A pressure-induced wetting state and morphology controllable superhydrophobic silicone rubber elastomer and its preparation method

Abstract

This invention belongs to the field of functional polymer materials, and particularly relates to a pressure-induced wetting state and morphology-controllable superhydrophobic silicone rubber elastomer and its preparation method. The preparation method includes the following steps: dispersing hydrophobic nano-silica powder in an elastic prepolymer to obtain a premix; adding a reactant to the premix and mixing to obtain a reaction solution; and contacting the reaction solution with a structure having a rough surface and curing it. This invention fills nano-silica modified with KH570 and KH550 silanes into polydimethylsiloxane, and constructs a regular rough structure on its surface using a screen, thus preparing a pressure-induced wetting state and morphology-controllable superhydrophobic silicone rubber elastomer.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials, and particularly relates to a pressure-induced wettable state and morphology controllable superhydrophobic silicone rubber elastomer and its preparation method. Background Technology

[0002] Controllable superhydrophobic surfaces have attracted increasing attention due to their wide range of applications in droplet transport, water droplet collection and acquisition, biomedical analysis equipment, droplet reactions, water condensation, and microfluidic devices. For example, in biomedical devices, the contact angle of the medical device surface has a crucial impact on determining cell adhesion and growth; in droplet transport, droplets can be moved by moving superhydrophobic surfaces with high adhesion, and controllable adhesion is key to directional droplet transport.

[0003] Existing research indicates that superhydrophobic surfaces with different rough structures can exhibit different adhesion effects, such as the lotus leaf effect and the rose petal effect. The lotus leaf effect demonstrates very weak water adhesion; water droplets roll easily in a spherical shape on a lotus leaf-like surface, exhibiting a "repulsive" phenomenon towards water. This can be explained by the Cassie-Baxter model, and surfaces with the lotus leaf effect can be applied in areas such as self-cleaning and underwater drag reduction. Conversely, the rose petal effect exhibits high water adhesion and water-capturing properties. It can act as a "grip" to control and transport tiny water droplets, and the Wenzel model can well explain the rose petal effect. The wettability and adhesion properties of the same superhydrophobic surface are fixed and only conform to one of the Wenzel model, the Cassie-Baxter model, or other models, limiting its applicability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a pressure-induced wetted state and a superhydrophobic silicone rubber elastomer with controllable morphology. This method involves filling hydrophobic nano-silica into polydimethylsiloxane and preparing a pressure-induced wetted state and a superhydrophobic silicone rubber elastomer with controllable morphology by contacting the structure with a rough surface.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a pressure-induced wetted state and morphology-controllable superhydrophobic silicone rubber elastomer, comprising the following steps: dispersing hydrophobic nano-silica powder in an elastic prepolymer to obtain a premixed liquid; adding a reactant to the premixed liquid and mixing to obtain a reaction liquid; and contacting the reaction liquid with a structure having a rough surface and curing it.

[0007] According to an embodiment of the present invention, the hydrophobic nano silica is selected from nano silica whose surface has been modified by epoxy resin, alkyl, or fluoroalkyl. For example, the hydrophobic nano silica is selected from silica whose surface has been modified by KH570 or KH550 silane coupling agents.

[0008] According to an embodiment of the present invention, the elastic prepolymer is selected from at least one of vinyl silicone oil, ethoxy silicone oil, and hydrogen-containing silicone oil, for example, polydimethylsiloxane.

[0009] According to an embodiment of the present invention, the hydrophobic nano-silica particles have a particle size of 50-300 nm, preferably 100-200 nm.

[0010] According to an embodiment of the present invention, the reactant is at least one selected from the crosslinking agents methyltrimethoxysilane, aminopropyltriethoxysilane, tetraethoxysilane, and methyltriethoxysilane.

[0011] According to an embodiment of the present invention, the mass ratio of the elastic prepolymer to the modified nano-silica is 100:(10-80), preferably 100:(20-60), and more preferably 100:(30-50).

[0012] According to an embodiment of the present invention, the mass ratio of the elastic prepolymer to the reactant is 10:(0.5-2), preferably 10:(1-1.5).

[0013] According to an embodiment of the present invention, the structure with a rough surface refers to a structure that, after contact with the reaction liquid and curing, enables the cured elastomer surface to form a periodic protrusion structure.

[0014] According to an embodiment of the present invention, the structure with a rough surface is a mesh structure or a laser-etched mesh template. The mesh structure is selected from a wire mesh with a size of 500 to 3000 meshes. Preferably, the mesh structure is selected from a wire mesh with a size of 1000 to 2000 meshes. More preferably, the wire mesh is stainless steel or nylon wire mesh.

[0015] According to an embodiment of the present invention, the laser etching template is a grid template with a smooth steel plate as the base and a laser spot of 0.5 to 5 micrometers. Preferably, the laser etching grid template is selected from a grid template with a laser spot of 1 to 3 micrometers.

[0016] According to an embodiment of the present invention, before the reaction liquid is brought into contact with the structure having a rough surface, the following step is further included: applying a release agent to the surface of the structure having a rough surface and drying it.

[0017] According to an embodiment of the present invention, before applying the release agent to the surface of the structure with a rough surface, the method further includes the following steps: cleaning and drying the structure with a rough surface. According to an embodiment of the present invention, contacting and curing the reaction solution with the structure with a rough surface includes the following steps: placing the structure with a rough surface inside a mold, and placing the reaction solution into the mold for curing.

[0018] According to an embodiment of the present invention, the curing of the reaction solution in a mold includes the following steps: first, storing the reaction solution under vacuum conditions, and then drying and curing it at a temperature of 30 to 60°C.

[0019] According to an embodiment of the present invention, the drying and curing time is 2 to 6 hours, preferably 3 to 5 hours.

[0020] According to an embodiment of the present invention, the drying and curing are carried out in a vacuum drying oven.

[0021] According to an embodiment of the present invention, storing the reaction solution under vacuum conditions includes the following steps: evacuating the reaction solution until the surface is level, uniform, and free of bubbles, maintaining the vacuum state for 1-5 minutes, and then releasing the vacuum.

[0022] Secondly, the present invention provides a pressure-induced wettable state and morphology-controllable superhydrophobic silicone rubber elastomer prepared by the above method. The surface of the elastomer has continuous periodic protrusions of micro-nano structure. When the surface of the elastomer is subjected to pressure, the surface of the elastomer changes from the Cassie-Baxter state to the Wenzel state.

[0023] According to an embodiment of the present invention, the periodic protrusion is a triangular protrusion and / or a trapezoidal protrusion.

[0024] According to an embodiment of the present invention, the contact angle of the elastomer is greater than 150° and the roll-off angle is less than 10°.

[0025] Beneficial effects

[0026] 1. This invention uses a mechanical blending method to mechanically blend silane-modified nano-silica into polydimethylsiloxane. Both the silane-modified nano-silica and PDMS are low surface energy materials with good compatibility. The organic and inorganic phases are mainly bonded through covalent bonds. Simultaneously, this invention constructs the surface morphology of the elastomer by curing the reaction solution after contacting wire meshes of different finenesses, thus preparing a morphology-controllable SiO2 / PDMS elastomer. This elastomer exhibits a pressure-induced wetting state. The preparation method of this invention is simple, the raw materials are inexpensive and readily available, and it has good application prospects.

[0027] 2. The pressure-induced wettability of the silicone rubber elastomer prepared by this invention is controlled by the morphology of the elastomer surface. By using wire meshes of different fineness, the morphology can be designed in a controllable manner, thereby achieving the purpose of controllable wettability. At the same time, the silicone rubber elastomer prepared by this invention can change from the Cassie-Baxter state to the Wenzel state under external pressure, thereby achieving control over surface adhesion and wettability to handle water.

[0028] 3. This invention designs different rough structures by using wire meshes of different fineness. The wire mesh is placed at the bottom of the mold and then the reaction liquid is poured in for curing. Alternatively, the wire mesh can be attached to the surface of the reaction liquid for curing. The operation is convenient and the cost is low. Attached Figure Description

[0029] Figure 1 These are scanning electron microscope (SEM) images of different morphologies designed on the surface of an elastomer using screens of different fineness in Embodiment 1 of this invention. Figure 1 The image above shows the elastomer surface corresponding to an 800-mesh wire mesh. Figure 1 Below is the elastomer surface corresponding to a 1500 mesh wire mesh.

[0030] Figure 2 This is a graph showing the relationship between the contact angle and roll-off angle of the elastomers prepared under different SiO2 contents and screen printing conditions in Example 1.

[0031] Figure 3 This is a test diagram of the wear resistance of the elastomer prepared in Example 1.

[0032] Figure 4 This is a diagram of the transport of elastomer droplets prepared in Example 1. Detailed Implementation

[0033] The preparation method and application of the superhydrophobic silicone rubber elastomer of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0034] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0035] The prepolymer used in the following examples is a vinyl silicone oil component, and the nano silica is KH570 and KH550 silane-modified nano silica, produced by Ruijiang New Materials Co., Ltd.

[0036] Example 1

[0037] (1) Preparation of nano-SiO2 / PDMS reaction solution

[0038] Weigh 1.0 g of PDMS and 0.6 g of SiO2 powder with a particle size of 200 nm modified by KH570 and KH550 silanes into a beaker. Stir thoroughly in a mechanical stirrer. Thorough stirring means that the mixture in the beaker is smooth and free of particles. The stirring time is set according to actual needs, for example, 1 hour. If thorough stirring is not achieved after 1 hour, the stirring time can be increased appropriately. After stirring is complete, add 0.1 g of methyltrimethoxysilane reactant to the mixture, and then continue stirring for 3 minutes to obtain the reaction solution.

[0039] During stirring, the 1500 mesh and 800 mesh wire meshes were rinsed with anhydrous ethanol and placed in a DNE vacuum drying oven at 50°C for 5 minutes to dry the moisture. The wire meshes were then picked up with tweezers and a release agent was sprayed evenly onto the dried wire mesh surface. The wire meshes were then placed in a DNE vacuum drying oven at 50°C to dry further, thus obtaining the template.

[0040] (2) Preparation of nano-SiO2 / PDMS elastomer

[0041] Place the completely dried screen template at the bottom of the plastic mold, then pour the thoroughly stirred reaction solution into the plastic mold. Place the mold in a 2XZ(C) type rotary vane vacuum pump and evacuate until the surface of the reaction solution is level, uniform, and free of bubbles. Maintain the vacuum for 3 minutes, then release the vacuum. Remove the mold and place it in a DNE vacuum drying oven at 50℃ for at least 4 hours until fully cured to obtain the elastomer. Remove the cured elastomer from the mold, peel off the screen, and obtain the superhydrophobic elastomer samples (superhydrophobic elastomers corresponding to 1500 mesh and 800 mesh screens, respectively).

[0042] (3) Observation of morphology using scanning electron microscopy

[0043] Superhydrophobic elastomer samples corresponding to 800-mesh and 1500-mesh screens were cut to a suitable size (2.0cm × 2.0cm). After being sprayed with gold on the sample surface for 130 seconds using an ETD-800 gold sprayer, the cross-sectional morphology of the samples was observed using a Vega 3SBH scanning electron microscope.

[0044] See Figure 1 The upper part shows the sample corresponding to an 800-mesh screen. The morphology of the prepared sample exhibits a regular, inverted trapezoidal shape; see also... Figure 1 The lower part shows the sample corresponding to the 1500 mesh screen. The prepared sample exhibits a regular triangle shape. It can be seen that this embodiment prepared superhydrophobic elastomers with different surface morphologies by using screens of different fineness. That is, by using screens or other structures to control the surface of the elastomer, the purpose of morphology design can be achieved.

[0045] (4) Superhydrophobicity test

[0046] See Figure 2 As shown, the contact angle and roll-off angle of superhydrophobic elastomers prepared under different SiO2 contents, with and without screen (the preparation method is the same as in steps (1)-(2), the difference being the SiO2 content and screen) were tested.

[0047] In this embodiment, the contact angle and roll-off angle of the superhydrophobic elastomer were measured using an SDC-350 contact angle meter. The prepared superhydrophobic elastomer sample was placed on a table, and the contact angle was measured using a 2 μL water droplet and the roll-off angle was measured using a 5 μL water droplet. The data were recorded as shown in Figure 2. As the amount of SiO2 powder added increased, the hydrophobicity of the corresponding superhydrophobic elastomer also increased. The contact angle was the largest when the amount of SiO2 powder added reached 60%.

[0048] The contact angle of the superhydrophobic elastomer can be greater than 150°, while the roll-off angle is less than 10°, indicating that the superhydrophobic elastomer prepared by this invention has good hydrophobic effect. At the same time, the sample without using a wire mesh to construct the morphology cannot achieve the superhydrophobic effect. It can be seen that the superhydrophobic performance is the result of the synergistic effect of SiO2 powder content and wire mesh.

[0049] (5) Friction resistance test

[0050] See Figure 3 As shown, a superhydrophobic elastomer sample (2.0cm × 2.0cm) with a SiO2 content of 60% was prepared using a 1500-mesh screen. A 50g weight was placed on top of the sample to apply pressure. The superhydrophobic side of the sample was placed on sandpaper, with a ruler parallel to the sample. Wearing gloves, the sample was dragged 50cm across the sandpaper using tweezers. The contact angle and roll-off angle were then measured using an SDC-350 contact angle meter. This process was repeated seven times. Figure 3 As shown in Figure a, the friction resistance of the sample was observed and analyzed. When the friction distance was within 1.5 meters, the surface of the superhydrophobic elastomer sample could still maintain a superhydrophobic state with a contact angle greater than 150° and a roll-off angle less than 10°. Therefore, the superhydrophobic elastomer sample has good wear resistance.

[0051] (6) Tests for controllable pressure-induced wettability of materials

[0052] Observation was conducted using an SDC-350 contact angle measuring instrument and camera. An elastomer with 60% SiO2 content prepared using an 800-mesh screen was placed at the bottom, and an elastomer with 60% SiO2 content prepared using a 1500-mesh screen was placed at the top. 5 μL of deionized water was dropped onto the surface of the 800-mesh elastomer. The two elastomers were slowly brought into contact. When the 1500-mesh elastomer pressed a 5 μL water droplet downwards by 2 mm vertically for 10 seconds, the droplet was adhered to the 1500-mesh elastomer. This indicates that both elastomers possess good hydrophobic properties. Furthermore, under pressure, the wettability of the elastomer prepared using the 1500-mesh screen is greater than that of the 800-mesh elastomer. This demonstrates that the surface wettability of the material can be adjusted by selecting different mesh fineness.

[0053] Example 2

[0054] (1) Preparation of nano-SiO2 / PDMS reaction solution

[0055] Weigh 1.0g of PDMS and 0.1g of unmodified 200nm SiO2 powder into a beaker and stir thoroughly in a mechanical stirrer. Thorough stirring means that the mixture in the beaker is smooth and free of particles. The stirring time can be 1 hour. If the stirring effect is not achieved after 1 hour, the stirring time can be increased appropriately. After stirring, add 0.1g of methyltrimethoxysilane reactant to the system and continue stirring for 3 minutes to obtain the reaction solution.

[0056] During the stirring process, the 1500 mesh screen is rinsed clean with anhydrous ethanol and placed in a 50℃ DNE vacuum drying oven for 5 minutes to dry the moisture. The screen is then picked up with tweezers, and a release agent is evenly sprayed onto the surface. It is then placed in a 50℃ DNE vacuum drying oven to dry further, thus obtaining the template.

[0057] (2) Preparation of nano-SiO2 / PDMS elastomer

[0058] Place the completely dried screen at the bottom of the plastic mold, then pour the thoroughly stirred reaction liquid into the plastic mold. Place it in a 2XZ(C) type rotary vane vacuum pump and evacuate until the surface of the mixed adhesive is level, uniform, and free of bubbles. Maintain the vacuum state for 3 minutes, then release the vacuum. Take it out and place it in a DNE vacuum drying oven at 50℃ for more than 4 hours until it is completely cured. Remove the cured elastomer from the mold, peel off the screen, and you will get the superhydrophobic elastomer.

[0059] Example 3

[0060] (1) Preparation of nano-SiO2 / PDMS reaction solution

[0061] Weigh 1.0g of PDMS and 0.2g of KH570 and KH550 silane-modified 200nm SiO2 powder into a beaker and stir thoroughly in a mechanical stirrer. Thorough stirring means that the mixture in the beaker is smooth and free of particles. The stirring time can be 1 hour. If thorough stirring is not achieved after 1 hour, the stirring time can be increased appropriately. After stirring, add 0.1g of methyltrimethoxysilane reactant and continue stirring for 3 minutes to obtain the reaction solution. During stirring, wash the 800-mesh screen with anhydrous ethanol and place it in a 50℃ DNE vacuum drying oven for 5 minutes to dry the moisture, obtaining the dried screen.

[0062] (2) Preparation of nano-SiO2 / PDMS elastomer

[0063] Place the completely dried screen at the bottom of the plastic mold, then pour the thoroughly stirred reaction liquid into the plastic mold. Place it in a 2XZ(C) type rotary vane vacuum pump and evacuate until the surface of the mixed adhesive is level, uniform, and free of bubbles. Maintain the vacuum state for 3 minutes, then release the vacuum. Take it out and place it in a DNE vacuum drying oven at 50℃ for more than 4 hours until it is completely cured. Remove the cured elastomer from the mold, peel off the screen, and you will get the superhydrophobic elastomer.

[0064] Example 4

[0065] (1) Preparation of nano-SiO2 / PDMS reaction solution

[0066] Weigh 1.0g of PDMS and 0.3g of KH570 and KH550 silane-modified 200nm SiO2 powder into a beaker and stir thoroughly in a mechanical stirrer. Thorough stirring means that the mixture in the beaker is smooth and free of particles. The stirring time can be 1 hour. If thorough stirring is not achieved after 1 hour, the stirring time can be increased appropriately. After stirring, add 0.1g of methyltrimethoxysilane reactant and continue stirring for 3 minutes to obtain the reaction solution. During stirring, wash the 1500 mesh screen with anhydrous ethanol and place it in a 50℃ DNE vacuum drying oven for 5 minutes to dry the moisture. Use tweezers to pick up the screen and spray a release agent evenly on the surface to obtain the template.

[0067] (2) Preparation of nano-SiO2 / PDM elastomers

[0068] Place the partially dried screen at the bottom of a plastic mold, then pour the thoroughly stirred reaction solution into the mold. Place the mold in a 2XZ(C) type rotary vane vacuum pump and evacuate until the surface of the mixed adhesive is level, uniform, and free of air bubbles. Maintain the vacuum for 3 minutes, then release the vacuum. Remove the mold and place it in a DNE vacuum drying oven at 50℃ for at least 4 hours until fully cured. Remove the cured elastomer from the mold, peel off the screen, and you will obtain the superhydrophobic elastomer.

[0069] Analysis example

[0070] The samples prepared in Example 2 and Example 1 were analyzed. In Example 2, unmodified nano-silica without KH570 or KH550 silane modification was used as the reactant. Since the surface of unmodified nano-silica is a hydrophilic material, the superhydrophobic elastomer will decrease in hydrophobicity after prolonged contact with water and eventually transform into a hydrophilic material.

[0071] Analyzing the samples from Example 3 and Example 1, the elastomer obtained in Example 3 without using a release agent on the screen surface did not achieve a superhydrophobic effect. This is because when no release agent is used, after the reaction liquid comes into contact with and solidifies the screen, the rough structure on the surface of the elastomer is difficult to detach from the screen surface. As a result, during the process of peeling off the screen, the rough structure on the surface of the elastomer adheres to the screen, thereby destroying the micro-nano structure and thus failing to achieve a superhydrophobic effect.

[0072] Analysis of the samples from Example 4 and Example 1 shows that when the release agent on the screen surface of Example 4 was used directly before it was completely dry, the elastomer surface could not achieve a superhydrophobic effect. This is because when the release agent is not completely dry, the reaction liquid is directly applied to the screen surface, which prevents the reaction liquid from making good contact with the screen. As a result, the elastomer obtained after curing cannot replicate the morphology of the screen well, which reduces the roughness and thus fails to achieve the purpose of superhydrophobicity.

[0073] The specific embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above exemplary embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a pressure-induced wetted state and morphology controllable superhydrophobic silicone rubber elastomer, characterized in that, The process includes the following steps: dispersing hydrophobic nano-silica powder in an elastic prepolymer to obtain a premix; adding a reactant to the premix and mixing to obtain a reaction solution; and contacting the reaction solution with a structure having a rough surface and curing it. The hydrophobic nano silica is selected from silica whose surface has been modified by KH570 silane coupling agent or KH550 silane coupling agent, and the particle size of the hydrophobic nano silica is 50~300 nm. The elastic prepolymer is selected from vinyl silicone oil, and the reactant is at least one of methyltrimethoxysilane, tetraethoxysilane, and methyltriethoxysilane. The structure with a rough surface is a mesh structure or a laser-etched mesh template, wherein the mesh structure is selected from a wire mesh with a size of 500 to 3000 mesh. Before the reaction solution is brought into contact with the structure with a rough surface, the following steps are also included: cleaning and drying the structure with a rough surface, and applying a release agent to the surface of the structure with a rough surface and drying it. The process of contacting and curing the reaction solution with a structure having a rough surface includes the following steps: placing the structure having a rough surface inside a mold, and then placing the reaction solution into the mold for curing. The curing process of placing the reaction solution into a mold includes the following steps: first, storing the reaction solution under vacuum conditions, and then drying and curing it at a temperature of 30~60℃ for 2~6 hours; The process of storing the reaction solution under vacuum includes the following steps: evacuate the reaction solution until the surface is level, uniform, and free of bubbles, maintain the vacuum state for 1-5 minutes, and then release the vacuum.

2. The method for preparing a pressure-induced wetted state and morphology-controllable superhydrophobic silicone rubber elastomer according to claim 1, characterized in that, The mass ratio of the elastic prepolymer to the modified nano-silica is 100:(10~80).

3. The method for preparing a pressure-induced wetted state and morphology-controllable superhydrophobic silicone rubber elastomer according to claim 2, characterized in that, The mass ratio of the elastic prepolymer to the modified nano-silica is 100:(20~60).

4. The method for preparing a pressure-induced wetted state and morphology-controllable superhydrophobic silicone rubber elastomer according to claim 1, characterized in that, The mass ratio of the elastic prepolymer to the reactant is 10:(0.5~2).

5. The method for preparing a pressure-induced wetted state and morphology-controllable superhydrophobic silicone rubber elastomer according to any one of claims 1-4, characterized in that, The laser-etched mesh template is a mesh template etched with a laser spot of 0.5 to 5 micrometers, with a smooth steel plate as the base.

6. The method for preparing a pressure-induced wetted state and morphology-controllable superhydrophobic silicone rubber elastomer according to claim 5, characterized in that, The laser-etched mesh template is selected from mesh templates etched by laser spot with a size of 1-3 micrometers.

7. The method for preparing a pressure-induced wetted state and morphology-controllable superhydrophobic silicone rubber elastomer according to any one of claims 1-4, characterized in that, The drying and curing time is 3-5 hours.

8. A pressure-induced wettable state and morphology-controllable superhydrophobic silicone rubber elastomer prepared by the preparation method according to any one of claims 1-7, wherein the surface of the elastomer has continuous periodic protrusions of micro-nano structure, and when the surface of the elastomer is subjected to pressure, the surface of the elastomer changes from the Cassie-Baxter state to the Wenzel state, wherein the periodic protrusions are triangular protrusions and / or trapezoidal protrusions, and the contact angle of the elastomer is greater than 150° and the roll-off angle is less than 10°.

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