PDMS hydrophilic modification method and modified PDMS with hydrophilic coating

Abstract

The invention discloses a simple and effective PDMS hydrophilic modification method and PDMS with a hydrophilic coating, the hydrophilic modification method comprises the following steps: 1) adding a certain amount of a surfactant and a binder into an alcoholic solution, and stirring until the surfactant and the binder are completely dissolved; (2) adding TiO2 powder into the solution obtained in the step (1), and stirring until the solution is fully mixed; (3) dropwise adding a silane surface modifier into the solution, continuously stirring, and carrying out ultrasonic treatment to obtain a uniform mixed solution; and 4) constructing a hydrophilic coating on the surface of a PDMS substrate by using the uniform mixed solution prepared in the step 3), removing redundant solvent, and drying to obtain the modified PDMS. According to the present invention, the hydrophilic surface of the PDMS treated by using the hydrophilic modification method has long stabilization time, the water contact angle is less than 10 DEG C and even less than 7 DEG C through the test, the method is simple, convenient, effective and low in cost, and the expensive or toxic chemical reagent does not need to be used in the modification process.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film modification. Specifically, it relates to a simple and effective method for hydrophilic modification of PDMS and PDMS with a hydrophilic coating after modification. Background Art

[0002] The lithography and etching techniques for fabricating glass microfluidic chips are lengthy, time-consuming, and require a super-clean environment. Chip bonding is difficult, the materials are fragile and costly. Due to these disadvantages, high molecular polymers have become important alternative materials for fabricating microfluidic chips. Polydimethylsiloxane (PDMS) is a silicone elastomer that can transmit ultraviolet and visible light above 300 nm. It has the characteristics of non-toxicity, low cost, easy availability, good flexibility, low polymerization temperature, the ability to replicate microchannels by casting method, simple and rapid processing, and low chip cost. It is a polymer material widely used in the preparation of microfluidic analysis chips at present.

[0003] However, PDMS has natural high hydrophobicity and adsorption of non-polar substances, which greatly limits its further application in the field of microfluidic technology. It is very important to modify and decorate the surface of PDMS. The hydrophilic modification of PDMS has always been a difficult problem. Although there are many studies on the hydrophilic modification of PDMS at present, there are certain restrictions and inconveniences. For example, hydrophilic modification of the substrate by plasma technology is relatively common. This modification method does not require the use of organic reagents and will not cause pollution. However, the obtained hydrophilic surface is unstable and will gradually recover hydrophobicity in a short time, and it cannot last. Moreover, plasma equipment is relatively expensive.

[0004] The ultraviolet ozone radiation treatment method is milder than the plasma treatment method and causes less damage to the PDMS surface, but it takes a longer time and has stricter requirements for the experimental environment. Grafting active molecules or polymers onto the PDMS surface through chemical grafting is an effective method for hydrophilic modification, with high synthetic flexibility. For example, the surface of PDMS can be silanized, aminated, grafted with PEG, HEMA, HA, etc. However, the grafting efficiency, the maintenance time of hydrophilicity after grafting, as well as the complexity of the grafting process, the use of harmful reagents and expensive catalysts are issues that have to be considered. And the direct grafting effect is often not good, and it usually requires prior plasma treatment or ultraviolet irradiation of PDMS to activate it in order to improve the grafting efficiency and extend the maintainable time of the modified surface.

[0005] Patent CN116655987A discloses a method for hydrophilically treating the surface of a substrate. Coating a hydrophilic coating on the surface of PDMS is a more economical method. That is, by activating the hydrophobic substrate to make its surface carry active groups, and covering the prepared hydrophilic polymer on the surface of the substrate, so that it undergoes a cross-linking reaction with the active groups to form a hydrophilically modified layer with chemical bonding, thereby obtaining a hydrophilically modified substrate surface. This method has more durability and wash resistance than existing modification techniques, but there are also disadvantages such as the long time-consuming process of preparing the hydrophilic polymer and the cross-linking reaction, and the operation is relatively cumbersome.

[0006] Therefore, how to conveniently and efficiently hydrophilically modify PDMS and make it have long-term stability is still a difficult point, which requires more exploration and development and has become a technical problem that needs to be solved urgently at present. Summary of the Invention

[0007] In order to solve the above problems, the present invention provides a simple and effective method for hydrophilically modifying PDMS and PDMS with a hydrophilic coating after modification. The surface of PDMS after hydrophilic modification treatment has a long stable time, and this modification method is simple, effective and low-cost.

[0008] Specifically, the present invention provides a simple and effective method for hydrophilically modifying PDMS, including the following steps:

[0009] 1) Add a certain amount of surfactant and binder to an alcohol solution, and stir until completely dissolved;

[0010] 2) Add TiO2 powder to the solution obtained in step 1), and stir until fully mixed;

[0011] 3) Then drop a silane surface modifier into the above solution, continue to stir and ultrasonicate to obtain a uniformly mixed solution;

[0012] 4) Use the uniformly mixed solution prepared in step 3) to construct a hydrophilic coating on the surface of the PDMS substrate, remove the excess solvent, and dry it to obtain hydrophilically modified PDMS.

[0013] In an embodiment of the present invention, the alcohol solution in step 1) is an aqueous solution of ethanol, where V 乙醇 :V 水 =(20 - 50):1.

[0014] In an embodiment of the present invention, the surfactant and binder are polyethylene glycol (PEG); the mass ratio of the polyethylene glycol to the alcohol solution is 1:(50 - 200), preferably 1:(80 - 120).

[0015] For example, 1:80, 1:90, 1:100, 1:110, 1:120, or any point value within the above numerical range.

[0016] In one embodiment of the present invention, the powder particle size of the TiO2 powder is 5 - 50 nm; preferably 10 - 20 nm.

[0017] For example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm.

[0018] In one embodiment of the present invention, the mass ratio of the TiO2 powder to the alcohol solution is 1:(10 - 50), preferably 1:(15 - 25).

[0019] In one embodiment of the present invention, the silane surface modifier is an alkoxysilane, and the alkoxysilane has one or more active groups such as aminopropyl, epoxy group, amide group, and vinyl group.

[0020] For example, one or more selected from (3 - aminopropyl)trimethoxysilane, (3 - aminopropyl)triethoxysilane, tetraethoxysilane, N-(3 - triethoxysilylpropyl)-4 - hydroxybutyramide silane, and 2-(3,4 - epoxycyclohexyl)ethyltrimethoxysilane.

[0021] In one embodiment of the present invention, after dropping the surface modifier in step 3), stirring is continued for 30 - 90 min, and ultrasonic treatment is carried out for 15 - 25 min.

[0022] In one embodiment of the present invention, in step 4), a hydrophilic coating is constructed by spin - coating or dip - coating with the mixed solution.

[0023] Preferably, when using the spin - coating process, the rate is 100 - 10000 rad / min, and the dip - coating time is 3 - 5 min.

[0024] Preferably, when using the dip - coating process, the speed is 10 - 30 mm / min, and the dip - coating time is 1 - 5 min.

[0025] In one embodiment of the present invention, before constructing the hydrophilic coating on the PDMS substrate surface, it further includes a step of pre - cleaning the PDMS substrate, including ultrasonic cleaning with absolute ethanol and deionized water, and drying with nitrogen.

[0026] In one embodiment of the present invention, after removing the excess solvent in step 4), it is naturally air - dried, and then placed in an oven at 100 - 120 °C for baking for 5 - 10 h.

[0027] The present invention also provides a PDMS with a hydrophilic modified coating, which is obtained by the above - mentioned hydrophilic modification method.

[0028] Preferably, the water contact angle of the PDMS with the hydrophilic modified coating is less than 10°.

[0029] Advantages of the present invention:

[0030] The PDMS hydrophilic modification method provided by the present invention uses an alcohol solution, a surfactant, and a binder to be mixed evenly, and then constructs a hydrophilic coating on the surface of PDMS through simple spin coating or dip coating techniques. Plasma treatment or ultraviolet irradiation is not required. By adding a silane modifier, the aggregation of titanium dioxide particles can be reduced. By adding polyethylene glycol, the surface of the obtained hydrophilic film can be made more uniform and smooth, thereby ensuring that titanium dioxide is more evenly coated on the substrate surface. The hydrophilic surface of the treated PDMS has a long stable time. After testing, the water contact angle is basically less than 10 °C, and even lower than 7 °C. This method is simple, effective, and low-cost, and no expensive or toxic chemical reagents are required during the modification process. Description of the drawings

[0031] Figure 1 Schematic diagram for measuring the contact angle of the un-hydrophilic modified PDMS substrate in Comparative Example 1;

[0032] Figure 2 Schematic diagram for measuring the contact angle of the PDMS hydrophilically modified by the method of the present invention in Example 1. Detailed implementation manners

[0033] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be emphasized that the specific embodiments described here are only for better explaining the present invention, and are partial embodiments of the present invention, not all embodiments, so they are not used to limit the present invention. In addition, the technical features involved in the embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Example 1

[0035] 1) Add 0.2 g of polyethylene glycol to 20 mL of ethanol solution (ethanol: water = 20:1), and stir until completely dissolved. Add 1 g of TiO2 with a particle size of 10 nm to the above solution, and stir vigorously for 30 min to make it fully mixed. Add 0.002 mol / L (3-aminopropyl) trimethoxysilane modifier solution to the mixed solution, continue to stir for 30 min, and ultrasonicate for 30 min to make the solution evenly mixed to obtain a hydrophilic mixed solution.

[0036] 2) Ultrasonically clean the PDMS with absolute ethanol for 1 min * 3 times, then rinse with deionized water, ultrasonicate for 5 min, and dry with nitrogen.

[0037] 3) Spin-coat the prepared hydrophilic mixture on the surface of the PDMS substrate at a speed of 1000 rad / min, remove the excess solvent and let it air-dry naturally, then bake it in an oven at 110 °C for 5 h to obtain the surface of the PDMS substrate modified with a hydrophilic coating.

[0038] Perform a water contact angle test on the surface of the PDMS substrate modified with a hydrophilic coating. Compare it with the PDMS substrate without hydrophilic modification, and conduct tests respectively after 1 day, 7 days, one month, and three months of placement to explore its hydrophilic retention.

[0039] Example 2

[0040] 1) Add 0.3 g of polyethylene glycol to 30 mL of an ethanol solution (ethanol: water = 30:1), and stir until completely dissolved. Add 1.5 g of TiO₂ with a particle size of 10 nm to the above solution, and stir vigorously for 30 min to mix it thoroughly. Add 0.002 mol / L (3-aminopropyl)triethoxysilane modifier solution to the mixture, continue to stir for 30 min and sonicate for 30 min to make the solution mix evenly, obtaining a hydrophilic mixture.

[0041] 2) Ultrasonically clean the PDMS with anhydrous ethanol for 1 min * 3 times, then rinse it with deionized water, sonicate for 5 min, and dry it with nitrogen.

[0042] 3) Spin-coat the prepared hydrophilic mixture on the surface of the PDMS substrate at a speed of 1000 rad / min, remove the excess solvent and let it air-dry naturally, then bake it in an oven at 100 °C for 10 h to obtain the surface of the PDMS substrate modified with a hydrophilic coating.

[0043] Perform a water contact angle test on the surface of the PDMS substrate modified with a hydrophilic coating. Compare it with the PDMS substrate without hydrophilic modification, and conduct tests respectively after 1 day, 7 days, one month, and three months of placement to explore its hydrophilic retention.

[0044] Example 3

[0045] 1) Add 0.2 g of polyethylene glycol to 20 mL of an ethanol solution (ethanol: water = 20:1), and stir until completely dissolved. Add 1 g of TiO₂ with a particle size of 20 nm to the above solution, and stir vigorously for 30 min to mix it thoroughly. Add 0.003 mol / L tetraethoxysilane modifier solution to the mixture, continue to stir for 30 min and sonicate for 30 min to make the solution mix evenly, obtaining a hydrophilic mixture.

[0046] 2) Ultrasonically clean the PDMS with anhydrous ethanol for 1 min * 3 times, then rinse it with deionized water, sonicate for 5 min, and dry it with nitrogen.

[0047] 3) Dip the above-prepared hydrophilic mixture onto the substrate surface at a speed of 20 mm / min for 2 min. After removing the excess solvent, air-dry it naturally, and then bake it in an oven at 120 °C for 5 h to obtain the substrate surface modified with a hydrophilic coating.

[0048] Perform water contact angle tests on the PDMS substrate surfaces modified with hydrophilic coatings in Examples 1-3, and compare them with the unmodified PDMS substrate in Comparative Example 1. Test and explore their hydrophilic retention after 1 day, 7 days, one month, and three months of placement.

[0049] Table 1. Test results of hydrophilic retention

[0050] Processing completed 1 day 7 days One month Three months Comparative Example 1 115° - - - - Example 1 10° 10° 10° 10° 11° Example 2 7° 7° 7° 7° 7° Example 3 8° 8° 8° 9° 9°

[0051] Figure 1 It is a contact angle measurement diagram of the unmodified PDMS substrate in Comparative Example 1. It can be seen that the unmodified PDMS surface shows a hydrophobic state. Figure 2 It is a contact angle measurement diagram of the PDMS after hydrophilic modification in Example 1. It can be seen that the water contact angle is greatly reduced compared with that before modification, and the hydrophilic modification achieves a good effect.

[0052] It can be seen that by using the PDMS hydrophilic modification method of the present invention, a hydrophilic coating can be constructed on the PDMS surface only through simple spin-coating or dip-coating techniques. After testing, the water contact angles are all less than 10 °C, and even lower than 7 °C. Perform hydrophilic retention tests on it, and the results are shown in Table 1. It can be seen that the PDMS hydrophilic surface treated by this method can have a long stable time.

[0053] The above are only the preferred application embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for hydrophilic modification of PDMS, characterized in that, It includes the following steps: 1) Add a certain amount of surfactant and binder into an alcohol solution, and stir until completely dissolved; 2) Add TiO2 powder into the solution obtained in step 1), and stir until fully mixed; 3) Then, dropwise add a silane surface modifier into the above solution, continue to stir, and perform ultrasonic treatment to obtain a uniformly mixed solution; 4) Use the uniformly mixed solution prepared in step 3) to construct a hydrophilic coating on the surface of the PDMS substrate, remove the excess solvent, and dry it to obtain hydrophilically modified PDMS.

2. The hydrophilic modification method according to claim 1, wherein The alcohol solution in step 1) is an aqueous solution of ethanol, where V 乙醇 :V 水 =(20 - 50):

1.

3. The hydrophilic modification method according to claim 1 or 2, characterized in that, The surfactant and binder are polyethylene glycol; the mass ratio of the polyethylene glycol to the alcohol solution is 1:(50 - 200), preferably 1:(80 - 120).

4. The hydrophilic modification method according to any one of claims 1 to 3, characterized in that, The powder particle size of the TiO2 powder is 5 - 50 nm; preferably 10 - 20 nm. Preferably, the mass ratio of the TiO2 powder to the alcohol solution is 1:(10 - 50), preferably 1:(15 - 25).

5. The hydrophilic modification method according to any one of claims 1 to 4, characterized in that, The silane surface modifier is an alkoxysilane, and the alkoxysilane has one or more active groups such as aminopropyl, epoxy group, amide group, and vinyl; Preferably, the silane surface modifier is selected from one or more of (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, tetraethoxysilane, N-(3-triethoxysilylpropyl)-4-hydroxybutyramide silane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

6. The hydrophilic modification method according to claim 1, wherein In step 3), after dropping the surface modifier, continue to stir for 30 - 90 min and perform ultrasonic treatment for 15 - 25 min.

7. The hydrophilic modification method according to claim 1, characterized in that, In step 4), the hydrophilic coating is constructed by spin coating or dip coating with the mixed solution; Preferably, when using the spin coating process, the rate is 100 - 10000 rad / min, and the dip coating time is 3 - 5 min; Preferably, when using the dip coating process, the speed is 10 - 30 mm / min, and the dip coating time is 1 - 5 min.

8. The hydrophilic modification method according to claim 1, wherein, Before constructing the hydrophilic coating on the surface of the PDMS substrate, it also includes a step of pre-cleaning the PDMS substrate, including ultrasonic cleaning with absolute ethanol and deionized water, and drying with nitrogen.

9. The hydrophilic modification method according to claim 1, wherein In step 4), after removing the excess solvent, air dry it naturally, and then place it in an oven at 100 - 120 °C for baking for 5 - 10 h.

10. A PDMS with a hydrophilic modified coating after modification, characterized in that, It is obtained by using the hydrophilic modification method described in any one of claims 1 to 9; Preferably, the water contact angle of the PDMS with the hydrophilic coating after modification is less than 10°.

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