result was determined using the formula... Calculate the liquid layer thickness h.

[0081] By fitting the thickness h of each liquid layer to its capillary number Ca, a thickness control mechanism is obtained.

[0082] like Figure 4 As shown in the figure, the curve represents the change in liquid layer thickness with capillary number, and the inset shows the change in f(c) with PMMA mass fraction c. It can be seen that the curve contains two regions: the LLD region... and saturation region , respectively corresponding to Figure 4 The Landau-Levich-Derjaguin region and the Saturated region are defined, with h = h* serving as the boundary condition between the two regions. Within the LLD region, the liquid layer thickness h exhibits a good logarithmic linear relationship with the capillary number Ca. This facilitates subsequent control of the liquid layer thickness. Furthermore, during the measurement process, it can be observed that this method allows the system to achieve a minimum thickness of 300 nm. Figure 6 ) and a maximum thickness of 23 μm ( Figure 7 The coating has a minimum thickness that is far below the critical thickness of chloroform liquid layer in water (about 3251 μm), demonstrating the superiority of this method in preparing ultrathin uniform coatings.

[0083] Example 4

[0084] Based on Example 3, the ambient temperature was reduced from approximately 25°C to approximately 5°C; the operation of Example 3 was repeated to draw a phase diagram at a temperature of 5°C.

[0085] like Figure 8 As shown, a comparison was found. Figure 4 The boundary line shifts towards the low capillary number region. This is because low temperatures increase the viscosity of the liquid layer, thereby delaying dewetting and promoting coating uniformity.

[0086] Comparative Example 1

[0087] (1) Prepare an oil phase solution containing only polymer for coating: Weigh 1.648 g PMMA, dissolve it in 10 mL CHCl3, use an ultrasonic cleaner to dissolve it evenly, and let it stand for more than 12 hours.

[0088] (2) Prepare an oil phase solution containing a protonable functional polymer and a polymer for coating: Weigh 100 μL PDMS-2NH2 and 1.6426 g PMMA, dissolve them in 9.9 mL CHCl3, use an ultrasonic cleaner to dissolve them evenly, and let them stand for more than 12 hours.

[0089] (3) Preparation of aqueous dispersion for coating: Weigh 500 mg LAP and disperse it in 10 mL of deionized water. Use an ultrasonic cleaner to fully disperse it until it is clear and transparent, and let it stand for 1 hour to age. Use 0.1 M citric acid / sodium citrate buffer and 0.1 M sodium hydroxide aqueous solution to adjust the pH of the aqueous dispersion to 5.5, thereby obtaining a pH 5.5 / 50 mg / mL LAP aqueous dispersion.

[0090] Coating experiments were conducted with a traction speed of 2 mm / s using the solution systems in (1) & (3) and (2) & (3) respectively, and the resulting coatings were characterized by SEM.

[0091] like Figure 9 As shown, groups i and ii in the left column are coating samples containing protonable functional polymer groups, and groups iii and iv in the right column are coating samples without protonable functional polymer groups (control samples). Groups i and iii show the cross-sectional morphology of the two coating samples, and groups ii and iv show the surface morphology of the two coating samples.

[0092] The sample on the left, due to the presence of a protonable functional polymer in the oil phase solution, was able to ensure the efficient assembly of the originally non-interfacially active lithium saponite at the interface, forming a blockage that ultimately inhibited dewetting and resulted in a uniform and complete coating, which contrasted sharply with the damaged morphology on the right.

[0093] Example 5

[0094] Preparation of an oil-phase solution containing a protonable functional polymer: Dissolve 100 μL of PDMS-2NH2 in 9.9 mL of chloroform, accelerate dissolution using an ultrasonic cleaner, and allow the solution to stand overnight (at least 12 hours) after it becomes clear and transparent, thereby obtaining 1% v / v PDMS-2NH2 / CHCl3 solution.

[0095] Preparation of nano-clay dispersion: Weigh 10 mg of lithium saponin and disperse it in 10 mL of ultrapure water using an ultrasonic cleaner until the dispersion is clear and transparent. After standing and aging for 1 hour, adjust the pH of the aqueous dispersion to 9.0 using 0.1 M citric acid / sodium citrate buffer and 0.1 M sodium hydroxide aqueous solution.

[0096] The interfacial tensions of four groups were measured using an optical contact angle meter (OCA) via the pendant drop method: (i) pure chloroform and water at pH 9.0; (ii) pure chloroform and a dispersion of nano-clay; (iii) a chloroform solution containing a protonable functional polymer and water at pH 9.0; and (iv) a chloroform solution containing a protonable functional polymer and an aqueous dispersion of nano-clay. Furthermore, changes in droplet morphology were observed by performing a back-absorption operation on the droplets in group (iv) using OCA.

[0097] like Figure 10 The graph shows the evolution of surface tension over time for each group. The interfacial tension of the system of pure chloroform and water at pH 9.0 remained stable at around 33 mN / m, without a significant decrease. Changing the system to a pure chloroform and nano-clay aqueous dispersion resulted in almost no change in surface tension, indicating that nano-clay alone has no interfacial activity in the water / chloroform system. When the system consisted of a protonable functional polymer and water at pH 9.0, the surface tension decreased, and continued to decrease slowly over time. This indicates that the protonable functional polymer in the oil phase solution exhibits interfacial activity, spontaneously migrating from the oil phase to the interface and reducing the system's interfacial energy / interfacial tension. Furthermore, replacing the aqueous phase with a nano-clay aqueous dispersion again resulted in a further decrease in surface tension. This suggests that the presence of the protonable functional polymer (PDMS-2NH2) effectively attracts the nano-clay (LAP) in the aqueous phase, causing it to migrate to the interface. Ultimately, the two form an assembly at the interface, replacing the oil-water interfacial area and reducing the system's interfacial energy / interfacial tension.

[0098] At the same time, the droplets in group (iv) were drawn back, and the following was observed: Figure 10 As shown in the illustration, wrinkling occurs on the surface of the droplets. This anomalous interfacial behavior indicates that the assembly has formed a blockage at the interface, transforming the original liquid-like interfacial mechanical strength into a solid-like interfacial mechanical strength, which is crucial for subsequently inhibiting the dewetting of the liquid layer.

[0099] Example 6

[0100] Preparation of nano-clay dispersions of different concentrations: 0, 10, 100, 250, and 500 mg of lithium saponin were weighed and dispersed in 10 mL of ultrapure water. The dispersions were uniformly dispersed using an ultrasonic cleaner until the dispersions were clear and transparent. After standing and aging for 1 hour, the pH of the aqueous dispersions was adjusted to 7.0 using 0.1 M citric acid / sodium citrate buffer and 0.1 M sodium hydroxide aqueous solution.

[0101] Preparation of an oil-phase solution containing a protonable functional polymer: Dissolve 100 μL of PDMS-2NH2 in 9.9 mL of chloroform, accelerate dissolution using an ultrasonic cleaner, and allow the solution to stand overnight (at least 12 hours) after it becomes clear and transparent, thereby obtaining 1% v / v PDMS-2NH2 / CHCl3 solution.

[0102] The surface tension evolution curves of the prepared nano-clay dispersion and the oil phase solution of the protonable functional polymer were measured over time using the pendant drop method.

[0103] When droplets in each system are just formed, a back suction operation is performed to record the morphology of the droplet surface when wrinkles just appear.

[0104] like Figure 11 As shown in Figure a, when the dispersion concentration range is 0 ~ 25 mg / mL, the interfacial tension of the system decreases sequentially with increasing concentration, proving that the interfacial assembly kinetics accelerate with increasing concentration. When the concentration is further increased to 50 mg / mL, a slight increase in surface tension is observed. This is because nano-clay at excessively high concentrations is extremely prone to agglomeration in water. At this point, the size of individual agglomerates is too large, and the viscosity of the dispersion increases sharply, both of which slow down their migration rate to the interface and hinder the interfacial assembly kinetics.

[0105] at the same time, Figure 11 As shown in b, with increasing concentration, the ratio of the surface area at the point of wrinkling to the original droplet surface area, Sj / Si (as shown in Table 1 below), gradually increases. This means that although the assembly kinetics initially promotes and then delays the process, the ease with which the blockage phase transition is triggered becomes increasingly simple. For example, in the 50 mg / mL group, the droplet at time 0s only needs to reduce its surface area by about 9% to trigger the blockage phase transition.

[0106] Table 1 is based on Figure 11 Summary of data

[0107]

[0108] Among them, C LAP S represents the dispersion concentration of the aqueous dispersion. j / S i The surface area S represents the area of ​​the droplet when wrinkles appear during the backflow process. jamming With the initial surface area S of the droplet initial The ratio of IFT to IFT, to some extent, represents the ease with which a blocking phase transition can occur at the interface within this system. final This represents the interfacial tension value at the final stable moment.

[0109] In summary, this invention utilizes the electrostatic interaction between protonable functional polymers and nanoclay to assist the previously non-interfacially active nanoclay in successfully assembling at the interface, thereby forming a Janus composite coating. The rapid assembly and blockage of the protonable functional polymers and nanoclay at the interface successfully suppresses dewetting, a phenomenon that easily occurs during solution processing for planar coatings, ensuring the uniformity and integrity of the resulting coating. The innovatively designed coating process allows for controllable coating thickness, which is of great importance in the field of coating preparation technology.

[0110] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing Janus composite coatings via interfacial assembly, characterized in that, The method includes: A planar substrate is directly introduced into a nano-clay aqueous solution via a polymer oil phase solution, resulting in a uniform and controllable thickness oil layer covering the surface of the planar substrate. Assemblies of nano-clay and protonable functional polymers exist at the interface, causing blockage at the oil / water interface. This suppresses the spontaneous dewetting phenomenon caused by the planar liquid layer's desire to reduce surface energy, thereby forming a Janus composite coating in the nano-clay aqueous solution. The traction velocity of the planar substrate as it directly enters the nano-clay aqueous solution from the polymer oil phase solution is 2 ~ 10 mm / s. The polymer oil phase solution has a viscosity of 2 to 2000 mPa·s, and contains a protonable functional polymer, which is a polymer containing a protonable group; the nano-clay is lithium saponite or montmorillonite, and the concentration of nano-clay in the aqueous nano-clay solution is 25 to 50 mg / mL, with a pH of 4.5 to 7.

2. The method for preparing Janus composite coatings via interface assembly according to claim 1, characterized in that, The process of directly introducing a planar substrate into a nano-clay aqueous solution via a polymer oil phase solution includes: The planar substrate is drawn from the polymer oil phase solution into the nano-clay aqueous phase solution.

3. The method for preparing Janus composite coatings via interface assembly according to claim 1, characterized in that, The concentration of the protonable functional polymer in the polymer oil phase solution is greater than 3*10. -6 mol / L; the protonable functional polymer is one of aminated polydimethylsiloxane, aminated polystyrene, polystyrene-poly(2-vinylpyridine), and polystyrene-poly(4-vinylpyridine).

4. The method for preparing Janus composite coatings via interface assembly according to claim 1, characterized in that, The polymer oil phase solution further includes a solid polymer that is insoluble in water; the solid polymer that is insoluble in water is one of polystyrene, polymethyl methacrylate, and polycaprolactone.

5. The method for preparing Janus composite coatings via interface assembly according to claim 1, characterized in that, The planar substrate is made of an organic solvent resistant material.

6. The method for preparing Janus composite coatings via interface assembly according to claim 5, characterized in that, The planar substrate is a polyimide film.

7. The method for preparing Janus composite coatings via interfacial assembly according to claim 1, characterized in that, In step (2), the temperature of the planar substrate when passing through the polymer oil phase solution is controlled to be 0 ~ 25 ℃.

8. The Janus composite coating obtained by the method according to any one of claims 1-7.

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