CN106582332A - Method for preparing superhydrophobic composite microporous membrane - Google Patents

Abstract

The invention relates to a preparation method of a superhydrophobic composite microporous membrane. The method includes the following steps: first, a highly hydrophobic microporous membrane of polyvinylidene fluoride (PVDF) is prepared by a rough substrate-assisted phase inversion method as a base membrane, and then a uniform dispersion of multi-walled carbon nanotubes (MWCNTs) is prepared, and a constant pressure filtration method is used , use the prepared PVDF base membrane to filter the MWCNTs dispersion under constant pressure to obtain a PVDF/MWCNTs composite membrane, and then coat it with a n-hexane solution of polydimethylsiloxane (PDMS) to obtain PVDF/MWCNTs/ PDMS superhydrophobic composite microporous membrane. The static water contact angle of the composite microporous membrane obtained by the present invention can reach 162°, the rolling angle is 10°-20°, the nitrogen flux at 100kPa is >0.3m ³ /(m ² ·s), and the tensile strength is >2.6 MPa, elongation at break>96%, can be applied to membrane contact processes such as membrane distillation and membrane absorption.

Description

A kind of preparation method of superhydrophobic composite microporous membrane

technical field

The invention relates to a method for preparing a super-hydrophobic composite microporous membrane, specifically a method for preparing a PVDF/MWCNTs composite membrane by filtering a uniform dispersion of multi-walled carbon nanotubes with a PVDF base membrane under constant pressure conditions, and then passing polydimethylformaldehyde A method for preparing PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane by coating with n-hexane solution of base siloxane (PDMS).

Background technique

In recent years, superhydrophobic surfaces (surfaces with a contact angle with water greater than 150°) have received much attention. Studies have shown that the construction of superhydrophobic surfaces can start from two aspects: increasing surface roughness and reducing surface energy. Polyvinylidene fluoride (PVDF) is widely used in the preparation of separation membranes due to its excellent physical and chemical properties. However, PVDF hydrophobic membranes still have problems such as membrane hydrophilic penetration and pollution resistance. Therefore, PVDF membranes are superhydrophobic. Modification to improve its hydrophobicity and antifouling properties has become a key issue to be solved urgently. With the development of functional materials, the combination of inorganic nanomaterials and polymers to prepare composite materials has attracted widespread attention. Carbon nanotubes (CNTs) have become one of the most popular nanomaterials due to their structural specificity and unique physical and chemical properties. At present, there have been many reports on carbon nanotube/polymer composite films, most of which are prepared by adding carbon nanotubes to polymer solutions and blending to prepare composite films. The main function is to change the overall performance of the polymer. Preparation methods and studies focusing on their effects on surface properties are rarely reported.

Contents of the invention

The object of the present invention is to provide a method for preparing a super-hydrophobic composite microporous membrane aiming at the deficiencies in the current technology. In this method, the multi-walled carbon nanotubes are inserted into the micropores of the PVDF highly hydrophobic base membrane (the contact angle with water is about 120°) by constant pressure filtration method, and the nanoscale structure is constructed on the basis of the original micron-scale structure on the surface of the membrane. The formation of a micro-nano composite hierarchical structure increases the surface roughness of the film, and then the free energy of the film surface is reduced by coating PDMS solution. The two aspects synergistically increase the contact angle of the film surface and reduce the rolling angle of the film surface. PVDF /MWCNTs/PDMS superhydrophobic composite microporous membrane.

A preparation method of a superhydrophobic composite microporous membrane, comprising the following steps:

(1) Preparation of PVDF highly hydrophobic microporous membrane by rough substrate-assisted phase inversion method: after dissolving the casting solution and standing for defoaming, place it on the substrate, and scrape a liquid film with a thickness of 0.15 μm-0.2 μm on the substrate , the liquid film is induced by water vapor, phase-separated in a coagulation bath, solidified into a solid film, removed from the substrate, soaked in deionized water and ethanol in turn, and dried at room temperature to obtain a PVDF highly hydrophobic microporous film; The substrate is an aluminum alloy plate with a micron-scale rough structure on the surface; the mass percentage of the casting solution is composed of polyvinylidene fluoride (PVDF) 10%-14%, n-octanol 6%-10%, and the rest is a solvent ;

(2) Dissolve multi-walled carbon nanotubes (MWCNTs) and carbon nanotube dispersant in deionized water, after stirring evenly, first ultrasonically treat for 30min-60min, and then centrifuge for 30min-60min to obtain a concentration of 0.01wt%-0.05 wt% carbon nanotube dispersion; the quality of the carbon nanotube dispersant is 25%-35% of the mass of the carbon nanotubes used;

(3) Under a constant 0.05MPa-0.25MPa filtration pressure difference, use the PVDF base membrane prepared in step (1) to filter the MWCNTs uniform dispersion liquid configured in step (2) while stirring in the filter, wherein, the micron-scale The surface of the PVDF base film of the aluminum alloy plate with a rough structure faces the MWCNTs dispersion side. After the filtration is completed, MWCNTs are evenly distributed on the film surface facing the MWCNTs dispersion side to obtain a PVDF/MWCNTs composite film. dry, ready to use;

(4) Dissolve polydimethylsiloxane (PDMS) in n-hexane, and configure a n-hexane solution with a PDMS concentration of 1wt%-8wt% as a coating solution; compound the PVDF/MWCNTs prepared in step (3) The film is fixed on a smooth glass plate with the surface of the film distributed with MWCNTs facing up; then the glass plate is horizontally immersed in the coating solution with the side with the film facing up, and it is taken out horizontally after 2s-5s to obtain PVDF/MWCNTs/ PDMS superhydrophobic composite microporous membrane.

The carbon nanotube dispersant is specifically one of carbon nanotube water dispersant (TNWDIS), sodium dodecyl sulfate (SDS), and Triton X-100.

The solvent of the casting solution in the step (1) is N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) or N-methylpyrrolidone (NMP).

The carbon nanotubes are multi-walled carbon nanotubes, hydroxylated multi-walled carbon nanotubes or carboxylated multi-walled carbon nanotubes.

The aluminum alloy plate with a micron-scale rough structure on the surface is prepared by the following steps: prepare an oxalic acid solution with a concentration of 0.08 mol/L and a hydrochloric acid solution with a concentration of 1 mol/L, and blend them at a volume ratio of 1:1 to obtain a mixed acid, It is obtained after immersing the aluminum alloy plate in the mixed acid solution for 6h-10h.

The beneficial effects of the present invention are:

Different from the commonly used method of blending carbon nanotubes and polymer solutions to prepare carbon nanotube/polymer composite membranes, the present invention uses a constant pressure filtration method to press multi-walled carbon nanotubes into the micropores of PVDF base membranes to prepare composite membranes , to build a nanoscale structure on the basis of the original micron-scale structure on the film surface to form a micro-nano composite hierarchical structure. Compared with other nanoparticles, the addition of MWCNTs not only increases the surface roughness of the membrane, but also ensures the permeability of the membrane due to its own tubular structure. Coating PDMS with low surface energy on the surface of PVDF/MWCNTs composite film reduces the free energy of the film surface. The synergistic effect of MWCNTs and PDMS increases the contact angle of the film surface, reduces the rolling angle of the film surface, and improves the hydrophobicity of the film. performance. The composite microporous membrane prepared according to the present invention has superhydrophobicity, the contact angle between the membrane surface and water can reach 162°, the rolling angle is 10°-20°, and the nitrogen flux at 100kPa is >0.3m ³ /(m ² · s), tensile strength>2.6MPa, elongation at break>96%.

Description of drawings

Fig. 1 is a schematic flow sheet of the present invention;

Figure 2 is a schematic diagram of a device for preparing PVDF/MWCNTs composite membranes by constant pressure filtration;

Fig. 3 is the surface SEM figure of the PVDF base film and PVDF/MWCNTs composite film that embodiment 3 obtains; Surface SEM image;

Fig. 4 is the surface AFM figure of the PVDF base film and PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane that embodiment 3 obtains, and wherein, Fig. 4 (a) is the surface AFM figure of PVDF base film, Fig. 4 (b) is Surface AFM image of PVDF/MWCNTs/PDMS composite film;

Fig. 5 is respectively the water contact angle test figure of the PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane surface that embodiment 2,3,4 obtains;

specific embodiment

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Example 1

The configuration quality composition is respectively polyvinylidene fluoride (PVDF)-10%, N,N-dimethylacetamide (DMAc)-84%, n-octanol (1-Octanol)-6% casting solution is placed in 70 In a vacuum drying oven at ℃, the casting solution is completely dissolved and mixed evenly, then the temperature is adjusted to 35 ℃ and left to defoam for 2 days, and the casting solution is evenly scraped on the aluminum alloy plate chemically etched for 8 hours with a scraper. Form a liquid film with a thickness of 0.15 μm-0.2 μm on the plate, place the liquid film in a constant temperature and humidity chamber with a relative humidity of 95% to induce water vapor for 5 minutes, and then immerse the liquid film in a pure water coagulation bath at 35°C for phase separation After 0.5h, the liquid film is solidified into a solid film, removed from the aluminum alloy plate, soaked in deionized water for 2 days, then immersed in ethanol for 1 day, taken out the solid film and dried at room temperature to obtain a PVDF highly hydrophobic microporous film .

In the step (1), the substrate is an aluminum alloy plate (the model is S6061, mainly containing Mg and Si elements, and it is a cold-processed aluminum forged product) in the concentration of 0.08mol/L oxalic acid solution and 1mol/L hydrochloric acid The aluminum alloy plate obtained after soaking in the mixed acid solution prepared by blending the solution at a volume ratio of 1:1 for 8 hours has a micron-scale rough structure on the surface.

Weigh 0.01g of carboxylated multi-walled carbon nanotubes (MWCNTs) and 0.003g of carbon nanotube water dispersant (TNWDIS) and dissolve them in 99.987g of deionized water. Then centrifuge for 40min (5000r/min) to obtain a uniform dispersion of carbon nanotubes. Under the filtration pressure difference of 0.15MPa, the above-mentioned PVDF highly hydrophobic microporous membrane is used as the base membrane, and the base membrane is installed in the filter, and the surface of the membrane that replicates the micron-scale rough structure on the aluminum alloy plate faces the MWCNTs dispersion side, while stirring (400r/min) while filtering the uniform dispersion, after the filtration is completed, a PVDF/MWCNTs composite membrane is obtained, MWCNTs are evenly distributed on the membrane surface facing the MWCNTs dispersion side, and there is no MWCNTs distribution on the other side, and the obtained PVDF/MWCNTs composite The membrane was allowed to dry at room temperature for use.

Dissolve 7.8ml of PDMS in 252.2ml of n-hexane to prepare the coating solution. Use adhesive tape to fix the neatly cut PVDF/MWCNTs composite film on a smooth glass plate. The surface of the film with MWCNTs distributed is facing up, and the other side is close to the glass plate. Then immerse the glass plate into the coating solution horizontally, with the film side up, take it out horizontally after 3 seconds, and dry it at room temperature to obtain the PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane.

The contact angle of PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane with water is 159° and the rolling angle is 19° measured by a dynamic/static contact angle meter; the nitrogen flux at 100kPa measured by a flux testing device is 0.31 m ³ /(m ² ·s), the tensile strength and elongation at break of PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane were 2.62MPa and 96.8%, respectively, measured by electronic single yarn strength tester.

Example 2

The configuration quality composition is respectively polyvinylidene fluoride (PVDF)-10%, N,N-dimethylacetamide (DMAc)-84%, n-octanol (1-Octanol)-6% casting solution is placed in 70 In a vacuum drying oven at ℃, the casting solution is completely dissolved and mixed evenly, then the temperature is adjusted to 35 ℃ and left to defoam for 2 days, and the casting solution is evenly scraped on the aluminum alloy plate chemically etched for 8 hours with a scraper. Form a liquid film with a thickness of 0.15 μm-0.2 μm on the plate, place the liquid film in a constant temperature and humidity chamber with a relative humidity of 95% to induce water vapor for 5 minutes, and then immerse the liquid film in a pure water coagulation bath at 35°C for phase separation After 0.5h, the liquid film was solidified into a solid film, removed from the aluminum alloy plate, soaked in deionized water for 2 days, and then soaked in ethanol for 1 day, took out the solid film and dried it at room temperature to obtain a PVDF highly hydrophobic microporous film .

Weigh 0.03g of carboxylated multi-walled carbon nanotubes (MWCNTs) and 0.009g of carbon nanotube water dispersant (TNWDIS) and dissolve them in 99.961g of deionized water. Then centrifuge for 40min (5000r/min) to obtain a uniform dispersion of carbon nanotubes. Under the filtration pressure difference of 0.2MPa, the above-mentioned PVDF highly hydrophobic microporous membrane is used as the base membrane, and the base membrane is installed in the filter, and the surface of the membrane that replicates the micron-scale rough structure on the aluminum alloy plate faces the MWCNTs dispersion side, while stirring (400r/min) while filtering the uniform dispersion, after the filtration is completed, a PVDF/MWCNTs composite membrane is obtained, MWCNTs are evenly distributed on the membrane surface facing the MWCNTs dispersion side, and there is no MWCNTs distribution on the other side, and the obtained PVDF/MWCNTs composite The membrane was allowed to dry at room temperature for use.

Dissolve 7.8ml of PDMS in 252.2ml of n-hexane to prepare the coating solution. Use adhesive tape to fix the neatly cut PVDF/MWCNTs composite film on a smooth glass plate. The surface of the film with MWCNTs distributed is facing up, and the other side is close to the glass plate. Then immerse the glass plate into the coating solution horizontally, with the film side up, take it out horizontally after 3 seconds, and dry it at room temperature to obtain the PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane.

The method of testing membrane performance is identical with embodiment 1, and the contact angle of PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane membrane surface and water is 161 °, and rolling angle is 16 °, and the nitrogen flux under 100kPa is 0.34m ³ /(m ² ·s), the tensile strength is 2.61MPa, and the elongation at break is 97.0%.

Example 3

The configuration quality composition is respectively polyvinylidene fluoride (PVDF)-10%, N,N-dimethylacetamide (DMAc)-84%, n-octanol (1-Octanol)-6% casting solution is placed in 70 In a vacuum drying oven at ℃, the casting solution is completely dissolved and mixed evenly, then the temperature is adjusted to 35 ℃ and left to defoam for 2 days, and the casting solution is evenly scraped on the aluminum alloy plate chemically etched for 8 hours with a scraper. Form a liquid film with a thickness of 0.15 μm-0.2 μm on the plate, place the liquid film in a constant temperature and humidity chamber with a relative humidity of 95% to induce water vapor for 5 minutes, and then immerse the liquid film in a pure water coagulation bath at 35°C for phase separation After 0.5h, the liquid film was solidified into a solid film, removed from the aluminum alloy plate, soaked in deionized water for 2 days, and then soaked in ethanol for 1 day, took out the solid film and dried it at room temperature to obtain a PVDF highly hydrophobic microporous film .

Weigh 0.03g of carboxylated multi-walled carbon nanotubes (MWCNTs) and 0.009g of carbon nanotube water dispersant (TNWDIS) and dissolve them in 99.961g of deionized water. Then centrifuge for 40min (5000r/min) to obtain a uniform dispersion of carbon nanotubes. Under the filtration pressure difference of 0.15MPa, the above-mentioned PVDF highly hydrophobic microporous membrane is used as the base membrane, and the base membrane is installed in the filter, and the surface of the membrane that replicates the micron-scale rough structure on the aluminum alloy plate faces the MWCNTs dispersion side, while stirring (400r/min) while filtering the uniform dispersion, after the filtration is completed, a PVDF/MWCNTs composite membrane is obtained, MWCNTs are evenly distributed on the membrane surface facing the MWCNTs dispersion side, and there is no MWCNTs distribution on the other side, and the obtained PVDF/MWCNTs composite The membrane was allowed to dry at room temperature for use.

Dissolve 7.8ml of PDMS in 252.2ml of n-hexane to prepare the coating solution. Use adhesive tape to fix the neatly cut PVDF/MWCNTs composite film on a smooth glass plate. The surface of the film with MWCNTs distributed is facing up, and the other side is close to the glass plate. Then immerse the glass plate into the coating solution horizontally, with the film side up, take it out horizontally after 3 seconds, and dry it at room temperature to obtain the PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane.

The method for testing membrane performance is the same as in Example 1, the contact angle of PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane membrane surface water is 162 °, the rolling angle is ¹² °, and the nitrogen flux under 100kPa is 0.33m /(m ² ·s), the tensile strength is 2.65MPa, and the elongation at break is 97.4%.

Example 4

The configuration quality composition is respectively polyvinylidene fluoride (PVDF)-10%, N,N-dimethylacetamide (DMAc)-84%, n-octanol (1-Octanol)-6% casting solution is placed in 70 In a vacuum drying oven at ℃, the casting solution is completely dissolved and mixed evenly, then the temperature is adjusted to 35 ℃ and left to defoam for 2 days, and the casting solution is evenly scraped on the aluminum alloy plate chemically etched for 8 hours with a scraper. Form a liquid film with a thickness of 0.15 μm-0.2 μm on the plate, place the liquid film in a constant temperature and humidity chamber with a relative humidity of 95% to induce water vapor for 5 minutes, and then immerse the liquid film in a pure water coagulation bath at 35°C for phase separation After 0.5h, the liquid film is solidified into a solid film, removed from the aluminum alloy plate, soaked in deionized water for 2 days, then immersed in ethanol for 1 day, taken out the solid film and dried at room temperature to obtain a PVDF highly hydrophobic microporous film .

Weigh 0.03g of carboxylated multi-walled carbon nanotubes (MWCNTs) and 0.009g of carbon nanotube water dispersant (TNWDIS) and dissolve them in 99.961g of deionized water. Then centrifuge for 40min (5000r/min) to obtain a uniform dispersion of carbon nanotubes. Under the filtration pressure difference of 0.15MPa, the above-mentioned PVDF highly hydrophobic microporous membrane is used as the base membrane, and the base membrane is installed in the filter, and the surface of the membrane that replicates the micron-scale rough structure on the aluminum alloy plate faces the MWCNTs dispersion side, while stirring (400r/min) while filtering the uniform dispersion, after the filtration is completed, a PVDF/MWCNTs composite membrane is obtained, MWCNTs are evenly distributed on the membrane surface facing the MWCNTs dispersion side, and there is no MWCNTs distribution on the other side, and the obtained PVDF/MWCNTs composite The membrane was allowed to dry at room temperature for use.

Dissolve 13.0ml of PDMS in 247.0ml of n-hexane to prepare the coating solution. Use adhesive tape to fix the neatly cut PVDF/MWCNTs composite film on a smooth glass plate. The surface of the film with MWCNTs distributed is facing up, and the other side is close to the glass plate. Then immerse the glass plate into the coating solution horizontally, with the film side up, take it out horizontally after 3 seconds, and dry it at room temperature to obtain the PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane.

The method of testing membrane performance is identical with embodiment 1, and the contact angle of PVDF/MWCNTs/PDMS superhydrophobic composite microporous membrane membrane surface and water is 160 °, and rolling angle is 18 °, and the nitrogen flux under 100kPa is 0.30m ³ /(m ² ·s), the tensile strength is 2.64MPa, and the elongation at break is 98.6%.

Individual embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention, and cannot be considered as limiting the implementation scope of the present invention. All equivalent changes and improvements made according to the application scope of the present invention shall still belong to the scope covered by the patent of the present invention.

Matters not covered in the present invention are known technologies.

Claims (5)

1. a preparation method of superhydrophobic composite microporous membrane, is characterized in that comprising the following steps: (1) Preparation of PVDF highly hydrophobic microporous membrane by rough substrate assisted phase inversion method: after dissolving the casting solution, standing for defoaming, and placing it on the substrate, a 0.15µm-0.2µm thick liquid film is formed on the substrate. The liquid film is induced by water vapor, phase-separated in a coagulation bath, solidified into a solid film, removed from the substrate, soaked in deionized water and ethanol in turn, and dried at room temperature to obtain a PVDF highly hydrophobic microporous film; The substrate is an aluminum alloy plate with a micron-scale rough structure on the surface; the mass percentage of the casting solution is composed of polyvinylidene fluoride (PVDF) 10%-14%, n-octanol 6%-10%, and the rest is a solvent; (2) Dissolve multi-walled carbon nanotubes (MWCNTs) and carbon nanotube dispersant in deionized water, stir evenly, first ultrasonically treat for 30min-60min, then centrifuge for 30min-60min, and obtain a concentration of 0.01wt%-0.05 wt% carbon nanotube uniform dispersion; the quality of the carbon nanotube dispersant is 25%-35% of the carbon nanotube mass used; (3) Under a constant 0.05MPa-0.25MPa membrane pressure difference, use the PVDF base membrane prepared in step (1) to filter the MWCNTs uniform dispersion liquid configured in step (2) while stirring in the filter, wherein, the contact micron The surface of the PVDF base film of the super-rough structure aluminum alloy plate faces the MWCNTs dispersion liquid side. After the filtration is completed, MWCNTs are uniformly distributed on the film surface facing the MWCNTs dispersion liquid side to obtain a PVDF/MWCNTs composite film. The obtained PVDF/MWCNTs composite film is placed at room temperature Let dry and set aside; (4) Dissolve polydimethylsiloxane (PDMS) in n-hexane, and configure a n-hexane solution with a PDMS concentration of 1wt%-8wt% as a coating solution; compound the PVDF/MWCNTs prepared in step (3) The film is fixed on a smooth glass plate with the surface of the film distributed with MWCNTs facing up; then the glass plate is horizontally immersed in the coating solution with the side with the film facing up, and it is taken out horizontally after 2s-5s to obtain PVDF/MWCNTs/ PDMS superhydrophobic composite microporous membrane. 2. The preparation method of superhydrophobic composite microporous membrane as claimed in claim 1, characterized in that said carbon nanotube dispersant is specifically carbon nanotube water dispersant (TNWDIS), sodium dodecyl sulfate (SDS ), one of Triton X-100. 3. The preparation method of the superhydrophobic composite microporous membrane as claimed in claim 1, characterized in that the solvent of the casting solution in the step (1) is N,N-dimethylacetamide (DMAc), N , N-dimethylformamide (DMF) or N-methylpyrrolidone (NMP). 4. the preparation method of superhydrophobic composite microporous membrane as claimed in claim 1 is characterized in that described carbon nanotube is multi-walled carbon nanotube, hydroxylated multi-walled carbon nanotube or carboxylated multi-walled carbon nanotube . 5. the preparation method of superhydrophobic composite microporous membrane as claimed in claim 1 is characterized in that described surface has the aluminum alloy plate of micron-scale rough structure to make by the following steps: preparation concentration is the oxalic acid of 0.08mol/L Solution and 1mol/L hydrochloric acid solution are blended at a volume ratio of 1:1 to obtain a mixed acid, which is obtained by soaking an aluminum alloy plate in the mixed acid solution for 6h-10h.