CN117225197A - Method for preparing PDMS film by coaxial electrostatic spray deposition - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 26
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- UKLDJPRMSDWDSL-UHFFFAOYSA-L [dibutyl(dodecanoyloxy)stannyl] dodecanoate Chemical compound CCCCCCCCCCCC(=O)O[Sn](CCCC)(CCCC)OC(=O)CCCCCCCCCCC UKLDJPRMSDWDSL-UHFFFAOYSA-L 0.000 claims description 5
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- NGNBDVOYPDDBFK-UHFFFAOYSA-N 2-[2,4-di(pentan-2-yl)phenoxy]acetyl chloride Chemical compound CCCC(C)C1=CC=C(OCC(Cl)=O)C(C(C)CCC)=C1 NGNBDVOYPDDBFK-UHFFFAOYSA-N 0.000 description 2
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Abstract
The invention discloses a method for preparing a PDMS film by adopting coaxial electrostatic spray deposition. And filling the PDMS polymer solution and the cross-linking agent solution on two sides of the spray head respectively. The two solutions are mixed at the nozzle, and under the synergistic effect of an electric field, a temperature field and a flow field, micro-nano-scale fog drops are formed, and finally, the fog drops are directionally deposited on the surface of the substrate, so that a stable ultrathin film is formed. By changing the parameters of the spray solution and the parameters of the spray process, the precise regulation and control of the membrane micro-nano structure can be realized. The PDMS membrane prepared by the invention has the advantages of high flux and good stability.
Description
Technical Field
The invention relates to a method for preparing a PDMS film by electrostatic spraying, in particular to a method for preparing a PDMS film by coaxial electrostatic spraying deposition.
Background
Polydimethylsiloxane (PDMS) is a common membrane separation material. The membrane formed by crosslinking the PDMS polymer chain can be used for recycling organic matters in water, treating VOCs in gas and coupling alcohol fermentation and membrane separation. The current commercial PDMS membranes are prepared by a coating method, and the thickness of the PDMS membranes is generally more than 10 mu m, so that the permeation flux of the membranes is low. Taking 5 wt% ethanol aqueous solution as an example, the membrane flux is generally lower than 1000 g m at 40 DEG C -2 h -1 . The low flux of the PDMS membrane can lead to the defects of large filling area, high equipment investment and the like of the membrane, and the industrial large-scale separation requirement is difficult to meet.
Electrostatic spray deposition is a more advantageous method of film formation than coating. The electrostatic spraying can accurately regulate and control key parameters such as the structure, the morphology and the like of the membrane on the micro/nano scale. In a steady spray regime, the monodisperse droplets produced by the taylor cone spray pattern range in size from a few nanometers to hundreds of microns. Under the synergistic effect of the flow field-temperature field-and the electric field, the micro-nano liquid drops directionally move towards the substrate and stably deposit on the surface of the substrate, and finally, the micro-nano ultra-thin film is formed. For example, mcfitcheon et al produced a single layer of about 15 nm ultrathin polyamide membrane with a surface roughness of less than 2nm using electrostatic spraying, significantly improved water permeability and desalination efficiency with the desired selectivity ensured. In addition, the polymer film is prepared by adopting electrostatic spraying, and the large-scale preparation of the film can be realized by simply amplifying the substrate. Chinese patent (CN 202110095371.2) describes an electrospray solution formed by dissolving polyamine/polyol monomers and polybasic acid chloride monomers/polybasic acid chloride and nanomaterial additive mixtures in a single/mixed organic solvent, respectively, and then atomizing and depositing the solution into films, respectively. Furthermore, chinese patent (CN 201880062762.0) describes a slurry that can be used for electrostatic spray deposition, comprising a solvent, a first polymer dissolved in the solvent, and polymer particles comprising a second polymer and dispersed in the solvent. The slurry is allowed to deposit stably on the substrate by electrostatic spraying and forms a film with a granular and microporous structure.
In the process of preparing PDMS films, it is difficult to work with the electrostatic spray described above. Mainly characterized in that if PDMS polymer and cross-linking agent are premixed and stirred, and then are injected into an electrostatic spray nozzle, the size of sprayed fog drops is large, the dispersibility is poor, the fine regulation and control capability on a deposited active layer is greatly weakened, even the nozzle is blocked, and the spraying process is not sustainable. If electrostatic spraying is used to alternately deposit PDMS polymer and crosslinking agent on a substrate, a delay of crosslinking reaction is caused, and too short a reaction time may result in insufficient crosslinking and poor film forming performance.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a method for preparing the PDMS film by coaxial electrostatic spray deposition, which realizes the accurate control of the thickness and the surface morphology of the PDMS film, effectively reduces the thickness of the PDMS film and improves the permeation flux of the PDMS film.
The main technical scheme adopted by the invention is as follows: a method for preparing a PDMS film by coaxial electrostatic spray deposition, which is characterized by comprising the following main steps.
(1) Electrospray solution preparation of PDMS polymers.
According to the mass parts, 1 part of PDMS monomer and 9 parts of solvent are placed in a container, and after 50 min of stirring in a magnetic stirrer, a proper amount of polar soluble substances are added, and uniformly stirred for 5 min, so as to obtain an electrospray solution of the PDMS monomer.
(2) Electrospray solution preparation of the crosslinking agent.
Taking 1 part of PDMS in the step (1) as a standard, taking 0.1-1 part of a cross-linking agent, taking 0.01 part of a catalyst and 9-9.9 parts of a solvent according to parts by mass, placing the mixture in a new container, and uniformly stirring for 5 min to obtain an electrospray solution of the cross-linking agent.
(3) And preparing the macromolecule separation membrane by coaxial electrostatic spray deposition.
And (3) respectively connecting the two electrospray solutions obtained in the step (1) and the step (2) to two sides of the coaxial spray head. The two solutions are delivered by a syringe pump at a flow rate of 0.6-1.5 ml h -1 The distance between the spray head and the substrate film was set to 3-8 cm, and a constant high-voltage electric field of 5-9 kV was applied. The spray head circularly scans above the base film, and the moving speed is 0.2-6 mm s -1 . And (5) circulating for a certain number of times to obtain the formed PDMS film. And (3) placing the film in an oven at 60-120 ℃ and drying 8 h to obtain a PDMS film finished product.
In step (1), the PDMS polymer may be hydroxyl-terminated or vinyl-terminated. The hydroxyl-terminated PDMS polymer uses dibutyl tin dilaurate as a catalyst, and the vinyl-terminated PDMS polymer uses platinum as a catalyst.
In the step (1) and the step (2), the solvents of the two solutions may be the same or different. The solvent is based on a nonpolar organic solvent including, but not limited to, n-heptane, isooctane, toluene, pentane, chloroform, and the like.
The polar substance added in the step (1) may be added to the vessel of the step (2) alone. Importantly, the solution incorporating the polar material requires a shell attached to the coaxial spray head.
The relative proportions of the two solutions in step (1) and step (2) can also be suitably adjusted depending on the choice of the particular solvent and catalyst, as well as the experimental requirements.
For step (3), in the coaxial spray device, the PDMS polymer solution may be either a shell or a core, and it is recommended that the PDMS polymer solution be a shell.
The base film in step (3) should have a porous structure. Pore structures of the base film include, but are not limited to, finger pores, mesh pores, and the like. Materials from which the base film is constructed include, but are not limited to, polymeric films, metallic films, ceramic films, and the like. The pore size of the base film is in the range of 5 nm-10 μm. And plugging the pore canal of the base film by adopting a template agent before spraying, and removing the template solvent after spraying.
In the technical scheme of the invention, the membrane structure can be regulated and controlled by changing the operating conditions such as spray voltage, spray height, spray speed, spray cycle number and the like. The regulation and control of the membrane structure can also be realized by changing the concentration of the PDMS polymer solution, the concentration of the cross-linking agent solution and the proportion between the polymer and the cross-linking agent.
Compared to prior art solutions, the present study has the following advantages.
(1) The invention has the advantages of easy obtaining of the equipment operated, simple preparation process of the membrane, application to large-area spray deposition and hopeful realization of large-scale industrial separation application.
(2) The technology can adopt a coaxial electrostatic spray deposition method, enhances the diffusion mass transfer of solutes, optimizes the crosslinking reaction of monomers, improves the crosslinking rate of the monomers, and obviously improves the crosslinking density of the separation membrane. The stability of the membrane separation and the service life will be significantly improved.
(3) The micron-sized charged liquid drops generated by electrostatic spraying are utilized to realize the precise control of the surface appearance, and the hydrophilic and hydrophobic properties and selective adsorptivity of the membrane can be regulated.
(4) The preparation method realizes micron-scale fine regulation. The good dispersion performance of the liquid drops ensures the uniform distribution of the film liquid and ensures the uniform thickness of the selective layer. By changing the cycle spraying times, the controllable growth of the separation membrane can be realized, and the advantage of precisely controlling the membrane thickness is played. The method can greatly reduce the thickness of the membrane and remarkably improve the permeation flux of the membrane.
(5) The PDMS membrane prepared by the method can be used in the field of molecular separation, including but not limited to alcohol-water separation, removal of VOCs in water, gas separation, fermentation and membrane separation coupling and other processes.
Drawings
Fig. 1 is a schematic diagram of an in-line electrostatic spray deposition process.
Fig. 2 is a cross-sectional scanning electron microscope image showing the use of a PDMS composite film according to an embodiment of the present invention.
Fig. 3 is an atomic force microscope image showing a surface of a PDMS composite film using an embodiment according to the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples, but the present invention is not limited to the examples described below, and variations within the technical scope of the present invention are intended to be included in the scope of the present invention.
The formulations in examples 1-4 are shown below.
PDMS monomer 1 part = α, ω -dihydroxy polydimethylsiloxane 1.2 g; solvent 9 parts = n-heptane 10.8 g; proper amount of polar substance=ethanol 2-4 g, cross-linking agent 0.1-1 part=tetraethyl orthosilicate 0.12-1.2 g; catalyst 0.01 part = dibutyltin dilaurate 0.012 g.
Example 1.
The embodiment provides a method for preparing a high molecular separation membrane by coaxial electrostatic spray deposition, which comprises the following steps.
(1) Taking a porous Polyamide (PA) basal membrane with the aperture of 0.45 mu m, cleaning surface impurities by clean water, putting the basal membrane into a drying oven for drying at the temperature of 60 ℃ for 1 h, and taking out for later use. Adding enough deionized water into a culture dish, spreading the PA base film on the surface of the deionized water, standing for thirty minutes, and allowing the water to fully permeate into the film holes to occupy the positions so as to prevent the active layer film liquid from penetrating during spray deposition.
(2) Alpha, omega-dihydroxy Polydimethylsiloxane (PDMS) 1.2 g and solvent n-heptane 10.8 g are added into a beaker A, after 50 min of stirring in a magnetic stirrer, absolute ethyl alcohol 4 g is added, and uniform stirring is carried out for 5 min, thus obtaining an electrospray solution of PDMS monomer. To beaker B was added tetraethyl orthosilicate (TEOS) 1.2 g, n-heptane 10.8 g, dibutyltin Dilaurate (DBTL) 0.012 g, and stirred uniformly for 5 min to give an electrospray solution of the crosslinker.
(3) The solution in the beaker A is connected with the shell layer of the coaxial needle tube through the injection pump, the solution in the beaker B is connected with the core layer of the coaxial needle tube through the injection pump, and the PDMS separation active layer is prepared by adopting a coaxial electrostatic spray deposition method. The two solutions were pumped with a syringe pump at a flow rate of 1.2ml h -1 The distance between the nozzle and the base film was set to 6cm, and a constant high-voltage electric field of 7kV was applied. The spray head circularly scans above the base film, and the moving speed is 0.75 mm s -1 . And (5) circulating for 5 times to obtain the PDMS film after deposition. Drying the composite membrane at 60 ℃ to obtain a finished product of the polymer separation membrane by 8 h.
Scanning electron microscope analysis (see fig. 2) of the cross section of the PDMS separation membrane prepared in the embodiment 1 shows that the separation active layer and the base membrane are clear in limit and the thickness is as thin as 2.3 mu m, so that the technical scheme provided by the invention can accurately control the thickness of the membrane; atomic force microscopy of the film surface (see fig. 3) showed a rough surface, ra=51.4 nm, rq=95.8 nm, indicating that the method can adjust the film surface morphology.
The coaxial electrostatically spray deposited PDMS separation membrane prepared in example 1 was subjected to Pervaporation (PV) test analysis. At 40 ℃, 120L h -1 PV experiments were performed on 5 wt% ethanol/water solution with membrane permeation flux up to 2522 g m -2 h -1 The separation factor is 7.65, and the PDMS separation membrane prepared by most other technical means with higher flux is greatly improved, thus showing ideal separation performance。
Example 2.
The embodiment provides a method for preparing a high molecular separation membrane by coaxial electrostatic spray deposition, which comprises the following steps.
(1) (2) refer to examples 1 (1) and (2).
(3) The solution in the beaker A is connected with the shell layer of the coaxial needle tube through the injection pump, the solution in the beaker B is connected with the core layer of the coaxial needle tube through the injection pump, and the PDMS separation active layer is prepared by adopting a coaxial electrostatic spray deposition method. The two solutions were pumped with a syringe pump at a flow rate of 1.2ml h -1 The distance between the nozzle and the base film was set at 6cm, and a constant high-voltage electric field of 7kV was applied. The spray head circularly scans above the base film, and the moving speed is 0.75 mm s -1 . And cycling for 10 times to obtain the PDMS film after deposition. Drying the composite membrane at 60 ℃ to obtain a finished product of the polymer separation membrane by 8 h.
The coaxial electrostatically spray deposited PDMS separation membrane prepared in example 2 was subjected to Pervaporation (PV) test analysis. At 40 ℃, 120L h -1 PV experiments were performed on 5 wt% ethanol/water solution with a membrane permeation flux of 1420.4 g m -2 h -1 The separation factor was 8.14.
Example 3.
(1) (2) refer to examples 1 (1) and (2).
(3) The solution in the beaker A is connected with the shell layer of the coaxial needle tube through the injection pump, the solution in the beaker B is connected with the core layer of the coaxial needle tube through the injection pump, and the PDMS separation active layer is prepared by adopting a coaxial electrostatic spray deposition method. The two solutions were pumped with a syringe pump at a flow rate of 1.2ml h -1 The distance between the nozzle and the base film was set to 6cm, and a constant high-voltage electric field of 7kV was applied. The spray head circularly scans above the base film, and the moving speed is 0.75 mm s -1 . And cycling for 20 times to obtain the PDMS film after the deposition. Drying the composite membrane at 60 ℃ to obtain a finished product of the polymer separation membrane by 8 h.
The coaxial electrostatically spray deposited PDMS separation membrane prepared in example 3 was subjected to Pervaporation (PV) test analysis. At 40 ℃, 120L h -1 Under the condition of 5 wt%PV experiments were performed with ethanol/water solutions of (A) and the permeation flux of the membrane reached 855 g m -2 h -1 The separation factor was 8.46.
Example 4.
(1) (2) refer to examples 1 (1) and (2).
(3) The solution in the beaker A is connected with the shell layer of the coaxial needle tube through the injection pump, the solution in the beaker B is connected with the core layer of the coaxial needle tube through the injection pump, and the PDMS separation active layer is prepared by adopting a coaxial electrostatic spray deposition method. The two solutions were pumped with a syringe pump at a flow rate of 1.5 ml h -1 The distance between the nozzle and the base film was set at 9 cm, and a constant high-voltage electric field of 8 kV was applied. The spray head circularly scans above the base film, and the moving speed is 0.75 mm s -1 . And (6) circulating for 6 times to obtain the PDMS film after deposition. Drying the composite membrane at 60 ℃ to obtain a finished product of the polymer separation membrane by 8 h.
The coaxial electrostatically spray deposited PDMS separation membrane prepared in example 4 was subjected to Pervaporation (PV) test analysis. At 40 ℃, 120L h -1 PV experiments were performed on 5 wt% ethanol/water solution with membrane permeation flux up to 1944 g m -2 h -1 The separation factor was 8.20.
The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (11)
1. A method for preparing a PDMS film by coaxial electrostatic spray deposition is characterized in that a PDMS polymer solution and a cross-linking agent solution are formed into micron-sized mist drops by coaxial electrostatic spray, and are cross-linked in a limited space, and finally are deposited to form the PDMS film.
2. According to claim 1, in the electrostatic spraying process, the PDMS polymer solution and the crosslinker solution move on the shell side and the core side respectively and are mixed at the nozzle, and the mixed liquid forms micron mist droplets under the action of an electrostatic field, and the solvent volatilizes and the crosslinking reaction is realized in the descending process, so that a dense PDMS film is finally deposited on the base film.
3. According to claim 2, the PDMS polymers can be hydroxyl-terminated or vinyl-terminated.
4. According to claim 2, the base membrane has a porous structure, the pore structure of which includes but is not limited to finger pores, mesh pores, etc., and the pore diameter of the base membrane is in the range of 5 nm-10 μm.
5. According to claim 4, the material for constructing the base film comprises, but is not limited to, a polymer film, a metal film, a ceramic film and the like, the pore canal of the base film is plugged by using a template agent before spraying, and the template solvent is removed after spraying is completed.
6. According to claim 1, the PDMS polymer and the cross-linking agent are respectively dissolved in corresponding solvents to respectively form a PDMS polymer solution and a cross-linking agent solution, and the solvents of the two solutions can be the same or different, and the solvents are mainly nonpolar organic solvents, including but not limited to n-heptane, isooctane, toluene, pentane, chloroform and the like.
7. According to claim 1, a certain amount of polar substances are added into the solvent to increase the conductivity of the solution and improve the stability of electrostatic spraying, wherein the polar substances include but are not limited to methanol, ethanol, acetone and the like.
8. The hydroxyl terminated PDMS polymer according to claim 3, using dibutyl tin dilaurate as catalyst and vinyl terminated PDMS polymer using platinum as catalyst.
9. According to claim 6, the catalyst can be added to the PDMS polymer solution or to the crosslinker solution either alone or in combination.
10. According to claim 2, the membrane structure can be regulated by changing the operating conditions such as spraying voltage, spraying height, spraying speed, spraying cycle number and the like, and also can be regulated by changing the concentration of the PDMS polymer solution, the concentration of the cross-linking agent solution and the proportion between the polymer and the cross-linking agent.
11. According to claim 1, the PDMS membrane is used in the field of molecular separation, including but not limited to alcohol-water separation, removal of VOCs in water, gas separation and coupling of fermentation and membrane separation.
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