CN111825985A

CN111825985A - Flexible film of bionic air cavity structure and preparation method thereof

Info

Publication number: CN111825985A
Application number: CN202010658121.0A
Authority: CN
Inventors: 薛培宏; 刘皓
Original assignee: Dalian Maritime University
Current assignee: Dalian Maritime University
Priority date: 2020-07-09
Filing date: 2020-07-09
Publication date: 2020-10-27
Anticipated expiration: 2040-07-09
Also published as: CN111825985B

Abstract

The invention provides a flexible film, wherein air cavities are arranged on the surface of the film, the air cavities are of a bombyx elater-like structure, the air cavities are distributed on the surface of the flexible film in a single-layer close-packed array form, and the size of the air cavities is micro-nano; the micro-nano structure of the flexible film provided by the invention is in two-dimensional scale, and can show dynamic change of wettability under tensile stimulation, so that the application flexibility is increased. The flexible film provided by the invention is prepared by utilizing a soft lithography principle, the preparation method is simple, quick and efficient, and a target structure sample can be quickly prepared.

Description

Flexible film of bionic air cavity structure and preparation method thereof

Technical Field

The invention belongs to the technical field of material science, and particularly relates to a method for preparing a micro-nano structure array functional material with an air pocket structure on the surface of the material by utilizing a soft lithography principle.

Background

The research on the material performance mainly centers on the relationship among the material, the structure and the performance of the material, and with the progress of the detection technology, people find that the micro-nano structure on the surface of the material makes the material obtain new characteristics different from the macro-scale structure except the macroscopic-scale structure. Therefore, the construction of micro-nano-scale structures on the surface of materials and the study of their properties are one of the important issues in the field of material science at present. By developing micro-nano processing technologies of different material surfaces, people realize the diversification of micro-nano structures and properties of the material surfaces and apply the micro-nano structures and the properties to various fields in life.

The stable presence of gas between the liquid and the microstructure on the solid surface is an accelerator to achieve superhydrophobicity of the surface. The increase in gas fraction enhances the hydrophobicity of the rough surface and thus is more suitable for the Cassie-Baxter model, which makes the surface more susceptible to super-hydrophobicity or super-oleophobicity. In nature, the mushroom-like surface structure of the tail beetles has attracted a great deal of attention from scientists. The inwardly concave configuration prevents the penetration of water and oil, thereby providing oxygen to the insect for continued survival under particular conditions. Inspired by the tail beetles, obtaining a high proportion of the gaseous fraction and maintaining its stability is an effective way to construct superhydrophobic surfaces. However, in scientific research, the natural structure has its limitations. Therefore, it is very meaningful to develop a simple method for obtaining a superhydrophobic surface by combining a bionic micro-nano structure.

Disclosure of Invention

The invention provides a method for preparing a micro-nano structure array functional material with an air pocket structure on the surface of the material by utilizing the soft lithography principle, which is simple, rapid and efficient.

The technical scheme of the invention is as follows:

in one aspect, the present invention provides a flexible film having air pockets on a surface of the film; the air pocket is a springtail-imitating structure, namely a cavity structure with a small opening and a large inner cavity formed by inwards recessing the surface of the film, namely, the width of the opening is smaller than the maximum width inside the cavity in any cross section of the cavity in the vertical direction (the vertical direction is a direction perpendicular to the plane of the film).

Preferably, the air pockets are distributed on the surface of the flexible film in a monolayer close-packed array; the air cavity size is on the micro-nanometer scale.

Preferably, the monolayer close-packed array is monolayer hexagonal close-packed; the diameter of the air cavity is 1-2 mu m; preferably 2 μm.

In another aspect, the present invention provides a method for preparing the above flexible film, including the steps of:

step a: preparing a monolayer close-packed polymer microsphere array on a hydrophilic substrate;

step b: performing soft lithography on the array of microspheres with polydimethylsiloxane;

step c: and separating the polydimethylsiloxane from the substrate to obtain the flexible film with the bionic air cavity structure.

Preferably, the step a includes the steps of: dispersing the polymer microspheres subjected to hydrophobic treatment in a mixed solution of ethanol and water to obtain a dispersion liquid of the polymer microspheres; filling deionized water into the culture dish, dripping the dispersion liquid onto an air-deionized water interface in the culture dish, standing for 10-30 s, and dripping a water solution of a surfactant along the side wall of the culture dish to enable the polymer microspheres to be tightly stacked into a single layer; extending the hydrophilic substrate below the water surface, paving the hydrophilic substrate below a single-layer microsphere, slowly lifting the hydrophilic substrate upwards from the lower part of the single-layer microsphere, and then placing the hydrophilic substrate on an inclined plane for natural drying, thereby obtaining a single-layer closely-packed polymer microsphere array on the hydrophilic substrate;

the hydrophobic treatment comprises the following steps: using ethanol and water in a volume ratio of 1: 1, performing centrifugal cleaning to remove the surfactant in the original polymer microsphere solution;

the volume ratio of ethanol to water in the mixed solution is 1: 1; the dosage of the mixed solution is 5-20 mL; the concentration of the dispersion liquid is 1-20 wt%; dropwise adding the dispersion liquid through a disposable syringe; the dosage of the dispersion liquid is 0.1-1.0 mL; the dosage of the surfactant aqueous solution is 50-200 mu L, and the concentration is 5-10 wt%; the hydrophilic substrate is made of a material different from that of the polymer microspheres.

Preferably, the step b comprises the steps of: b, placing the microsphere array prepared in the step a into a culture dish, fixing the bottom of the culture dish, mixing polydimethylsiloxane and a curing agent, vacuumizing to remove bubbles, injecting the obtained mixture into the culture dish, curing at the temperature of 40-80 ℃ for 2-6 hours by taking the microsphere array as a mask, and separating the polydimethylsiloxane from the mask after the curing is finished;

the step c comprises the following steps: b, placing the polydimethylsiloxane prepared in the step b in a good solvent of a microsphere mask, performing ultrasonic treatment for 1-20 min by using an ultrasonic instrument, taking out the polydimethylsiloxane, washing the polydimethylsiloxane for 2-3 times by using deionized water, and drying the polydimethylsiloxane by using nitrogen gas to obtain a micro-nano structure array on the bottom surface of the polydimethylsiloxane so as to obtain the flexible film with the bionic air cavity structure; the mass ratio of the polydimethylsiloxane to the curing agent is 10: 1.

preferably, the polymeric microspheres are polystyrene microspheres; the hydrophilic substrate is hydroxylated quartz or silicon wafer.

Preferably, the surfactant is sodium dodecyl sulfate or sodium dodecyl benzene sulfonate.

Preferably, the good solvent for the microsphere mask is toluene.

On the other hand, the flexible film of the bionic air cavity structure provided by the invention can be applied to lyophobic, anti-icing and anti-fog materials of microfluidic devices.

The flexible film provided by the invention can generate reversible change of wetting property under certain stretching.

Advantageous effects

1. The micro-nano structure of the flexible film provided by the invention is in two-dimensional scale, and can show dynamic change of wettability under tensile stimulation, so that the flexibility of the flexible film in the field of microelectronic devices and application is improved.

2. The method is simple, fast and efficient, and can be used for rapidly preparing the target structural sample.

Drawings

FIG. 1: the preparation process schematic diagram of the flexible film of the bionic air cavity structure;

step a is to prepare a single-layer hexagonal close-packed polystyrene microsphere array on a substrate; step b, performing soft lithography on the monolayer hexagonal close-packed microsphere array; and step c, removing the polymer from the substrate to obtain the flexible film with the bionic air cavity structure.

FIG. 2: scanning electron microscope top and side views of the polydimethylsiloxane films prepared in the examples, with a 2 μm scale.

FIG. 3: based on the wettability chart of the polydimethylsiloxane film prepared in the example, 2 mu L of water and dichloromethane are taken by a syringe to characterize the wettability of the surface of the film, the wetting angle of the water on the surface of the film reaches 150 degrees, and the wetting angle of the dichloromethane on the surface of the film reaches 130 degrees.

FIG. 4: based on the state diagrams (a-c) of the wetting behavior of the polydimethylsiloxane films prepared in the examples, which change the wetting behavior of water by tensile stimulation, a) a schematic diagram of the wettability of the films to water by stretching; b) a chart of the wettability of the film to water in an unstretched state; c) the wettability of the film to water in the stretched state.

FIG. 5: comparative antifog testing of the structured polydimethylsiloxane films prepared in the examples and the untreated polydimethylsiloxane films;

FIG. 6: hydrophobicity comparison of structured polydimethylsiloxane films prepared in the examples and untreated polydimethylsiloxane films.

Detailed Description

The following description is only a preferred embodiment of the present invention, and is not intended to limit the technical scope of the present invention in any way. Any simple modification, equivalent change and modification of the above embodiments according to the technical spirit of the present invention fall within the scope of the present invention. The raw materials used in the following examples are all conventional products which can be obtained commercially.

Example 1

(1) Preparation of hydrophilic silicon wafer

The used silicon wafer is a monocrystalline silicon wafer, the silicon wafer is cut to be 2cm long and 2cm wide by a glass cutter, mixed solution (volume ratio is 7: 3) of concentrated sulfuric acid (mass fraction is 98%) and hydrogen peroxide (mass fraction is 30%) is put into the silicon wafer, the silicon wafer is heated to 80 ℃ in a water bath, and the silicon wafer is kept for 5 hours, so that the hydrophilic silicon wafer is obtained; and then pouring the mixed solution into a waste liquid bottle, repeatedly washing the obtained hydrophilic silicon wafer with deionized water for 5 times, and storing the hydrophilic silicon wafer in the deionized water for later use.

(2) Preparation of hydrophobic polystyrene microspheres

Taking 10mL of ethanol dispersion of polystyrene colloidal microspheres (microsphere diameter is 1 mu m) with concentration of 10 wt%, and mixing the ethanol dispersion with water according to the volume ratio of ethanol to water of 1: 1 is subjected to 15 centrifugal washes to remove the surfactant from the stock solution, and finally dispersed in 10mL of ethanol to water at a volume ratio of 1: 1, obtaining the dispersion liquid of the ethanol and the water of the polystyrene colloidal microspheres, wherein the concentration is 5 weight percent, and the surface properties of the polystyrene colloidal microspheres are hydrophobic.

(3) Preparation of hexagonal close-packed polystyrene microsphere array

0.2mL of the ethanol-water dispersion of the hydrophobic polystyrene colloidal microspheres of 1 μm diameter prepared in example 2 was slowly dropped onto the air-deionized water interface of a petri dish by means of a disposable syringe, left to stand for a while, and 50 μ L of a 10 wt% aqueous solution of sodium dodecyl sulfate was added along one side of the petri dish, whereupon the polystyrene colloidal microspheres formed a hexagonal close-packed monolayer. And (2) taking the hydrophilic silicon wafer prepared in the step (1) as a substrate, extending into the position below the water surface, slowly lifting upwards from the position below the compact single-layer microspheres, placing on an inclined plane, and naturally drying, thereby obtaining a single-layer compact-packed polystyrene colloidal crystal on the silicon wafer.

(4) Preparation of polydimethylsiloxane film capable of changing wetting behavior of water through stretching

And (4) placing the single-layer hexagonal close-packed polystyrene microsphere array prepared in the step (3) into a culture dish, and fixing the bottom. Mixing polydimethylsiloxane and a curing agent in a ratio of 10 to 1, vacuumizing to remove bubbles after mixing, injecting the obtained mixture into a culture dish, and curing at 40 ℃ for 6 hours by taking a polystyrene microsphere array of a sample as a mask. After curing, the polydimethylsiloxane was detached from the sample. And placing the prepared sample in a toluene solvent, carrying out ultrasonic treatment on the sample in the solvent for 20min by using an ultrasonic instrument, removing the residual microsphere mask on the surface of the sample, taking out the sample, washing the sample for 2 times by using deionized water, and drying the sample by using nitrogen gas, thereby preparing the polydimethylsiloxane film capable of changing the wetting behavior of water by stretching.

Fig. 2 is a scanning electron microscope image of the film. As shown, the biomimetic air pocket structures are closely arranged in a hexagonal packing on the polydimethylsiloxane film. As can be seen from the side view, the openings at the top end are small, creating a unique air pocket structure. This structure helps the surface to get a higher gas fraction, increasing the hydrophobicity of the material surface.

FIG. 3 shows the results of the hydrophobicity and oleophobicity tests of the resulting films. As shown in the figure, the contact angle of the polydimethylsiloxane film with the bionic air cavity structure to water reaches 150 degrees, the contact angle to dichloromethane reaches 130 degrees, and super-hydrophobicity and super-oleophobicity are realized.

Fig. 4 shows the change in wettability of the film under a tensile stimulus. In the stretched state, the contact angle of the film surface to water is changed from 150 degrees to 130 degrees, and the controllable wettability change is realized.

Comparative example 1

As shown in fig. 5, the antifogging test was performed on the structured polydimethylsiloxane film and the untreated polydimethylsiloxane film, and the water vapor adhesion on the structured film was very small while the untreated polydimethylsiloxane film was covered with water vapor, which verifies that the bionic cavitation structure enhances the antifogging property of the polydimethylsiloxane film.

Comparative example 2

As shown in FIG. 6, the contact angle of water on the untreated polydimethylsiloxane film is only 110 degrees, while the contact angle of water on the surface of the structured polydimethylsiloxane film can reach 150 degrees, which confirms that the bionic cavitation structure increases the hydrophobicity.

Claims

1. A flexible film, wherein the film surface has air pockets; the air pocket is of a structure imitating a bombyx elater.

2. The flexible film of claim 1, wherein said air pockets are distributed on said flexible film surface in a monolayer close-packed array; the air cavity size is on the micro-nanometer scale.

3. The flexible film of claim 2, wherein the monolayer close-packed array is monolayer hexagonal close-packed; the diameter of the air cavity is 1-2 μm.

4. A method of making a flexible film according to any one of claims 1 to 3, comprising the steps of:

5. The production method according to claim 4,

the step a comprises the following steps: dispersing the polymer microspheres subjected to hydrophobic treatment in a mixed solution of ethanol and water to obtain a dispersion liquid of the polymer microspheres; filling deionized water into the culture dish, dripping the dispersion liquid onto an air-deionized water interface in the culture dish, standing for 10-30 s, and dripping a water solution of a surfactant along the side wall of the culture dish to enable the polymer microspheres to be tightly stacked into a single layer; extending the hydrophilic substrate below the water surface, paving the hydrophilic substrate below a single-layer microsphere, lifting the hydrophilic substrate from the lower part of the single-layer microsphere, and placing the hydrophilic substrate on an inclined plane for natural drying, so that a single-layer closely-packed polymer microsphere array is obtained on the hydrophilic substrate;

6. The production method according to claim 4,

the step b comprises the following steps: b, placing the microsphere array prepared in the step a into a culture dish, fixing the bottom of the culture dish, mixing polydimethylsiloxane and a curing agent, vacuumizing to remove bubbles, injecting the obtained mixture into the culture dish, curing at the temperature of 40-80 ℃ for 2-6 hours by taking the microsphere array as a mask, and separating the polydimethylsiloxane from the mask after the curing is finished;

7. the method for preparing the flexible film of the bionic cavitation structure according to claim 4, characterized in that: the polymer microspheres are polystyrene microspheres; the hydrophilic substrate is hydroxylated quartz or silicon wafer.

8. The method for preparing the flexible film of the bionic cavitation structure according to claim 5, characterized in that: the surfactant is sodium dodecyl sulfate or sodium dodecyl benzene sulfonate.

9. The method for preparing a flexible film of a bionic cavitation structure according to claim 6, characterized in that: the good solvent of the microsphere mask is toluene.

10. Use of a flexible membrane of biomimetic cavitation structure according to any of claims 1-3, characterized in that: the flexible film is applied to lyophobic, anti-icing and anti-fog materials of microfluidic devices.