Transparent fluorine-free liquid-repellent and stain-resistant coating and preparation method thereof

Abstract

This invention relates to a transparent, fluorine-free, hydrophobic, and antifouling coating. The antifouling coating comprises a transition layer, a SiO2-like structure, and a PDMS-like structure, forming a gradient structure. The SiO2-like structure is the main body of the coating, with an organic / inorganic structure ratio between 0.05 and 0.3 and a silicon / oxygen ratio between 0.28 and 0.38. The PDMS-like structure includes periodic Si(CH3)2 repeating units, with an organic / inorganic structure ratio between 0.4 and 3.0 and a silicon / oxygen ratio between 0.4 and 0.7. The coating of this invention has a gradient structure, meaning that at the top of the coating, there is a gradual transition from a highly cross-linked structure to a less cross-linked structure. The highly cross-linked region has high hardness and rigidity, resisting external forces, while the less cross-linked region provides the coating with excellent hydrophobic properties.

Description

Technical Field

[0001] This invention relates to the field of polymer coatings, and more particularly to a transparent, fluorine-free, hydrophobic, and antifouling coating and its preparation method. Background Technology

[0002] Hydrophobic and oleophobic coatings play a vital role in daily life and industry, with potential applications in antifouling, corrosion resistance, anti-icing, and separation. They achieve their hydrophobic and oleophobic effects primarily by reducing the surface energy of the material. Oils have even lower surface tension, typically between 20 and 30 mN / m, making the preparation of oleophobic coatings more challenging than that of hydrophobic coatings. Currently, oleophobic coatings are often prepared using fluoropolymers; however, fluoropolymers tend to be bioaccumulative, posing significant risks to human health and the environment, thus their use is increasingly being restricted by regulations.

[0003] There are three main methods for preparing oleophobic surfaces: dual superhydrophobic coatings, liquid surfaces, and liquid-like surfaces. 1) Superhydrophobic / single-hydrophobic coatings (SHPS / SOPS) are mainly prepared by combining low surface energy coatings with micro / nano structures, utilizing an air layer to achieve a hydrophobic effect. However, the air layer is unstable and loses its original function under high pressure; furthermore, the micro / nano structures are easily damaged and difficult to repair, resulting in poor durability of this type of coating. 2) Liquid surfaces, represented by liquid-injected surfaces (SLIPS), involve injecting low surface energy lubricants into porous surfaces to form a smooth liquid layer. This allows the coating to resist any liquid incompatible with the lubricant. However, problems such as lubricant evaporation and contamination can lead to performance failure, limiting long-term use. 3) In addition to the two coatings mentioned above, there is also a liquid-like surface (LLS) with surface-tethered flexible polymer chains. When the flexible polymer chains on the surface come into contact with liquids with low surface tension, they undergo conformational rearrangement, thereby generating dynamic oleophobic properties. Furthermore, the liquid-like surface does not need to consider the loss of surface micro-nano structures and surface lubricants. Therefore, it has significant advantages over the former two in practical applications.

[0004] However, liquid-like surfaces are often prepared by grafting, resulting in thin coatings with dimensions of only a few to tens of nanometers, which limits their mechanical durability. In addition, due to steric hindrance during grafting, the flexible polymer segments on the surface may not be evenly covered, resulting in surface chemical heterogeneity. Furthermore, the surface roughness of the substrate can also cause structural heterogeneity, making it easy for pinning and other obstacles to droplet sliding to occur during the liquid-repellent process.

[0005] Therefore, developing a durable, fluorine-free liquid surface with good liquid-repellent (hydrophobic and oleophobic) properties, as well as self-smoothing and chemical homogeneity, is of great significance. Summary of the Invention

[0006] The present invention aims to provide a transparent, fluorine-free, hydrophobic, and antifouling coating and its preparation method, so as to overcome the shortcomings of the prior art. The technical problem to be solved by the present invention is achieved through the following technical solution.

[0007] This invention proposes a transparent, fluorine-free, hydrophobic, and antifouling coating. The transition layer employs an organic coating with different main chains depending on the substrate being coated. The antifouling coating comprises a transition layer, a gradient structure of a SiO2-like structure, and a PDMS-like structure. The SiO2-like structure forms the main body of the coating, with an organic / inorganic structure ratio between 0.05 and 0.3 and a silicon / oxygen ratio between 0.28 and 0.38. The PDMS-like structure includes periodic Si(CH3)2 repeating units, with an organic / inorganic structure ratio between 0.4 and 3.0 and a silicon / oxygen ratio between 0.4 and 0.7.

[0008] Furthermore, the coating substrate is an inorganic material or an organic material. The inorganic material is selected from glass, ceramics, stainless steel, copper, aluminum, and iron, and the organic material is selected from polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), polystyrene (PS), polycarbonate (PC), polyurethane (PU), rubber, natural polymers, or PMMA.

[0009] When the coating substrate is an inorganic material, the transition layer is an organosilicon coating with Si and O as the main chains; when the coating substrate is an organic material, the transition layer is an organic coating with CC chains as the main chains.

[0010] Furthermore, the internal structure of the antifouling coating gradually transforms from a PDMS-like structure in the transition layer to a SiO2-like structure and then back to a PDMS-like structure.

[0011] Furthermore, the proportions of Si-(O)3 and Si-(O)4 in the SiO2-like structure are in the range of 70% to 95%.

[0012] Furthermore, the organic / inorganic structure ratio in the characterization test Silicon bonding.

[0013] Furthermore, the transition layer, the SiO2-like structure, and the PDMS-like structure are all prepared continuously using a vapor-phase method.

[0014] Another aspect of the present invention provides a method for preparing a transparent, fluorine-free, hydrophobic, and antifouling coating, comprising the following steps:

[0015] S1: After cleaning and drying the substrate, place it in the plasma chamber, then close the chamber and evacuate it.

[0016] S2: Introduce activation gas and plasma to clean and activate the substrate surface again, increase the substrate surface temperature, then turn off the plasma and remove additional gas.

[0017] S3: Introduce precursor A and auxiliary reactive gas D, input plasma, and complete the deposition of plasma polymer transition layer;

[0018] S4: Adjust the plasma power and deposition pressure, and simultaneously input precursor B and auxiliary reactive gas E for deposition. Then turn off auxiliary reactive gas D and precursor A in sequence to complete the deposition of the SiO2-like layer with cross-linked structure.

[0019] S5: Adjust the deposition pressure, introduce precursor C, deposit for several minutes, turn off precursor B, adjust the plasma power, deposit for several more minutes, turn off the plasma input and all monomer inputs, exhaust the waste gas, break the vacuum, and then complete the preparation of a linear PDMS-like layer with structural gradient.

[0020] The deposition process from step S3 to step S5 is continuous and uninterrupted.

[0021] The precursor A is a mixture of one or more systems, such as linear hydrocarbons and linear organosilanes, with a saturated vapor pressure of not less than 2.5 kPa at 20°C, including but not limited to the following monomers: tetraethyl orthosilicate, pentamethyldisiloxane, hexamethyldisiloxane, hexamethyldisilazane, bis(trimethylsiloxymethylsilane), octamethyltrisiloxane, 1,1,3,3-tetramethyldisiloxane, tetramethyldivinyldisiloxane, vinylpentamethyldisiloxane, 1,3-diethyl-1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,5-divinyl-hexamethyltrisiloxane, 1-vinyl-1,1,3,3-tetramethyldisiloxane, silane, methane, ethane, hexafluoropropylene, hexafluorobutyl acrylate, acrylic acid, and butyl methacrylate.

[0022] The precursor B is one or a mixture of two or more organosilane monomers having one or more rings. The relative silicon content in precursor B is greater than 40%, and its saturated vapor pressure at 20°C is not less than 0.1 kPa, including but not limited to the following monomers: 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, octamethylcyclotetrasiloxane, 2,4,6,8-tetramethyltetravinylcyclotetrasiloxane, heptamethylcyclotetrasiloxane, 2,4,6,8,10-cyclopentasiloxane, and acetoxyheptamethylcyclotetrasiloxane;

[0023] The precursor C is a linear organosilicon monomer with a main chain of -Si-O-, including but not limited to the following monomers: pentamethyldisiloxane, hexamethyldisiloxane, bis(trimethylsiloxymethylsilane), octamethyltrisiloxane, 1,1,3,3-tetramethyldisiloxane, tetramethyldivinyldisiloxane, vinylpentamethyldisiloxane, 1,3-diethyl-1,1,3,3-tetramethyldisiloxane, 1-allyl-1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,5-divinyl-hexamethyltrisiloxane, 1-vinyl-1,1,3,3-tetramethyldisiloxane, and 1,3-di(chloromethyl)-1,1,3,3-tetramethyldisiloxane.

[0024] The auxiliary reaction gases D and E are one or a mixture of two or more of Ar, O2, N2, H2O, H2O2, and H2.

[0025] Furthermore, the time interval between shutting off the auxiliary reaction gas D, opening the precursor C, and shutting off the precursor B is 10–300 s, and the deposition time from shutting off the precursor B to the end of deposition is 60–900 s.

[0026] The "liquid-like" coating of this invention exhibits high transparency, excellent dynamic hydrophobic properties, and mechanical durability. The dynamic hydrophobicity ("liquid-like") is primarily attributed to: 1) the PDMS-like structure (i.e., Si(O)₂ structure) on its surface, which possesses good fluidity at room temperature. Upon contact with a droplet, the polymer chains on the surface undergo conformational rearrangement, creating regional surface energy inhomogeneity at the triple line, facilitating rapid droplet sliding at extremely low tilt angles; 2) the extremely low surface roughness (sub-nanometer level) significantly reduces the resistance during droplet sliding. The low surface roughness also ensures extremely low light scattering and high light transmittance. Furthermore, the SiO₂-like structure in the coating's gradient structure endows the coating with excellent mechanical properties, giving it significantly higher hardness and wear resistance compared to ordinary polymer coatings.

[0027] This invention features a gradient structure, where the coating top layer gradually transitions from a highly cross-linked structure to a less cross-linked structure. The highly cross-linked region (a SiO2-like structural layer) exhibits high hardness and rigidity, resisting external forces, while the less cross-linked region (a PDMS-like structural layer) provides excellent hydrophobic properties. This gradient structure effectively mitigates problems such as modulus mismatch between coatings with different structures. Furthermore, it reduces internal stress mismatch when resisting external forces, effectively improving issues like internal delamination and cracking within the coating. Attached Figure Description

[0028] Figure 1 SEM images of (a) Example 1, (b) Example 2 and (c) Comparative Example 1;

[0029] Figure 2 AFM plots for (a) Example 1 and (b) Comparative Example 1;

[0030] Figure 3 UV-Vis graphs for Example 1 and Comparative Example 1;

[0031] Figure 4 Cross-sectional views of (a) Example 1 and (b) Comparative Example 1;

[0032] Figure 5 The diagrams show the Si 2p structures of (a) SiO2-like structures and (b) PDMS-like structures in Example 1.

[0033] Figure 6 The sliding angles after friction tests for Example 1, Comparative Example 5, Comparative Example 7, and Comparative Example 8;

[0034] Figure 7 XPS depth element analysis for Example 1;

[0035] Figure 8 For the anti-fouling test of Example 2;

[0036] Figure 9 The effect of coating the inside of the glass with the coating of Example 2 on the repulsion of chili oil;

[0037] Figure 10 Example 2 shows the rejection effect of quick-drying printing ink. Detailed Implementation

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] One specific embodiment of the present invention proposes a transparent, fluorine-free, hydrophobic, and antifouling coating, comprising a transition layer, a SiO2-like structure, and a PDMS-like structure in a gradient transition structure. The internal structure of the coating gradually transitions from the transition layer to the SiO2-like structure and then to the PDMS-like structure. The SiO2-like structure constitutes the main body of the coating, wherein the organic / inorganic structure ratio is determined by the silicon bonding characteristics measured in the characterization test. With a silicon / oxygen ratio between 0.05 and 0.3, and a silicon / oxygen ratio between 0.28 and 0.38, this part of the structure has a high number of SiO bonds and cross-linking units, thus exhibiting greater rigidity and better mechanical properties; the PDMS-like structure includes periodic Si(CH3)2 repeating units, in which the organic / inorganic structure accounts for a certain percentage. Between 0.4 and 3.0, and between 0.4 and 0.7, the structure contains a large number of repeating Si(CH3)2 units. The coating composed of this part of the structure has a low glass transition temperature. The polymer chains have high fluidity at room temperature and undergo conformational rearrangement when in contact with droplets, resulting in uneven surface energy at the solid-liquid-gas triple phase line. This reduces the resistance when the droplets slide, allowing the droplets to slide off the surface quickly at extremely low tilt angles.

[0040] The three-layer structure required by this invention includes a transition layer, a SiO2-like structural layer, and a PDMS-like structural layer. The three layers are prepared continuously using a vapor-phase method. After the transition layer is prepared, its surface must have a large number of residual active sites. These residual active sites are used to regulate the surface structure of the SiO2-like structural layer. Without this transition layer, the SiO2-like structural layer will produce a large number of disordered structures, affecting the final coating performance. The transition layer should be an organic coating with a different main chain structure for the substrate. For example, when coating on glass or other surfaces, the transition layer should be an organosilicon coating with Si and O as the main chains; when coating on PMMA (plexiglass) or other substrates, the transition layer should be an organic coating with CC chains as the main chains. The similar structure and composition of the transition layer and the substrate ensure good matching between the prepared coating and the substrate, avoiding cracking and blistering of the coating under harsh operating conditions.

[0041] The coating in this embodiment has good liquid-repellent properties, with a sliding angle of <10° for water (20μL) and <6° for other liquids (10μL), and a light transmittance of >90%, and a light transmittance of >99.5% after subtracting the substrate.

[0042] The specific preparation method of the above coating is described below, including the following steps:

[0043] S1: Different substrates are cleaned and dried according to their respective properties using different methods, and then placed in the plasma chamber. The chamber is then closed, and the mechanical pump is turned on to evacuate the vacuum.

[0044] The substrate materials include, but are not limited to, polymeric materials such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), polystyrene (PS), polycarbonate (PC), polyurethane (PU), rubber, and natural polymers; inorganic non-metallic materials such as glass and ceramics; metallic materials such as stainless steel, copper, aluminum, and iron; and devices such as circuit boards and micro / miniature sensors. Their shapes include, but are not limited to, spherical, regular, and irregular shapes.

[0045] S2: Introduce activation gas and plasma to clean and activate the substrate surface again, and appropriately increase the substrate surface temperature. Then turn off the plasma and remove the additional gas.

[0046] The activating gas is one or a mixture of two or more of O2, N2, He, Ar, and Ne. In this embodiment, the activating gas is O2 and Ar.

[0047] S3: Introduce precursor A and auxiliary reactive gas D, input plasma, and deposit for several minutes to complete the deposition of the plasma polymer transition layer.

[0048] Precursor A is a mixture of one or more systems, such as hydrocarbons with linear structures and organosilanes with linear structures, with a saturated vapor pressure of not less than 2.5 kPa at 20°C. Precursor A includes, but is not limited to, the following monomers: tetraethyl orthosilicate, pentamethyldisiloxane, hexamethyldisiloxane, hexamethyldisilazane, bis(trimethylsiloxymethylsilane), octamethyltrisiloxane, 1,1,3,3-tetramethyldisiloxane, tetramethyldivinyldisiloxane, vinylpentamethyldisiloxane, dimethoxymethylvinylsilane, 1,3-diethyl-1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,5-divinyl-hexamethyltrisiloxane, 1-vinyl-1,1,3,3-tetramethyldisiloxane, silane, methane, ethane, hexafluoropropylene, hexafluorobutyl acrylate, acrylic acid, and butyl methacrylate. Precursor A is preferably a silicon / carbon monomer with a linear structure and a low silicon content, which is beneficial to improving the surface uniformity of the prepared coating and reducing roughness.

[0049] The auxiliary reactant gas D is one or a mixture of two or more of Ar, O2, N2, H2O, H2O2, and H2. In this embodiment, the auxiliary reactant gas D is Ar, O2, and N2.

[0050] S4: Adjust the plasma power and deposition pressure, and simultaneously input precursor B and auxiliary reaction gas E. Then turn off auxiliary reaction gas D and precursor A in sequence. Deposit for several minutes to complete the deposition of the SiO2-like layer with cross-linked structure.

[0051] The auxiliary reactant gas E is one or a mixture of two or more of Ar, O2, N2, H2O, H2O2, and H2. In this embodiment, the auxiliary reactant gas E is Ar and O2.

[0052] Precursor B is one or a mixture of two or more organosilane monomers having one or more rings. The relative silicon content in precursor B is greater than 40%, and its saturated vapor pressure at 20°C is not less than 0.1 kPa. Precursor B includes, but is not limited to, the following monomers: 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, octamethylcyclotetrasiloxane, 2,4,6,8-tetramethyltetravinylcyclotetrasiloxane, heptamethylcyclotetrasiloxane, 2,4,6,8,10-cyclopentasiloxane, and acetoxyheptamethylcyclotetrasiloxane.

[0053] In this embodiment, auxiliary reaction gases D and E are O2. In other embodiments, auxiliary reaction gases D and E are one or more mixtures selected from Ar, O2, N2, H2O, H2O2, CH4, and C2H2. Preferably, auxiliary reaction gas D is Ar, O2, H2O, or H2O2, and auxiliary reaction gas E is Ar and O2.

[0054] The coating deposited in step S4 is a cross-linked hard SiO2 coating, which improves the overall hardness of the coating. Appropriately increasing the pressure and power and reducing the flow rate can prolong the residence time of the fractured particles on the substrate surface, making the formed -SiO- network more biased towards Si(O)4, increasing the density of the coating, and resulting in a coating with higher hardness.

[0055] In step S4, the silicon molar mass ratio of precursor B is greater than 40%, and Si cannot be discharged from the cavity in the form of SiH4 gas. This makes the deposition rate of precursor B greater than that of precursor A. Furthermore, precursor B contains a -SiO- polycyclic structure. When depositing the coating at low plasma power density, the high bond energy of the -SiO- bonds makes it difficult for the -SiO- ring structure to open, easily forming highly adhesive and active polycyclic structures that are prone to aggregation. Coatings grown on the substrate surface using the Volmer-Weber or Stranski-Krastanov method result in a large surface roughness.

[0056] However, because a smooth coating of linear precursor A from step S3 is deposited first as a transition layer, the density of free radicals on the substrate surface is increased. Furthermore, during the deposition of precursor A, precursor A decomposes to produce free hydrogen, which reacts with the deposited coating, increasing surface active sites and raising the substrate surface temperature. Therefore, during the continuous deposition of the high-silicon-content precursor B, the surface free radical sites inhibit the diffusion and aggregation of active polycyclic structures on the substrate surface, allowing precursor B to grow in a Frank van der Merwe manner, thus reducing the generation of surface rough structures.

[0057] S5: Adjust the deposition pressure, introduce precursor C, deposit for several minutes, turn off precursor B, adjust the plasma power, deposit for several more minutes, turn off the plasma input and all monomer inputs, exhaust the waste gas, break the vacuum, and then complete the preparation of a linear PDMS-like layer with structural gradient.

[0058] In step S5 above, the precursor C is a linear organosilicon monomer with a main chain of -SiO-, including but not limited to the following monomers: pentamethyldisiloxane, hexamethyldisiloxane, bistrimethylsiloxymethylsilane, octamethyltrisiloxane, 1,1,3,3-tetramethyldisiloxane, tetramethyldivinyldisiloxane, vinylpentamethyldisiloxane, 1,3-diethyl-1,1,3,3-tetramethyldisiloxane, 1-allyl-1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,5-divinyl-hexamethyltrisiloxane, 1-vinyl-1,1,3,3-tetramethyldisiloxane, and 1,3-di(chloromethyl)-1,1,3,3-tetramethyldisiloxane.

[0059] In a preferred embodiment, the precursor C contains one or more weak bonds, including but not limited to silicon-hydrogen bonds, carbon-carbon double bonds, hydroxyl groups, amino groups, carboxyl groups, and halogen bonds.

[0060] In step S5 above, the time interval between shutting off the auxiliary reactive gas D, turning on the precursor C, and shutting off the precursor B is 10–300 s; in this embodiment, the time interval is 60–180 s, and the flow rate of the precursor C is 10–20 sccm. The pressure adjusted after shutting off the auxiliary reactive gas D is 30–200 Pa; in this embodiment, the pressure is adjusted to 50–100 Pa. The deposition time from shutting off the precursor B to the end of deposition is 60–900 s; in this embodiment, the deposition time is 300–600 s. After shutting off the precursor B, the plasma power density is adjusted to 1.0–5.0 kW / m³. 2 In this embodiment, the plasma power density is 1.0–2.0 kW / m³. 2 The pressure remains at 50–100 Pa.

[0061] In step S5 above, when depositing the linear PDMS-like layer, the input plasma power and deposition pressure should not be too high, so that the prepared PDMS-like layer can have as many -O-Si-O- chains as possible, and the surface layer forms a certain high proportion of high-flowability PDMS polymer chains (repeating units ≥15).

[0062] The deposition process from steps S3 to S5 described above is continuous and uninterrupted.

[0063] The present invention will now be described in further detail with reference to Examples 1-5 and Comparative Examples 1-8.

[0064] Example 1: Cleaned and dried glass slides, silicon wafers, dimethyl polycarbonate, and polished stainless steel plates (2.5×2.5cm) were hung on the sample holder as required. The cavity was closed, and the mechanical pump was turned on to evacuate the sample to a pressure of 1 Pa. The cavity was then opened and rotated, and O2:Ar was introduced into the cavity at a flow ratio of 1:4, with an input of 3.0 kW / m³. 2 The plasma was used to clean and activate the substrate for 300 seconds, with the temperature raised to 50°C. The chamber pressure was then evacuated back to 1 Pa. Precursor A and auxiliary gas D were then turned on. In this embodiment, precursor A is dimethoxymethylvinylsilane, with a flow ratio of 2:1 and a total flow rate of 15 sccm. The pressure was maintained at 50 Pa. Plasma was then input, and the plasma power was adjusted to 4.0 kW / m³. 2 A transition layer was deposited for 600 seconds. Then, precursor A and auxiliary gas D were shut off, while precursor B and auxiliary gas E were turned on. In this embodiment, precursor B was octamethylcyclotetrasiloxane, with a flow ratio of 1:1, a total flow rate of 10 sccm, a reaction pressure of 70 Pa, and a plasma power density adjusted to 3.0 kW / m³. 2 The deposition time was 600 s. Then, the auxiliary gas E was turned off, and the precursor C was turned on. In this embodiment, the precursor C was 1,3-di(chloromethyl)-1,1,3,3-tetramethyldisiloxane, with a flow rate of 10 sccm, a reaction pressure of 50 Pa, and a plasma power adjustment of 2.0 kW / m³. 2 The deposition time was 60 seconds. Precursor B was turned off, and the plasma power was adjusted to 1.5 kW / m³. 2 Maintain a pressure of 50 Pa and deposit for 300 s. Then, complete the coating preparation. Turn off the air inlet and plasma input, remove the waste gas from the chamber to below 10 Pa, turn off the vacuum pump, break the vacuum, open the chamber, turn off the rotation, and take out the sample.

[0065] Example 2: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. The ratio of precursor B to auxiliary gas E in step S4 was adjusted to 1:2, the total flow rate was 10 sccm, the reaction pressure was adjusted to 100 Pa, and the plasma power density was adjusted to 6.5 kW / m³. 2 The remaining process is the same as in Example 1.

[0066] Example 3: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. The ratio of precursor B to auxiliary gas E in step S4 was adjusted to 3:1, the total flow rate was 10 sccm, the reaction pressure was 50 Pa, and the plasma power density was adjusted to 2.0 kW / m³. 2 The remaining process is the same as in Example 1.

[0067] Example 4: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. The reaction pressure in step S5 was adjusted to 150 Pa, and the plasma power density after shutting down precursor B was adjusted to 4.0 kW / m³. 2 The deposition time was adjusted to 600s, and the rest of the process was the same as in Example 1.

[0068] Example 5: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. After shutting off precursor B in step S5, the flow rate of precursor C was increased to 20 sccm, and the plasma power density after shutting off precursor B was adjusted to 1.0 kW / m³. 2 The deposition time was adjusted to 600s, and the rest of the process was the same as in Example 1.

[0069] Table 1 shows the organic / inorganic structure ratio and silicon / oxygen ratio of each sample from Examples 1-5. The coating structure obtained in Example 1 gradually transitions from a PDMS-like structure in the transition layer to a SiO2-like structure and then back to a PDMS-like structure. The SiO2-like structure, and the organic / inorganic structure ratio (indicated by silicon bonding in characterization tests), are also shown. The ratio of silicon to oxygen is 0.12, and the silicon / oxygen ratio is 0.286. The PDMS-like structure includes periodic Si(CH3)2 repeating units, with the organic / inorganic structure accounting for a certain percentage. The ratio of silicon to oxygen is 0.74, and the ratio of organic to inorganic structures is 0.42. In Example 2, the proportion of organic / inorganic structures resembling SiO2 is 0.05, and the proportion of organic / inorganic structures resembling PDMS is 0.75; in Example 3, the proportion of organic / inorganic structures resembling SiO2 is 0.3, and the proportion of organic / inorganic structures resembling PDMS is 0.73; in Example 4, the proportion of organic / inorganic structures resembling SiO2 is 0.124, and the proportion of organic / inorganic structures is 0.4; in Example 5, the proportion of organic / inorganic structures resembling SiO2 is 0.131, and the proportion of organic / inorganic structures resembling PDMS is 3.

[0070] Table 1. Organic / inorganic structure ratio and silicon / oxygen ratio in Examples 1-5

[0071]

[0072]

[0073] Comparative Example 1: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. Step S3 was omitted, and the remaining procedures were the same as in Example 1. The obtained coating internal structure included a SiO2-like structure and a PDMS-like structure, but without a transition layer. The organic / inorganic structure ratio in the SiO2-like structure (characterized by silicon bonding in characterization tests) is shown in the figure. The ratio is 0.128, and the silicon / oxygen ratio is in the range of 0.284.

[0074] Comparative Example 2: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. Step S4 was omitted, and the remaining processes were the same as in Example 1. The resulting coating internal structure included a transition layer and a PDMS-like structure, but did not contain a SiO2-like structure. The PDMS-like structure included periodic Si(CH3)2 repeating units, with an organic / inorganic structure ratio of The value is 0.72, and the silicon / oxygen ratio is 0.45.

[0075] Comparative Example 3: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. Step S5 was omitted, and the remaining processes were the same as in Example 1. The resulting coating internal structure included a SiO2-like structure and a transition layer, but did not contain a PDMS-like structure. The PDMS-like structure included periodic Si(CH3)2 repeating units, with an organic / inorganic structure ratio of The value is 0.131, and the silicon / oxygen ratio is 0.287.

[0076] Comparative Example 4: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. The ratio of precursor B to auxiliary gas E in step S4 was adjusted to 3:7, the total flow rate was 10 sccm, the reaction pressure was adjusted to 100 Pa, and the plasma power density was adjusted to 6.0 kW / m³. 2 The remaining processes are the same as in Example 1. The proportion of organic / inorganic structures with SiO2-like structures. The ratio of organic to inorganic structures in the PDMS-like structure is 0.04. It is 0.73.

[0077] Comparative Example 5: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. The ratio of precursor B to auxiliary gas E in step S4 was adjusted to 5:1, the total flow rate was 10 sccm, the reaction pressure was adjusted to 50 Pa, and the plasma power density was adjusted to 1.0 kW / m³. 2 The remaining processes are the same as in Example 1. The proportion of organic / inorganic structures with SiO2-like structures. The ratio is 0.6, representing the proportion of organic / inorganic structures in the PDMS-like structure. It is 0.72.

[0078] Comparative Example 6: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. The flow rate of precursor C in step S5 was adjusted to 5 sccm, the reaction pressure was adjusted to 100 Pa, and the plasma power density after precursor B was turned off was adjusted to 3.0 kW / m³. 2The deposition time was adjusted to 600 s, and the rest of the process was the same as in Example 1. The proportion of organic / inorganic structures with SiO2-like structures was also discussed. The ratio of organic to inorganic structures in the PDMS-like structure is 0.15. It is 0.35.

[0079] Comparative Example 7: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. After shutting off precursor B in step S5, the flow rate of precursor C was increased to 20 sccm, the reaction pressure was adjusted to 30 Pa, and the plasma power density after shutting off precursor B was adjusted to 0.5 kW / m³. 2 The deposition time was adjusted to 600 s, and the rest of the process was the same as in Example 1. The proportion of SiO2-like organic / inorganic structures... The ratio of organic to inorganic structures in the PDMS-like structure is 0.14. It is 3.3.

[0080] Comparative Example 8: The same substrate as in Example 1 was hung in the cavity and evacuated to the same vacuum level. Step S5 was modified as follows: the plasma input was turned off, the precursor B and auxiliary reaction gas D were turned off, the cavity pressure was evacuated to 1 Pa and maintained for 600 s, and then the precursor C was introduced at a flow rate of 10 sccm, the reaction pressure was 50 Pa, and the plasma power was 1.5 kW / m². 2 The pressure was maintained at 50 Pa, and deposition was carried out for 300 s. The remaining process was the same as in Example 1. The percentage of organic / inorganic structures with SiO2-like structures was also discussed. The ratio of organic to inorganic structures in the PDMS-like structure is 0.14. It is 0.71.

[0081] The UV-Vis transmittance of the coatings deposited on glass in Example 1 and Comparative Example 1 was tested. When precursor B was deposited directly without a transition layer, a large number of rough microstructures were generated on the surface, such as... Figure 1 and Figure 2 As shown, this will severely affect the light transmittance of the coating, which also demonstrates the significance of the transition layer, such as... Figure 3 As shown, after removing the substrate, Example 1 has a transmittance of more than 99.5% in the visible light range (390-780nm); while Comparative Example 1, due to the absence of a transition layer, has a SiO2-like structure layer with micro-nano structure, which increases light reflection on its surface and reduces the overall transmittance.

[0082] like Figure 5 As shown in Table 2, the Si 2p spectra of the SiO2-like structure and the PDMS-like structure in Example 1 were obtained after XPS analysis. The proportion of different silicon bonds was calculated, and the proportion of organic / inorganic structures in the coating structure was calculated accordingly. The proportions (where the SiO bond energy is 101.1 eV, the Si-(O)2 bond energy is 102.1 eV, the Si-(O)3 bond energy is 102.8 eV, and the Si-(O)4 bond energy is 103.4 eV). (The XPS test sample with the SiO2-like structure is the Example 1 sample without step S5 deposition). Table 2 shows the area of ​​different bonding states after peak separation of the Si 2p spectra of the SiO2-like structure and the PDMS-like structure in Example 1, and the proportion of their respective organic / inorganic structures.

[0083]

[0084] Referring to the national standard GB / T 24368-2229, the samples were tested for contact angle (5 μL) with water and hexadecane, and for roll-off angle (20 μL water, 10 μL hexadecane). The liquid repellency data are shown in Table 3. All examples and Comparative Example 2 showed good liquid repellency. Comparative Example 3 had a certain contact angle with hexadecane, but when the substrate was tilted, the droplet could not slide off without leaving a trace, and there was a serious droplet tailing phenomenon. The reason for this phenomenon is mainly that the former has abundant flexible -OS iO- PDMS segments on its surface, which is a typical liquid-like surface structure. Although the surface of Comparative Example 1 also contains abundant flexible -OS iO- PDMS segments, its rough surface structure increases the static oleophilicity, and the rough structure increases the steric hindrance of droplet sliding, thus making it unable to remove hexadecane. The latter does not have abundant PDMS segments on its surface and contains more -CH3, exhibiting extremely high oleophilicity.

[0085] To achieve an organic / inorganic ratio of less than 0.05 for the SiO2-like structure, a large proportion of oxygen and high plasma power were introduced during the SiO2-like structure deposition process in Comparative Example 4. This intensified particle oxidation during deposition, generating particles with high affinity. These particles attracted each other to form dust, which then easily adsorbed onto the substrate, resulting in a coating containing a large number of adsorbed particles and forming a superhydrophobic coating. Since the particles are not chemically bonded to the surface, they are easily broken, and water droplets exhibit a pinning effect. Furthermore, the lipophilic group of -CH3 provided in step S5 also resulted in complete wetting of hexadecane on its surface, making it impossible to remove.

[0086] Table 3. Hydrophobic properties of all samples

[0087]

[0088]

[0089] As shown in Table 4, the pencil hardness of Examples 1-3 all reached 4H, which is a significant improvement compared to Comparative Example 2. This is because the addition of a cross-linked SiO2-like layer in the middle of the examples greatly enhances the coating hardness. Compared to Comparative Example 5, the organic / inorganic component of the SiO2-like structure in Comparative Example 5 is greater than 0.3, resulting in a lower degree of cross-linking and consequently a decrease in coating hardness.

[0090] Table 4. Pencil hardness of Examples 1-3, Comparative Examples 2 and 5

[0091] Example 1 Example 2 Example 3 Comparative Example 2 Comparative Example 5 Pencil hardness 4H 4H 4H 3B 1B

[0092] like Figure 6 As shown, after the cotton abrasion test of Example 1 and Comparative Examples 5, 7 and 8, the overall mechanical strength and mechanical durability of the coating were reduced because the organic / inorganic component of the SiO2-like structure in Comparative Example 5 was greater than 0.3; the organic / inorganic component of the PDMS-like structure in Comparative Example 7 was greater than 3, and the excessively long PDMS chain segments made it very easy to break during the friction test, resulting in surface chemical heterogeneity, which would affect the dynamic hydrophobic properties of the coating. Figure 7 XPS depth elemental analysis of the sample of Example 1 showed that Example 1 has a good gradient structure. Since there is no gradient structure between the SiO2-like structure and the PDMS-like structure in Comparative Example 8, PDMS bonds in Comparative Example 8 are very easy to break during the friction process.

[0093] Figures 8-10 The self-cleaning properties and the ability to repel oils from daily life were demonstrated in Example 2 on different substrates, exhibiting good hydrophobic and antifouling properties.

[0094] In summary, this application utilizes PECVD to prepare a single-step, durable, nano-gradient liquid-like coating with controllable thickness and cross-linked SiO2-like and linear PDMS-like structures. This coating exhibits excellent hydrophobic and antifouling properties, with a water contact angle of approximately 108° and an oil roll-off angle of less than 10°. The coating achieves a film-substrate adhesion rating of 5B, a pencil hardness of 4H, and a hardness of 1 GPa. The transition layer effectively improves the high roughness of coatings prepared from cyclic siloxane monomers during plasma polymerization, resulting in a surface roughness of less than 1 nm and high light transmittance. Furthermore, the use of a continuous gradient method to prepare the nano-gradient structure effectively enhances the durability of the prepared liquid-like coating.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., 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 transparent, fluorine-free, hydrophobic, and antifouling coating, characterized in that, The antifouling coating includes a transition layer, a SiO2-like structure, and a PDMS-like structure with a gradient structure. The gradient structure is characterized by components that gradually transition from a highly cross-linked structure to a low cross-linked structure at the top of the coating. The intralayer structure of the antifouling coating gradually changes from the smooth plasma polymer coating of the transition layer to a SiO2-like structure and then to a PDMS-like structure. When the substrate is an inorganic material, the transition layer is an organosilicon coating with Si and O as the main chains; when the substrate is an organic material, the transition layer is an organic coating with CC chains as the main chains. The SiO2-like structure forms the main body of the antifouling coating, wherein the organic / inorganic structure ratio is between 0.05 and 0.3, and the silicon / oxygen ratio is between 0.28 and 0.

38. The PDMS-like structure includes periodic Si(CH3)2 repeating units, wherein the organic / inorganic structure ratio is between 0.4 and 3.0, and the silicon / oxygen ratio is between 0.4 and 0.

7. The organic / inorganic structure ratio is used in characterization tests to determine silicon bonding. Compare.

2. The transparent, fluorine-free, hydrophobic, and antifouling coating as described in claim 1, characterized in that, The coating substrate is an inorganic or organic material. The inorganic material is selected from glass, ceramics, stainless steel, copper, aluminum, and iron. The organic material is selected from polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), polystyrene (PS), polycarbonate (PC), polyurethane (PU), natural polymers, or PMMA.

3. The transparent, fluorine-free, hydrophobic, and antifouling coating as described in claim 1, characterized in that, The SiO2-like structure contains Si-(O)3 and Si-(O)4 in a proportion of 70% to 95%.

4. The transparent, fluorine-free, hydrophobic, and antifouling coating as described in claim 1, characterized in that, The transition layer, the SiO2-like structure, and the PDMS-like structure were all prepared continuously using a vapor-phase method.

5. A method for preparing a transparent, fluorine-free, hydrophobic, and antifouling coating as described in any one of claims 1-4, characterized in that, Includes the following steps: S1: After cleaning and drying the substrate, place it in the plasma chamber, then close the chamber and evacuate it. S2: Introduce activation gas and plasma to clean and activate the substrate surface again, increase the substrate surface temperature, then turn off the plasma and remove additional gas. S3: Introduce precursor A and auxiliary reactive gas D, input plasma, and complete the deposition of plasma polymer transition layer; S4: Adjust the plasma power and deposition pressure, and simultaneously input precursor B and auxiliary reactive gas E for deposition. Then turn off auxiliary reactive gas D and precursor A in sequence to complete the deposition of the SiO2-like layer with cross-linked structure. S5: Adjust the deposition pressure, introduce precursor C, deposit for several minutes, turn off precursor B, adjust the plasma power, deposit for several more minutes, turn off the plasma input and all monomer inputs, exhaust the waste gas, break the vacuum, and then complete the preparation of a linear PDMS-like layer with structural gradient. The deposition process from step S3 to step S5 is continuous and uninterrupted.

6. The method for preparing the transparent, fluorine-free, hydrophobic, and antifouling coating as described in claim 5, characterized in that: The precursor A is a mixture of one or more of a linear hydrocarbon system and a linear organosilane system, with a saturated vapor pressure of not less than 2.5 kPa at 20°C, including the following monomers: tetraethyl orthosilicate, pentamethyldisiloxane, hexamethyldisiloxane, hexamethyldisilazane, bis(trimethylsiloxymethylsilane), octamethyltrisiloxane, 1,1,3,3-tetramethyldisiloxane, tetramethyldivinyldisiloxane, vinylpentamethyldisiloxane, dimethoxymethylvinylsilane, 1,3-diethyl-1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,5-divinyl-hexamethyltrisiloxane, 1-vinyl-1,1,3,3-tetramethyldisiloxane, silane, methane, ethane, hexafluoropropylene, hexafluorobutyl acrylate, acrylic acid, and butyl methacrylate. The precursor B is one or more of the organosilane monomers having one or more rings, the relative silicon content in the precursor B is greater than 40%, and the saturated vapor pressure at 20°C is not less than 0.1 kPa, including the following monomers: 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, octamethylcyclotetrasiloxane, 2,4,6,8-tetramethyltetravinylcyclotetrasiloxane, heptamethylcyclotetrasiloxane, 2,4,6,8,10-cyclopentasiloxane, acetoxyheptamethylcyclotetrasiloxane; The precursor C is a linear organosilicon monomer with a main chain of -Si-O-, including the following monomers: pentamethyldisiloxane, hexamethyldisiloxane, bistrimethylsiloxymethylsilane, octamethyltrisiloxane, 1,1,3,3-tetramethyldisiloxane, tetramethyldivinyldisiloxane, vinylpentamethyldisiloxane, 1,3-diethyl-1,1,3,3-tetramethyldisiloxane, 1-allyl-1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,5-divinyl-hexamethyltrisiloxane, 1-vinyl-1,1,3,3-tetramethyldisiloxane, and 1,3-di(chloromethyl)-1,1,3,3-tetramethyldisiloxane.

7. The method for preparing the transparent, fluorine-free, hydrophobic, and antifouling coating as described in claim 5, characterized in that: The auxiliary reaction gases D and E are one or a mixture of two or more of Ar, O2, N2, H2O, H2O2, and H2.

8. The method for preparing the transparent, fluorine-free, hydrophobic, and antifouling coating as described in claim 5, characterized in that: The time interval between shutting off auxiliary reaction gas D, opening precursor C, and shutting off precursor B is 10~300s. The deposition time from shutting off precursor B to the end of deposition is 60~900s.

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