CN108467282B

CN108467282B - Molecular brush grafted self-cleaning material and preparation method and application thereof

Info

Publication number: CN108467282B
Application number: CN201810236630.7A
Authority: CN
Inventors: 衡利苹; 王璇
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2018-03-21
Filing date: 2018-03-21
Publication date: 2020-08-04
Anticipated expiration: 2038-03-21
Also published as: CN108467282A

Abstract

The invention relates to a self-cleaning material grafted by molecular brushes, which takes a silicon wafer material as a base material, wherein at least one surface of the base material is grafted with polydimethylsiloxane molecular brushes with the thickness of 4.0-4.5 nm; grooves with the width of 0.1-35 mu m and the height of 5-60 nm are uniformly distributed on the surface of the base material, and the polydimethylsiloxane molecular brush is grafted on the surface of the base material. The invention combines abrasive material grinding and molecular brush grafting to prepare the self-cleaning material with excellent anisotropy in air and underwater. The self-cleaning material disclosed by the invention has excellent anisotropic sliding property for various liquid drops, water and bubbles, and has the characteristics of realizing anisotropic self-cleaning in air, realizing bubble transportation with strong underwater stability and the like.

Description

Molecular brush grafted self-cleaning material and preparation method and application thereof

Technical Field

The invention relates to a molecular brush grafted anisotropic interface material, in particular to a molecular brush grafted self-cleaning material and a preparation method and application thereof.

Background

In recent years, a new sliding interface (Angew,2016,128 (1): 252-. Meanwhile, the nature provides a new method and a new way for people to design innovative advanced materials, and in recent years, people develop an anisotropic interface through observation and research on pitcher plant, rice leaves, butterfly wings and the like, and the interface has great application prospects in the fields of microfluidic equipment, lab-on-a-chip, microreactors, resistance reduction, pollution prevention, self-cleaning and the like. The commonly adopted methods for preparing the anisotropy are methods such as laser, replication, photoetching, electroplating and the like, and the defects that special equipment is needed or the adjustment range of the anisotropy is not ideal exist, so that the wide application of the anisotropy is limited. In order to realize the preparation of the anisotropic interface which is simpler and controllable, a new method needs to be developed urgently.

The anisotropic interfaces reported at present mostly realize the sliding property through structural design, chemical treatment or combination with a liquid injection type super-lubricating interface, and the anisotropic interfaces grafted by a new generation of molecular brushes are basically not reported. Aiming at the two problems, the invention provides the method for preparing the anisotropic interface by adopting carborundum abrasive paper with different grain sizes to carry out constant-load directional polishing on the silicon wafer and adopting the latest molecular brush grafting technology to generate the sliding interface, so that the preparation method has the advantages of simplicity, rapidness, larger anisotropy adjusting range, strong stability, wide application to the sliding of various surface tension liquids and the like, and the carborundum abrasive paper can be better applied to the fields of microfluidic equipment, pollution prevention, resistance reduction, self-cleaning and the like.

Disclosure of Invention

The invention aims to provide a molecular brush grafted self-cleaning material, wherein an anisotropic interface is combined with molecular brush grafting, and the self-cleaning material has the characteristics of strong stability and the like compared with the traditional anisotropic interface and is suitable for the sliding of liquids with various surface tensions.

The self-cleaning material takes a silicon wafer material as a base material, and a polydimethylsiloxane molecular brush with the thickness of 4.0-4.5 nm is grafted on at least one surface of the base material;

grooves with the width of 0.1-35 mu m and the height of 5-60 nm are uniformly distributed on the surface of the base material, and the polydimethylsiloxane molecular brush is grafted on the surface of the base material.

I.e., the polydiorganosiloxane molecular brushes will be grafted into the grooves and also into the voids between the grooves.

Preferably, the size of the silicon wafer material can be selected according to practical application; preferably, the silicon wafer material has a length and width of 1-5 cm and 1-5 cm, and more preferably, a length and width of 2cm and 2cm are used.

The invention further provides that the width of the groove is 15-35 mu m, and the height of the groove is 29-60 nm; most preferably, the width of the trench is 13 to 17 μm and the height is 40 to 50 nm.

The invention further provides that the distance between adjacent grooves is 0.1-35 mu m, preferably 15-35 mu m; more preferably 15 μm.

Preferably, the polydimethylsiloxane molecular brush has a thickness of 4.3 ± 0.1 nm.

In the self-cleaning material, in the air, the contact angle value of water drops along the parallel direction ranges from 104.8 degrees to 105.8 degrees, the contact angle of the water drops along the vertical direction is 107.4 degrees to 123.0 degrees, and the self-cleaning material is in a hydrophobic state; the sliding angle in the parallel direction ranged from 15 to 18 (the sliding angle of the drops was tested with 5. mu.l drops as an example).

Wherein, when the width of the groove is 13 to 17 μm, the obtained cleaning material has a water contact angle of 105.8 + -2.1 deg in the parallel direction and a water contact angle of 123.0 + -2.6 deg in the perpendicular direction in the air, and is in a hydrophobic state; the sliding angle in the parallel direction is 15 + -1.9 deg., the sliding angle in the perpendicular direction is 79 + -2.8 deg., and the anisotropy is excellent. The liquid drop with small surface tension also has sliding anisotropy, so that different liquid drops can be selected to carry out anisotropic self-cleaning on different pollutants.

When the width of the groove is 13-17 mu m, the contact angle of the obtained self-cleaning material with air in the underwater direction is 78.3 +/-2.5 degrees along the parallel direction, and the contact angle with air in the vertical direction is 89.7 +/-3.2 degrees; the sliding angle of the test air is 17 +/-3.2 degrees in the parallel direction (taking 5 mu l of air bubbles as an example), and the sliding angle of the test air is 30 +/-2.9 degrees in the vertical direction, so that the test air has better underwater stability.

The invention further provides that the polydimethylsiloxane is prepared by adopting the following method: mixing isopropanol, dimethyl dimethoxysilane and 98% sulfuric acid aqueous solution according to the mass ratio of 100:10:1, and standing for 2-60 h;

preferably, isopropanol, dimethyldimethoxysilane and 98% sulfuric acid aqueous solution are mixed in a mass ratio of 100:10:1 and then left for 48 hours.

The second purpose of the invention is to provide a preparation method of the self-cleaning material, which comprises the following steps:

1) directionally polishing a silicon wafer material by using an abrasive material to obtain a silicon wafer with a directional groove;

2) mixing isopropanol, dimethyl dimethoxysilane and 98% sulfuric acid aqueous solution according to the mass ratio of 100:10:1, and standing for 2-60 h to obtain polydimethylsiloxane solution;

3) immersing the polished silicon wafer in the step 1) into the polydimethylsiloxane solution prepared in the step 2) for 5-10 s, and drying to obtain the silicon wafer.

Preferably, the time of grafting is 7 s.

Preferably, the abrasive is emery sandpaper.

The invention further provides that the polishing is carried out under the constant load condition that the pressure is 100-700 g by using the abrasive material with the particle size of 0.1-35 mu m.

Preferably, the grain diameter of the abrasive is 15-35 μm, the constant load pressure is 250-350 g, more preferably, the grain diameter of the abrasive is 15 μm, and the constant load pressure is 300 g.

The invention adopts the carborundum abrasive paper to carry out constant-load directional polishing on the silicon wafer, thereby providing a simpler and more convenient method for preparing the self-cleaning material with larger anisotropic adjustment range; the defects of the traditional method for manufacturing the anisotropic interface, such as laser, photoetching, electroplating and the like, which need to be assisted by specific equipment, are overcome; or the range over which the anisotropy can be adjusted is small.

The invention further provides that the preparation method further comprises drying, and/or cleaning;

preferably, the drying is specifically: drying for 3-8 min under the conditions that the humidity is 60% -70% and the temperature is 20-25 ℃.

The polydisiloxane molecular brush has strict requirements on humidity and temperature, and the sliding effect is not good due to improper temperature and humidity. Therefore, the most preferable conditions are a humidity of 65% and a temperature of 21 ℃ and drying is performed for 5min to obtain the best sliding effect.

The cleaning specifically comprises the following steps: and respectively washing with water, isopropanol and toluene.

The invention provides a preferable scheme, and the preparation method of the self-cleaning material comprises the following steps:

1) grinding the silicon wafer material in an oriented mode by adopting an abrasive material with the grain diameter of 15 microns under the condition that the constant load pressure is 300g to obtain a silicon wafer with an oriented groove;

3) immersing the polished silicon wafer in the step 1) into the polydimethylsiloxane solution prepared in the step 2) for 7s, drying and cleaning to obtain the silicon wafer;

the third purpose of the invention is to provide the self-cleaning material, which has excellent anisotropic sliding property on various liquid drops such as glycerol, formamide, formic acid, toluene and the like, water and air bubbles, can realize anisotropic self-cleaning in air and has strong underwater stability.

In particular, in the fields of surface self-cleaning, directional transport of liquid droplets, and the like.

The self-cleaning material disclosed by the invention has a good anisotropic sliding effect on oil drops with various surface tension values; different liquid drops can be selected according to different pollutants to carry out anisotropic self-cleaning on the interface. When the pollutant is sand, cleaning with water, glycerol, formamide, dimethyl sulfoxide (DMSO), etc.; when the pollutant is rhodamine B, glycerol, formamide, DMSO and the like can be used for cleaning; when the pollutant is graphite, DMSO and formic acid can be used for cleaning;

drawings

FIG. 1 is an SEM scanning electron microscope image of a polished silicon wafer obtained in step 1) of example 2;

FIG. 2 is a graph showing the change of contact angle and sliding angle of the self-cleaning material prepared in examples 2-7 in the parallel and vertical directions with respect to a water droplet;

FIG. 3 shows the surface tension of the self-cleaning material of embodiment 2 ranging from 72.8 mNm to 28.4mNm^-1A sliding signature comparison plot for varying range drops;

FIG. 4 is a graph showing the sliding angle changes of the self-cleaning material of example 2 in the parallel and vertical directions for different volumes of air under water.

FIG. 5 is a comparative graph of anisotropic self-cleaning in both the vertical and parallel directions for the self-cleaning material of example 2;

Detailed Description

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

The dimensions of the wafers used in the following examples were 2cm by 2 cm.

Example 1

The embodiment provides a self-cleaning material grafted by a molecular brush, which takes a silicon wafer as a base material, wherein at least one surface of the base material is grafted with a polydimethylsiloxane molecular brush with the thickness of 4.3 +/-0.1 nm;

grooves with the width of 13-17 microns and the height of 42nm are uniformly distributed on the surface of the silicon wafer, the interval between every two adjacent grooves is 15 microns, and the polydimethylsiloxane molecular brush is grafted on the surface of the silicon wafer.

Example 2

The embodiment provides a preparation method of the self-cleaning material in embodiment 1, which comprises the following steps:

1) directionally polishing the silicon wafer by using carborundum abrasive paper with the grain diameter of 15 mu m under the constant load condition of 300g to obtain the silicon wafer with directional grooves; (as shown in FIG. 1)

2) Mixing isopropanol, dimethyl dimethoxysilane and 98% sulfuric acid aqueous solution according to the mass ratio of 100:10:1, and standing for 48h to obtain polydimethylsiloxane solution;

3) immersing the polished silicon wafer in the step 1) into the polydimethylsiloxane solution prepared in the step 2) for 7s, drying, and washing with water, isopropanol and toluene respectively to obtain the silicon wafer.

Examples 3 to 7

This example provides a method for preparing a molecular brush grafted self-cleaning material, differing from example 2 only in that the grain size of the emery paper was replaced by 0.1 μm, 1 μm, 3 μm, 9 μm and 30 μm.

Comparative example 1

This comparative example provides a self-cleaning material, which differs from example 1 only in that the thickness of the polydimethylsiloxane molecular brush was changed from 4.3. + -. 0.1nm to 2-2.5 nm.

Comparative example 2

This comparative example provides a self-cleaning material, which is different from example 1 only in that the thickness of the polydimethylsiloxane molecular brush was changed to 4.3. + -. 0.1nm to 6.5 to 7.5 nm.

Test example 1

1. In the air, a contact angle measuring instrument is adopted to test the contact angle and the sliding angle of the water drops of the self-cleaning material prepared in the embodiment 2-7 and the self-cleaning material described in the comparative example 1-2 in the parallel direction and the vertical direction; the sliding angle of the drops was tested for 5 μ l drops as an example and the results are as follows:

TABLE 1

As shown in FIG. 2, the sliding angle of the self-cleaning interface in the horizontal direction is substantially constant and the sliding angle in the vertical direction is significantly increased as the particle size of the abrasive is increased. The maximum slip anisotropy was achieved when the abrasive grain size was 15 μm (self-cleaning material made in example 2): the slide angle along the parallel direction is 15.0 ° ± 1.9 °, and the slide angle along the perpendicular direction is 79.0 ° ± 2.8 °. In comparative examples 1 and 3, too short or too long graft chain results in large sliding angle in both directions and poor sliding property.

2. The self-cleaning material described in example 2 was tested for sliding angle in the parallel and perpendicular directions for droplets of various surface tensions, with the following results:

TABLE 2

As shown in fig. 3, the sliding angle in both the parallel and perpendicular directions decreased as the surface tension of various droplets decreased, and the difference in the sliding angle between the two directions also decreased.

3. The sliding angles of different volumes of bubbles of the self-cleaning material described in example 1 in the parallel and perpendicular directions were tested in water with the following results:

TABLE 3

Bubble volume (μ l)	Sliding angle value in parallel direction (°)	Sliding angle value in vertical direction (°)
			4	25.2±2.9	45.0±3.7
7	20.4±3.1	38.3±3.3
			10	17.8±3.2	30.1±2.9
15	14.2±2.5	23.7±3.1
			20	11.3±2.3	16.7±2.6
30	8.5±2.8	9.1±2.0

As shown in FIG. 4, for 10. mu.l of the bubble, the slide angles measured in the parallel and perpendicular directions were 17.8. + -. 3.2 ℃ and 30.1. + -. 2.9 ℃ respectively, and the difference in the slide angles in the two directions became smaller as the volume of the bubble increased.

Test example 2

The self-cleaning material described in example 1 was subjected to a cleaning test;

smearing hydrophilic sandy soil on one position of the surface of the self-cleaning material, dripping water drops beside the hydrophilic sandy soil, and inclining the self-cleaning material by a certain angle (15 degrees) to enable the water drops to pass through the hydrophilic sandy soil; multiple experiments were performed in parallel. As shown in fig. 5, the upper part is the non-inclined self-cleaning material, and the lower part is the inclined part; as can be seen, the water drops self-clean the hydrophilic sandy soil anisotropically in both the vertical and parallel directions.

Although the invention has been described in detail hereinabove by way of general description, specific embodiments and experiments, it will be apparent to those skilled in the art that many modifications and improvements can be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims

1. A self-cleaning material grafted by molecular brushes is characterized in that a silicon wafer material is used as a base material, and polydimethylsiloxane molecular brushes with the thickness of 4.0-4.5 nm are grafted on at least one surface of the base material;

grooves with the width of 0.1-35 mu m and the height of 5-60 nm are uniformly distributed on the surface of the base material, and the polydimethylsiloxane molecular brush is grafted on the surface of the base material;

the preparation method of the self-cleaning material comprises the following steps:

1) the method comprises the following steps of directionally polishing a silicon wafer material by using an abrasive to obtain a silicon wafer with a directional groove, wherein the polishing is specifically performed by using the abrasive with the particle size of 15-35 mu m under the constant load condition of the pressure of 250-350 g;

3) immersing the polished silicon wafer in the step 1) into the polydimethylsiloxane solution prepared in the step 2) for 5-10 s, and drying for 3-8 min under the conditions that the humidity is 60% -70% and the temperature is 20-25 ℃ to obtain the silicon wafer.

2. The self-cleaning material of claim 1, wherein the silicon wafer material has a length and width of 1-5 cm and 1-5 cm.

3. The self-cleaning material of claim 2, wherein the silicon wafer material is 2cm by 2cm long.

4. The self-cleaning material as claimed in any one of claims 1 to 3, wherein the width of the grooves is 12 to 35 μm and the height is 29 to 60 nm.

5. The self-cleaning material of claim 4, wherein the trenches have a width of 13-17 μm and a height of 40-50 nm.

6. The self-cleaning material as claimed in any one of claims 1 to 3, wherein the spacing between adjacent grooves is 0.1 to 35 μm.

7. The self-cleaning material of claim 4, wherein the spacing between adjacent grooves is 0.1-35 μm.

8. The self-cleaning material of claim 6, wherein the spacing between adjacent grooves is 15-35 μm.

9. The self-cleaning material of claim 8, wherein the spacing between adjacent grooves is 15 μm.

10. The self-cleaning material of claim 1, wherein said polydimethylsiloxane is prepared by: isopropanol, dimethyl dimethoxysilane and 98% sulfuric acid aqueous solution are mixed according to the mass ratio of 100:10:1 and then are placed for 48 hours.

11. A method for preparing a self-cleaning material as claimed in any one of claims 1 to 10, comprising the steps of:

12. The method of claim 11, wherein the immersion time is 7 seconds.

13. The method according to claim 11, wherein the polishing is carried out under a constant load of 300g with an abrasive having a particle size of 15 μm.

14. The method of claim 13, wherein the abrasive material is emery paper.

15. The method of claim 11 or 13, further comprising, after the drying, cleaning; the cleaning specifically comprises the following steps: and respectively washing with water, isopropanol and toluene.

16. The method for preparing according to claim 11 or 14, characterized by comprising the steps of:

3) immersing the polished silicon wafer in the step 1) into the polydimethylsiloxane solution prepared in the step 2) for 7s, drying and cleaning to obtain the silicon wafer.

17. Use of the self-cleaning material of any one of claims 1 to 10 for self-cleaning in air, water, glycerol, formamide, formic acid, toluene.

18. The self-cleaning material prepared by the preparation method of any one of claims 11 to 16 is applied to self cleaning in air, water, glycerol, formamide, formic acid and toluene.