A method for preparing a hydrophobic thin film by in-situ assembly of dopamine

Abstract

The present invention relates to a method for preparing a hydrophobic thin film by in-situ assembly of dopamine. First, under weakly alkaline conditions, dopamine undergoes an oxidation-crosslinking reaction and self-polymerizes into a polydopamine thin film that adheres to the surface of the substrate. The surface of the substrate is washed and dried. Then, it is placed in an anhydrous acylation reagent solution to undergo an esterification reaction and an amidation reaction to generate a hydrophobic polymer, and a hydrophobic thin film is obtained on the substrate. The present invention uses an acylation reagent to undergo a secondary esterification reaction and an amidation reaction with the polydopamine thin film deposited on the substrate to generate a hydrophobic thin film with high adhesion. The acyl group is grafted in-situ at -OH and NH2 on the hydrophobic thin film, modifying the hydrophilic property to a hydrophobic property. This method is simple, fast, and green, and has broad application prospects in various fields such as architectural coatings, biomedicine, purification and environmental protection, and functional textiles.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials and relates to a method for preparing a hydrophobic film by in-situ assembly of dopamine. Background Art

[0002] The catechol derivative 3,4-dihydroxyphenylalanine (dopamine) of L-3,4-dihydroxyphenylalanine, as a biological neurotransmitter, contains both catechol and amino functional groups. This structure and composition are similar to the key components of adhesion performance in adhesion proteins, and can establish covalent-non-covalent interactions with the material surface, thus realizing the super adhesion behavior of dopamine molecules to the material surface. Under weakly alkaline conditions, the catechol groups in dopamine can undergo oxidation-crosslinking reactions under the action of dissolved oxygen and self-polymerize into a composite polydopamine film that adheres to the surface of any substrate such as polymers, metals, ceramics, glass, wood, etc., and there are no restrictions on the shape and size of the material, achieving surface modification. At the same time, the active groups such as phenolic hydroxyl groups and amino groups contained in polydopamine can be used as a secondary reaction platform for further surface modification, grafting small molecules, metal ions, etc. to prepare a variety of highly adhesive functional layers. Zhou et al. (Organic Electronics, 2019, 75, 105408) demonstrated that the adhesion between a metal silver grid and a flexible PET substrate can be improved by covering a layer of polydopamine on the flexible PET substrate before preparing the metal silver grid, thereby improving the mechanical stability of the silver grid during bending.

[0003] A hydrophobic surface refers to a surface with an apparent contact angle with water greater than 90°, and a superhydrophobic surface when the apparent contact angle is greater than 150°. For hydrophilic polydopamine, the method for preparing a hydrophobic surface is to modify a low surface energy substance or graft a molecule with a hydrophobic group on the polydopamine surface with a certain roughness. Chinese Patent (CN 112029409 A) reported a polydopamine concrete hydrophobic coating material and its preparation method. Specifically, it is obtained by polymerizing dopamine hydrochloride and a thiol-containing small molecule compound dissolved in a mixed solution of Tris-HCl buffer solution and ethanol. Chinese Patent (CN110004722 A) reported a preparation method for a hydrophobic cotton fabric by copolymerizing dopamine and a hydrophobic compound. Specifically, it uses laccase to catalyze the copolymerization of dopamine and 2,2-bis(3-amino, 4-hydroxyphenyl)hexafluoropropane to generate a hydrophobic copolymer with an adhesive effect and deposit it on the surface of the cotton fabric.

[0004] Object of the Invention

[0005] The object of the present invention is to provide a method for preparing a hydrophobic thin film by in-situ assembly of dopamine. In an aqueous system, dopamine undergoes oxidative self-polymerization on the surface of a substrate to form polydopamine; subsequently, the modified substrate undergoes a secondary reaction with an acid anhydride (carboxylic acid, acyl chloride, etc.) to in-situ assemble into a highly adhesive hydrophobic thin film. This method is simple, rapid, and green, and has broad application prospects in various fields such as architectural coatings, biomedicine, purification and environmental protection, and functional textiles.

[0006] A method for preparing a hydrophobic thin film by in-situ assembly of dopamine, comprising the following steps:

[0007] (1) Provide a substrate;

[0008] (2) Under weakly alkaline conditions, dopamine undergoes an oxidation-crosslinking reaction and self-polymerizes into a polydopamine thin film that adheres to the surface of the substrate. Wash the surface of the substrate and dry it;

[0009] (3) Place the substrate with the polydopamine thin film adhered thereon into an anhydrous acylation reagent solution to undergo an esterification reaction and an amidation reaction to generate a hydrophobic polymer, and obtain a hydrophobic thin film on the substrate. The acylation reagent is an organic carboxylic acid, an organic acid anhydride, or an organic acyl chloride.

[0010] The organic carboxylic acid has 1-9 carbon atoms, the organic acid anhydride has 2n carbon atoms, where n is a positive integer from 2 to 8, and the organic acyl chloride has 2-12 carbon atoms.

[0011] The acylation reagent is an organic acid anhydride.

[0012] The organic acid anhydride is propionic anhydride.

[0013] The weakly alkaline condition is that the pH of the solution is 8.0-8.5.

[0014] The method of step (2): Add dopamine hydrochloride to a tris(hydroxymethyl)aminomethane hydrochloride buffer solution and stir to mix it thoroughly. Then pour all the solution into a petri dish containing a clean and dry substrate. After standing and soaking at room temperature for 24 h or ultrasonic treatment for 30 min, dopamine undergoes oxidative self-polymerization in a weakly alkaline environment and forms a dense polydopamine thin film on the surface of the substrate.

[0015] The substrate is a PET substrate or a PDMS substrate.

[0016] The hydrophobic thin film prepared by the above method.

[0017] Application of the above hydrophobic thin film in waterproof materials.

[0018] The waterproof materials are architectural coatings, biomedicine, purification and environmental protection, and functional textiles.

[0019] The present invention is a class of hydrophobic materials developed on the basis of the existing polydopamine film. Dopamine can form a polydopamine film on various substrates. Due to the presence of multiple -OH or NH2 on the surface layer of the polydopamine film, the polydopamine film has good hydrophilic properties. In the present invention, an acylating reagent is used to carry out a secondary esterification reaction and an amidation reaction with the polydopamine film deposited on the substrate to generate a hydrophobic film with high adhesion. The hydrophobic film has acyl groups grafted in situ at -OH and NH2, modifying the hydrophilic property to a hydrophobic property.

[0020] Comparing the infrared characteristic peaks of the polydopamine film and the hydrophobic film, it is found that the characteristic peaks of the polydopamine film at 1510 cm -1 , 3435 cm -1 , 3500 cm -1 -3543 cm -1 disappear in the hydrophobic film because the esterification and amidation reactions of polydopamine with propionic anhydride consume the amino and hydroxyl groups in the polydopamine; while the hydrophobic film has an increased characteristic absorption peak at 1713 cm -1 for the stretching vibration of C=O of the polymer, and a stretching vibration peak at 1235 cm -1 for the stretching vibration of the C-O bond, proving the successful preparation of the hydrophobic polymer film.

[0021] When hydrophobic films are prepared using PET substrates and PDMS substrates, the water contact angles are measured respectively: the water contact angle of the PET substrate is 54.7°( Figure 2 a), the water contact angle of the polydopamine film on the PET substrate is 65.1°( Figure 2 b), the water contact angle of the hydrophobic film on the PET substrate is 109.0°( Figure 2 c); the water contact angle of the PDMS substrate is 107.7°( Figure 2 d); the water contact angle of the polydopamine film on the PDMS substrate is 63.8°( Figure 2 e); the water contact angle of the hydrophobic film on the PDMS substrate is 112°( Figure 2 f).

[0022] The method of the present invention grafts acyl groups on the surface of the original polydopamine film to obtain a hydrophobic film. This method is simple, fast, green, and has broad application prospects in various fields such as architectural coatings, biomedicine, purification and environmental protection, and functional textiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Infrared spectrogram of the polydopamine film and the hydrophobic film in Example 1,

[0024] Figure 2 Measurement result diagram of the water contact angle,

[0025] Among them, a is the water contact angle of the PET substrate, which is 54.7°; b is the water contact angle of the polydopamine film on the PET substrate, which is 65.1°; c is the water contact angle of the hydrophobic film on the PET substrate, which is 109.0°; d is the water contact angle of the PDMS substrate, which is 107.7°; e is the water contact angle of the polydopamine film on the PDMS substrate, which is 63.8°; f is the water contact angle of the hydrophobic film on the PDMS substrate, which is 112°. Specific implementation mode

[0026] All the following reagents are commercially available.

[0027] Example 1

[0028] The technical solution for preparing a hydrophobic film by in-situ assembly of dopamine is as follows:

[0029] (1) The first substrate: Pretreatment of the PET substrate

[0030] Cut the PET substrate into several square substrates of 2*2 cm; place the PET substrate in a beaker, and ultrasonically treat it twice with acetone solvent, once with dishwashing liquid, three times with deionized water, and twice with ethanol, each time for 20 minutes. Then use forceps to pick out the PET substrate and dry the surface with a nitrogen gun.

[0031] (2) Preparation of tris(hydroxymethyl)aminomethane hydrochloride buffer solution

[0032] Weigh 0.17 g of tris(hydroxymethyl)aminomethane and 0.09 g of tris(hydroxymethyl)aminomethane hydrochloride into a beaker, add 200 ml of deionized water, and stir at room temperature until completely dissolved. The pH of the solution is 8.0 - 8.5.

[0033] (3) Preparation of the polydopamine film on the substrate surface

[0034] 0.4 g of dopamine hydrochloride was added to the tris(hydroxymethyl)aminomethane hydrochloride buffer solution prepared in the previous step, and stirred to mix well. Then the solution was all poured into a petri dish with the treated PET substrate. After standing at room temperature for 24 h or ultrasonic treatment for 30 min, dopamine undergoes oxidative self-polymerization in a weakly alkaline environment (H Lee, S MDELLATORE, W M MILLER, et al. Mussel-Inspired Surface Chemistry for Multifunctional Coatings [J]. Science, 2007, 318(5849): 426-430.), and finally forms a dense polydopamine film on the substrate surface due to its adhesion. The substrate surface was washed with deionized water and dried with a nitrogen gun to prevent the propionic anhydride in the next secondary reaction from decomposing into propionic acid when encountering water.

[0035] (4) Preparation of a hydrophobic film by secondary in-situ assembly

[0036] The dried substrate at the end of the dopamine self-polymerization reaction was immediately placed in a propionic anhydride solution for 1 h. The polydopamine and propionic anhydride underwent an esterification reaction and an amidation reaction to form a hydrophobic polymer, obtaining a hydrophobic film ( Figure 1 ), and placed in an oven and dried at 60 °C for 12 h.

[0037] Example 2

[0038] The technical solution for preparing a hydrophobic film by in-situ assembly based on dopamine is as follows:

[0039] (1) Preparation of the second substrate: Dow Corning SYLGARD 184 silicone rubber (PDMS) substrate

[0040] The basic component A of PDMS and the curing agent B component were poured into a beaker at a mass ratio of 10:1 (M Ramuz, BC-K.Tee, J B.-H.Tok, et al. Transparent, Optical, Pressure-Sensitive Artificial Skin for Large-Area Stretchable Electronics [J]. Advanced Materials, 2012, 24: 3223–3227.), stirred well with a glass rod, poured into a large petri dish, and left to stand at room temperature for 2 h to remove air bubbles. Then it was placed in an oven and dried at 70 °C for 2-3 h, taken out and cut into a 2*2 cm square substrate.

[0041] Steps (2), (3), and (4) are the same as those in Example 1.

[0042] Performance detection:

[0043] 1) Infrared spectrum test

[0044] The polydopamine thin film and the hydrophobic polymer thin film in Example 1 were subjected to infrared spectrum test, and the test results are as Figure 1 . In the infrared spectrum of the polydopamine thin film, 1510 cm -1 , 1576 cm -1 are the characteristic absorption peaks of N-H shear vibration and bending vibration, and 3435 cm -1 is the stretching vibration peak of N-H; the C=C skeletal characteristic peak in the benzene ring overlaps with the N-H peak at 1576 cm -1 ; 3065 cm -1 is the absorption peak of unsaturated =C-H bond; 3500 cm -1 -3543 cm -1 is the O-H stretching vibration absorption peak; 2903 cm -1 , 2969 cm -1 are the stretching vibration peaks of -CH2-. In the infrared spectrum of the hydrophobic thin film, 1713 cm -1 is the characteristic absorption peak of the C=O stretching vibration of the polymer; 1235 cm -1 is the stretching vibration peak of the C-O bond. By comparing the infrared characteristic peaks of the polydopamine thin film and the hydrophobic thin film, it is found that the characteristic peaks at 1510 cm -1 , 3435 cm -1 , 3500 cm -1 -3543 cm -1 all disappear because the esterification and amidation reactions of polydopamine with propionic anhydride consume the amino and hydroxyl groups in polydopamine, proving the successful preparation of the hydrophobic polymer thin film.

[0045] 2) Measurement of water contact angle

[0046] The water contact angle was measured using the fitting method, and the specific method is as follows:

[0047] ① Place the test sample on the sample stage;

[0048] ② Draw in an appropriate amount of pure water with a microinjector, rotate the liquid inlet knob to form a liquid droplet at the front end of the needle, and rotate the up and down movement knob of the sample stage to make the sample surface contact with the liquid droplet;

[0049] ③ Collect images using the single-shot shooting method;

[0050] ④ Select two points at the left and right ends of the interface between the liquid droplet and the thin film respectively, and automatically draw a reference line;

[0051] ⑤Click on the bottom, middle, and top of one side of the droplet in sequence, and the contact angle value will be automatically fitted and obtained;

[0052] ⑥Mark the corresponding angles and tangents on the picture and save.

[0053] The water contact angle of the prepared PET substrate is 54.7° ( Figure 2 in a)); the water contact angle of the polydopamine film on the prepared PET substrate is 65.1° ( Figure 2 in b)); the water contact angle of the hydrophobic polymer film on the prepared PET substrate is 109.0° ( Figure 2 in c)); the water contact angle of the prepared PDMS substrate is 107.7° ( Figure 2 in d)); the water contact angle of the polydopamine film on the prepared PDMS substrate is 63.8° ( Figure 2 in e)); the water contact angle of the hydrophobic polymer film on the prepared PDMS substrate is 112° ( Figure 2 in f)).

[0054] The technical solution for preparing the hydrophobic film based on in-situ assembly of dopamine described above is only a relatively optimal solution of the present invention, rather than being used to limit the present invention. The polydopamine-modified substrate can also undergo a secondary reaction with alkyl carboxylic acids and alkyl acyl chloride compounds to in-situ assemble into a hydrophobic film. Similarly, the substrate can also be replaced with other materials, such as polypropylene, polyimide, glass, etc. Without departing from the scope of the present invention, the technical solutions obtained by means of equivalent substitution are all within the protection scope of the present invention.

Claims

1. A method for preparing a hydrophobic film based on in-situ assembly of dopamine, comprising the following steps: (1) Providing a substrate; the substrate is a PET substrate or a PDMS substrate; (2) Under weak alkaline conditions, dopamine undergoes an oxidation-crosslinking reaction, self-polymerizes into a polydopamine film that adheres to the surface of the substrate, and the substrate surface is cleaned and dried; the weak alkaline condition is a solution pH of 8.0-8.5; (3) placing the substrate with the polydopamine film in an anhydrous acylating agent solution to undergo esterification and amidation reactions to generate a hydrophobic polymer, thereby obtaining a hydrophobic film on the substrate, wherein the acylating agent is propionic anhydride.

2. The method according to claim 1, wherein the step (2) comprises adding dopamine hydrochloride to tris(hydroxymethyl)aminomethane hydrochloride) buffer solution and stirring to fully mix the solution, then pouring the solution into a surface dish on which a clean and dry substrate has been placed, and allowing the solution to stand and soak for 24 hours at room temperature or ultrasonically treating the solution for 30 minutes. Dopamine undergoes oxidative self-polymerization in a weakly alkaline environment and forms a dense polydopamine film on the surface of the substrate.

3. A hydrophobic film prepared according to any one of claims 1-2.

4. Use of the hydrophobic film according to claim 3 in waterproof materials.

5. The use according to claim 4, wherein the waterproof material is architectural coating, biomedicine, purification and environmental protection, or functional textiles.

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