A PDA / ODT-ODTMS composite coating and its preparation method

Abstract

This invention provides a PDA / ODT-ODTMS composite coating and its preparation method, relating to the field of metal surface protection technology. The coating comprises, from the inside out, a polydopamine intermediate layer and a co-deposited functional layer of n-octadecyl mercaptan / octadecyltrimethoxysilane. The preparation method involves first electrodepositing a PDA intermediate layer on the substrate surface, then immersing it in an aqueous micelle deposition solution composed of n-octadecyl mercaptan, octadecyltrimethoxysilane, and a surfactant, and forming the composite functional layer through isothermal chemical deposition. This invention, through molecular-level co-deposition of ODT and ODTMS combined with an aqueous micelle process, constructs a firmly adhered, dense, and highly hydrophobic protective barrier on the metal surface, significantly improving the long-term corrosion resistance and stability of the coating, while also making the preparation process safer and more environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of metal material surface protection technology, specifically relating to a PDA / ODT-ODTMS composite coating and its preparation method. Background Technology

[0002] Metallic materials, especially copper and its alloys, are widely used in pipelines, heat exchangers, and critical equipment in energy, chemical, power, and marine engineering fields due to their excellent electrical, thermal, and mechanical properties. However, when these devices are used for extended periods in humid or corrosive media containing chloride ions, severe electrochemical corrosion occurs, leading to material failure, performance degradation, and even safety accidents such as leaks, resulting in significant economic losses and resource waste.

[0003] To extend the service life of metal equipment, surface protective coating technology is considered one of the most economical and effective strategies. Currently, commonly used industrial protective technologies mainly include chromate passivation, phosphating, organic coatings, and electroplating or electroless plating of metal layers. However, these traditional technologies all have significant shortcomings: chromates have been strictly restricted due to their high toxicity and environmental hazards; phosphating films are porous, have limited protective capabilities, and involve heavy metals in the process; organic coatings often lack adhesion and long-term durability, and are prone to peeling; while single metal coatings are prone to galvanic corrosion or localized pitting corrosion in complex corrosive environments.

[0004] In recent years, researchers have been dedicated to developing novel, environmentally friendly, and highly efficient composite protective coatings. An ideal coating needs to possess strong adhesion to the substrate, a dense and stable structure, and excellent physical shielding and chemical inertness against corrosive media. However, existing technologies often struggle to simultaneously meet these requirements. Some composite coatings prepared through simple physical mixing or stepwise dip coating still require improvement in the bonding strength between components, coating uniformity, and long-term stability. Furthermore, process controllability, reproducibility, and suitability for large-scale production are key challenges in practical applications.

[0005] Therefore, developing a novel composite coating technology that is process-controllable, can form a strong bond with the metal substrate, and can build a long-term stable and dense barrier is an urgent practical need for solving the problem of long-term corrosion protection of key metal components such as copper alloys. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing a PDA / ODT-ODTMS composite coating and its preparation method, thereby solving problems such as insufficient coating adhesion, poor density, complex processes, or poor stability in the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a PDA / ODT-ODTMS composite coating, which is disposed on the surface of a metal substrate and comprises, from the inside to the outside, a polydopamine (PDA) intermediate layer and a co-deposited functional layer of n-octadecyl mercaptan / octadecyltrimethoxysilane (ODT-ODTMS).

[0008] Furthermore, the PDA intermediate layer is formed in situ by electrodeposition on the surface of the metal substrate; the ODT-ODTMS co-deposited functional layer is constructed on the PDA intermediate layer by chemical deposition.

[0009] Furthermore, in the ODT-ODTMS co-deposited functional layer, the mass ratio of ODT to ODTMS is 1:0.2 to 1:1.

[0010] The co-deposition of ODT and ODTMS forms a composite functional layer with a unique structure. ODT forms covalent bonds with the active sites of the PDA layer through its thiol groups, constituting the backbone and hydrophobic base of the functional layer. The silanol groups generated after the hydrolysis of ODTMS bond with the polar functional groups of PDA, enhancing interfacial bonding; on the other hand, they form a siloxane network through intermolecular condensation. This network permeates the hydrophobic matrix composed of ODT molecules, significantly improving the cohesive strength and density of the film and effectively reducing microscopic defects. This structure gives the coating excellent adhesion, lower porosity, and stronger barrier properties against corrosive media, thus achieving long-lasting corrosion protection.

[0011] The second aspect of this invention provides a method for preparing the above-mentioned PDA / ODT-ODTMS composite coating, comprising the following steps: (1) Grind, polish, clean and dry the surface of the metal substrate to obtain a clean surface; (2) Dissolve dopamine hydrochloride in deionized water to prepare DA electrodeposition solution; disperse the mixed oil phase of n-octadecyl mercaptan (ODT) and octadecyltrimethoxysilane (ODTMS) in deionized water in the presence of surfactant to form an aqueous micelle deposition solution. (3) Using the metal substrate treated in step (1) as the cathode, electrodeposit it in the DA electrodeposition solution to form a PDA intermediate layer on the substrate surface; (4) The substrate covered with the PDA intermediate layer is immersed in an aqueous micelle deposition solution for chemical deposition, taken out, rinsed, and heat-treated to form an ODT-ODTMS co-deposited functional layer on the surface of the PDA intermediate layer, thus obtaining a composite coating.

[0012] Further, the concentration of dopamine hydrochloride in the DA electrodeposition solution in step (2) is 0.4 ~ 1.6 mg / mL.

[0013] Furthermore, the electrodeposition process in step (3) is carried out at 45±2℃, the DC voltage of the electrodeposition is 20~50 V, and the deposition time is 5~10 minutes.

[0014] Further, the total mass of ODT and ODTMS in step (2) is 0.1~0.5 wt% in the aqueous micelle deposition solution.

[0015] Further, in step (2), the surfactant is polyoxyethylene octylphenol ether-10, and its concentration in deionized water is 0.5 ~ 2.0 wt%.

[0016] Furthermore, the chemical deposition process described in step (4) is carried out at 40±2℃ for 4 to 8 hours.

[0017] Further, the heat treatment in step (4) is to heat treat at 79 ~ 90 ℃ for 20 ~ 40 minutes.

[0018] The preparation method of this invention uses aqueous micelle deposition instead of the traditional ODT ethanol solution. It utilizes surfactants to encapsulate and uniformly disperse the hydrophobic ODT and ODTMS in water, eliminating the safety hazards and costs associated with using large amounts of flammable organic solvents. Furthermore, the aqueous environment directly provides the necessary conditions for the hydrolysis reaction of ODTMS. The micelle system enables more uniform transport and adsorption of the reactants on the hydrophilic PDA surface, which is beneficial for forming a uniform film.

[0019] The stepwise electrodeposition and chemical deposition processes, along with precisely controlled temperature parameters, ensured the orderly formation of each layer. Electrodeposition of the PDA layer at specific voltages and temperatures rapidly formed a strongly bonded and fully covered sublayer. Subsequently, the chemical deposition of the functional layers was carried out under mild conditions of 40°C. This temperature maintained micellar stability while providing sufficient molecular kinetic energy to promote the reaction and adsorption of ODT and ODTMS at the interface, while avoiding premature over-condensation of ODTMS due to excessively high temperatures.

[0020] Furthermore, the heat treatment step drives the hydrolysis-condensation reaction of ODTMS, promoting the full cross-linking and curing of the siloxane network. This process effectively "locks in" ODT molecules and eliminates intramembrane stress, transforming the functional layer from its initial state, which mainly relies on physical adsorption, into a final protective layer with high cohesive strength and a stable chemical structure.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. Regarding the coating structure, a unique composite functional layer was constructed through molecular-level co-deposition of n-octadecyl mercaptan (ODT) and octadecyltrimethoxysilane (ODTMS). ODT molecules, acting as the main chain, are firmly anchored to the PDA intermediate layer via covalent bonds, providing basic hydrophobicity. Meanwhile, the three-dimensional siloxane network formed by the hydrolysis and condensation of ODT is interwoven within the hydrophobic ODT matrix, significantly enhancing the cohesive strength and density of the film. This synergistic structure effectively reduces microscopic defects in the coating and lowers the penetration rate of water, oxygen, and corrosive ions, thereby achieving a fundamental improvement in the long-term anti-corrosion performance of the coating. Potentiodynamic polarization curve testing shows that the corrosion inhibition efficiency of this composite coating can reach up to 97.6%, significantly superior to single-component coatings or traditional processes.

[0022] 2. In terms of the preparation process, an innovative aqueous micelle deposition technique is used to replace the traditional ODT organic solvent system. The surfactant-formed micelles effectively disperse the hydrophobic reactive monomers in water, eliminating not only the safety risks and costs associated with using large amounts of flammable organic solvents, but also making the preparation process more environmentally friendly. Simultaneously, the aqueous environment provides the necessary conditions for the hydrolysis reaction of ODTMS, which is conducive to the formation of the siloxane network. Combined with subsequent heat treatment steps, this promotes the full cross-linking and curing of the siloxane network, ultimately resulting in a structurally stable and strongly adherent composite coating. Attached Figure Description

[0023] Figure 1 SEM images of bare copper substrates after immersion in a 3.5 wt% sodium chloride solution for 5 days; Figure 2 SEM image of the coating prepared in Example 1 after immersion in 3.5 wt% sodium chloride solution for 5 days; Figure 3 SEM image of the coating prepared in Example 2 after immersion in 3.5 wt% sodium chloride solution for 5 days; Figure 4 SEM image of the coating prepared in Example 3 after immersion in 3.5 wt% sodium chloride solution for 5 days; Figure 5 Potentiodynamic polarization curves measured on bare copper substrates and in Examples 1-3 in a 3.5 wt% sodium chloride environment; Figure 6 The potentiodynamic polarization curves for comparative examples 1-6 were measured in a 3.5 wt% sodium chloride environment. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In addition, it is worth noting that the raw materials involved in the present invention are all commercially available products unless otherwise specified.

[0025] Example 1 This embodiment provides a PDA / ODT-ODTMS composite coating, the preparation method of which includes the following steps: (1) Take a T2 copper plate with dimensions of 50 mm × 25 mm × 2 mm as the substrate. Use 600#, 1200# and 2000# metallographic sandpaper to polish its surface step by step until the surface scratches are uniform and fine. Then, apply a small amount of white paraffin wax as polishing paste on a polishing machine equipped with white polishing cloth, and mechanically polish the polished copper plate until the surface is mirror bright. Immerse the polished copper plate in a beaker containing paraxylene and ultrasonically clean it at a frequency of 40 kHz for 10 minutes to completely remove the paraffin wax adhering to the surface. Afterwards, rinse the surface of the copper plate with deionized water and anhydrous ethanol in sequence, and finally blow it dry with clean nitrogen gas and place it in a desiccator for later use.

[0026] (2) Preparation of DA electrodeposition solution: Accurately weigh 60 mg of dopamine hydrochloride, place it in a 500 mL beaker, add 50 mL of deionized water, stir for 15 minutes to obtain a homogeneous solution with a concentration of 1.2 mg / mL, and transfer the DA electrodeposition solution to a constant temperature water bath at 45℃ for preheating.

[0027] Preparation of aqueous ODT-ODTMS micelle deposition solution: Accurately measure 0.126 g of n-octadecyl mercaptan (ODT, analytical grade) and 0.066 g of octadecyltrimethoxysilane (ODTMS, analytical grade), and mix them to obtain a mixed oil phase of ODT and ODTMS. Measure 100 mL of deionized water and add 1.00 g of polyoxyethylene octylphenol ether-10 (Triton X-100, chemically pure), stirring until completely dissolved to obtain a 1.0 wt% surfactant aqueous solution. While stirring, slowly add the mixed oil phase dropwise to the surfactant aqueous solution. After the addition is complete, continue stirring for 30 minutes to obtain the aqueous micelle deposition solution. Transfer the deposition solution to a 40℃ constant temperature water bath for later use.

[0028] (3) Using the T2 copper plate processed in step (1) as the cathode and the high-purity nickel plate as the anode, immerse the plate in the DA electrodeposition solution. Place the entire device in a 45°C constant temperature water bath, connect a DC regulated power supply, set the voltage to 40 V, and turn on the power for electrodeposition for 6 minutes. After deposition, remove the copper plate, rinse the surface with deionized water, and then place it in a 60°C forced-air drying oven to dry for 10 minutes. At this time, a uniform PDA intermediate layer is formed on the surface of the copper plate.

[0029] (4) Completely immerse the copper plate coated with the PDA intermediate layer in the aqueous micelle deposition solution. Maintain the system in a constant temperature water bath at 40℃ and let it stand for 6 hours. After immersion, remove the copper plate, rinse it with deionized water, and then place the copper plate in an 80℃ forced-air drying oven for heat treatment for 30 minutes. After heat treatment, allow it to cool naturally to room temperature to obtain the PDA / ODT-ODTMS composite coating.

[0030] Example 2 This embodiment provides a PDA / ODT-ODTMS composite coating, which differs from Example 1 in that the concentration of the DA electrodeposition solution in step (2) is 0.5 mg / mL.

[0031] Example 3 This embodiment provides a PDA / ODT-ODTMS composite coating, which differs from Embodiment 1 in that: in step (2), when preparing the aqueous ODT-ODTMS micelle deposition solution, the mass of n-octadecyl mercaptan is 0.23g and the mass of octadecyltrimethoxysilane is 0.22g.

[0032] Comparative Example 1 This comparative example provides a PDA / DDT-ODTMS composite coating, which differs from Example 1 in that n-octadecyl mercaptan is replaced with n-dodecyl mercaptan.

[0033] Comparative Example 2 This comparative example provides a PDA / ODT composite coating, which differs from Example 1 in that the aqueous ODT-ODTMS micelle deposition solution prepared in step (2) is replaced with: 0.126 g of n-octadecyl mercaptan is accurately measured and added to 100 mL of anhydrous ethanol. Subsequently, 75 μL of triethylamine is added as a reaction catalyst. The mixture is placed on a magnetic stirrer and stirred at room temperature for 30 minutes until a clear and homogeneous ODT ethanol deposition solution is obtained. The deposition solution is transferred to a constant temperature water bath at 40°C for equilibration.

[0034] Comparative Example 3 This comparative example provides a PDA / ODTMS composite coating, which differs from Example 1 in that n-octadecyl mercaptan is not added in step (2).

[0035] Comparative Example 4 This comparative example provides a PDA / ODT-ODTMS composite coating, which differs from Example 1 in that: in step (2), when preparing the aqueous ODT-ODTMS micelle deposition solution, the mass of n-octadecyl mercaptan is 0.13g and the mass of octadecyltrimethoxysilane is 0.32g.

[0036] Comparative Example 5 This comparative example provides a PDA / ODT-ODTMS composite coating, which differs from Example 1 in that the electrodeposition temperature in step (3) is 35°C.

[0037] Comparative Example 6 This comparative example provides a PDA / ODT-ODTMS composite coating, which differs from Example 1 in that the deposition temperature in step (4) is 55°C.

[0038] Performance testing Test samples: Coating samples prepared in Examples 1-3 and Comparative Examples 1-6.

[0039] Test method: 1. Observation of Coating Morphology and Durability: The coating samples from Examples 1-3 and the bare copper substrate were completely immersed in a 3.5 wt% sodium chloride solution and statically soaked at room temperature for 5 days. After soaking, the samples were removed, gently rinsed with deionized water, and dried. The surface of the soaked samples was then sputter-coated with gold, and their surface morphology was observed under SEM. Figure 1-4 As shown.

[0040] Figure 1 The image shows the surface morphology of a bare copper substrate after being soaked in salt water for 5 days. As can be seen from the image, the surface is no longer smooth and flat, but has a large number of bumps and pits, which proves that the bare copper substrate has undergone severe corrosion in the salt water environment.

[0041] Figure 2-4 The figures show the surface morphology of the coating samples from Examples 1-3 after immersion in salt water for 5 days. As can be seen from the figures, the composite coating systems in the three examples all remain flat, with no signs of severe corrosion on the surface, proving that the prepared composite coating systems all have highly efficient corrosion resistance.

[0042] 2. Potentiodynamic polarization curve testing: The test was conducted on an electrochemical workstation using a three-electrode system: the sample under test as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. The corrosive medium was a 3.5 wt% sodium chloride solution. Before testing, the sample was immersed in the medium until the open-circuit potential stabilized. Then, the potential-current density curve was recorded from the relative open-circuit potential of -0.5 V to 0.0 V at a scan rate of 5 mV / s. The curve was analyzed using the Tafel extrapolation method to obtain the self-corrosion current density and self-corrosion potential of the sample, and its corrosion inhibition efficiency relative to the bare copper substrate was calculated to quantitatively compare the protective performance of different coatings.

[0043] The potentiodynamic polarization curves of the copper substrate and Examples 1-3 are shown below. Figure 5 As shown, the potentiodynamic polarization curves of Comparative Examples 1-6 are as follows: Figure 6 As shown.

[0044] The corrosion inhibition efficiency is shown in Table 1.

[0045] Table 1 Corrosion Inhibition Efficiency The results of potentiodynamic polarization curve tests quantitatively revealed the differences in corrosion resistance of different coating systems. For example... Figure 5 As shown, the polarization curves of all the sample examples shifted significantly downwards compared to the bare copper substrate, indicating a significant reduction in corrosion current density, which proves that the solution of the present invention can provide excellent and stable protection.

[0046] Comparative Example 1 showed an efficiency drop to 83.3%, demonstrating the crucial role of the octadecyl long chain in forming a dense hydrophobic layer. Comparative Example 2 achieved an efficiency of 89.0%, demonstrating the performance gain resulting from the synergistic effect of "ODTMS co-deposition" and "aqueous micellar process." Comparative Example 3 experienced a sharp drop in efficiency to 40.7%, indicating that an effective protective layer could not be formed without ODT as the primary reaction anchor point. Comparative Example 4 had an efficiency of only 78.6%, demonstrating that coating performance significantly deteriorates when the ODT proportion exceeds the preferred range of this invention. Comparative Examples 5 and 6 also showed reduced efficiency due to deviations from the preferred process temperature, highlighting the importance of optimizing process parameters.

[0047] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A PDA / ODT-ODTMS composite coating, wherein the composite coating is disposed on the surface of a metal substrate and comprises, from the inside out: A functional layer is co-deposited with a polydopamine (PDA) interlayer and n-octadecyl mercaptan / octadecyltrimethoxysilane (ODT-ODTMS).

2. The PDA / ODT-ODTMS composite coating according to claim 1, characterized in that: The PDA intermediate layer is formed by in-situ polymerization on the surface of the metal substrate through an electrodeposition process; the ODT-ODTMS co-deposited functional layer is constructed on the PDA intermediate layer through a chemical deposition process.

3. The PDA / ODT-ODTMS composite coating according to claim 1, characterized in that: In the ODT-ODTMS co-deposited functional layer, the mass ratio of ODT to ODTMS is 1:0.2 to 1:

1.

4. The method for preparing the PDA / ODT-ODTMS composite coating according to any one of claims 1-3, comprising the following steps: (1) Grind, polish, clean and dry the surface of the metal substrate to obtain a clean surface; (2) Dissolve dopamine hydrochloride in deionized water to prepare DA electrodeposition solution; disperse the mixed oil phase of n-octadecyl mercaptan (ODT) and octadecyltrimethoxysilane (ODTMS) in deionized water in the presence of surfactant to form an aqueous micelle deposition solution. (3) Using the metal substrate treated in step (1) as the cathode, electrodeposit it in the DA electrodeposition solution to form a PDA intermediate layer on the substrate surface; (4) The substrate covered with the PDA intermediate layer is immersed in an aqueous micelle deposition solution for chemical deposition, taken out, rinsed, and heat-treated to form an ODT-ODTMS co-deposited functional layer on the surface of the PDA intermediate layer, thus obtaining a composite coating.

5. The preparation method according to claim 4, characterized in that: The concentration of dopamine hydrochloride in the DA electrodeposition solution in step (2) is 0.4 ~ 1.6 mg / mL.

6. The preparation method according to claim 4, characterized in that: The electrodeposition process in step (3) is carried out at 45±2℃, the DC voltage of the electrodeposition is 20~50 V, and the deposition time is 5~10 minutes.

7. The preparation method according to claim 4, characterized in that: The total mass of ODT and ODTMS in step (2) is 0.1 ~ 0.5 wt% in the aqueous micelle deposition solution.

8. The preparation method according to claim 4, characterized in that: In step (2), the surfactant is polyoxyethylene octylphenol ether-10, and its concentration in deionized water is 0.5 ~ 2.0 wt%.

9. The preparation method according to claim 4, characterized in that: The chemical deposition process described in step (4) is carried out at 40±2℃ for 4 to 8 hours.

10. The preparation method according to claim 4, characterized in that: The heat treatment in step (4) is to heat treat at 79 ~ 90 ℃ for 20 ~ 40 minutes.

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