Thin film, digital micro-fluidic chip substrate and preparation method of digital micro-fluidic chip substrate

Abstract

The invention relates to a thin film, a digital micro-fluidic chip substrate and a preparation method thereof. The film (3) is a dielectric hydrophobic film, one side of the dielectric hydrophobic film is a hydrophilic surface, and the other side of the dielectric hydrophobic film is a hydrophobic surface. The film (3) has dielectric and hydrophobic functions, thereby fundamentally overcoming the defect that the hydrophobic layer of the traditional digital micro-fluidic chip falls off from the dielectric layer to cause difficult-to-reverse damage to the chip, and greatly simplifying the preparation process of the dielectric hydrophobic layer. Meanwhile, the dielectric hydrophobic film has a hydrophilic surface, the hydrophilic surface can be firmly attached to the upper surface of the circuit substrate (1) after being combined with the adhesive (2), and the dielectric hydrophobic film is resistant to high temperature and not prone to falling off from the circuit substrate (1), so that the use environment of the chip is widened, and the service life of the chip is prolonged.

Description

A thin film, a digital microfluidic chip substrate and preparation method thereof

[0001] This application claims priority to Chinese patent application CN202210969277.X filed on August 12, 2022. The contents of that application are considered part of this application and are incorporated into this application as a whole. Technical Field

[0002] The present application belongs to the technical field of digital microfluidic chips, and specifically relates to a thin film, a digital microfluidic chip substrate and a preparation method thereof. Background Art

[0003] Digital microfluidic chips are based on electrowetting technology, which regulates the surface energy of solids and liquids through electric potential and exploits the asymmetry of the droplet contact angle to generate tangential thrust. This creates asymmetric deformation at both ends of the droplet, prompting a pressure difference within the droplet, thereby achieving precise manipulation of microfluidics. The basic components of a digital microfluidic chip include a circuit substrate, with a dielectric layer and a hydrophobic layer positioned above the circuit substrate, forming the chip base. The dielectric and hydrophobic layers above the circuit substrate are the most critical structures of the digital microfluidic chip, and their dielectric and hydrophobic properties are crucial for liquid manipulation.

[0004] Currently, the primary method for preparing digital microfluidic chip substrates involves first forming a dielectric layer material on top of a printed circuit board (PCB) through a coating process, and then forming a hydrophobic layer on top of the dielectric layer through processes such as spin coating or spray coating. The traditional preparation process is complex, and the dielectric film material suitable for the coating process is relatively thick, making it difficult to provide sufficient driving force for the liquid. Furthermore, the preparation of the hydrophobic layer requires high equipment and environmental cleanliness, resulting in high economic costs. Furthermore, the hydrophobic layer easily falls off the dielectric layer, causing irreversible damage to the digital microfluidic chip.

[0005] Summary of the Invention

[0006] In order to address the deficiencies in the prior art, the inventors have, after long-term exploration and continuous attempts, provided a film, a digital microfluidic chip substrate and a preparation method thereof. The film of the present application realizes the dual functions of a dielectric layer and a hydrophobic layer, fundamentally solving the problem that the hydrophobic layer is easily detached from the dielectric layer. At the same time, the dielectric hydrophobic film of the present application has a hydrophilic surface, which is conducive to combining with an adhesive, can be firmly attached to the upper surface of the circuit substrate, has the effect of withstanding high temperatures and not easily detaching from the circuit substrate, greatly broadening the use environment of the chip and extending the service life of the chip.

[0007] In a first aspect, the present application provides a film, wherein the film is a dielectric hydrophobic film, one side of the dielectric hydrophobic film is a hydrophilic side, and the other side is a hydrophobic side.

[0008] In a second aspect, the present application provides a digital microfluidic chip substrate, wherein the chip substrate comprises a circuit substrate, an adhesive and a film as described in the present application.

[0009] In a third aspect, the present application provides a method for preparing the film as described in the present application, wherein the method comprises performing surface modification treatment on the film.

[0010] In a fourth aspect, the present application provides a method for preparing a digital microfluidic chip substrate as described in the present application, wherein the method comprises:

[0011] (1) applying the adhesive on the surface of the circuit substrate;

[0012] (2) Laying the hydrophilic surface of the film on the surface of the adhesive.

[0013] In a fifth aspect, the present application provides the use of the film described in the present application to replace the dielectric layer and the hydrophobic layer in the preparation of a digital microfluidic chip.

[0014] In a sixth aspect, the present application provides a digital microfluidic chip, which comprises the film as described in the present application or the digital microfluidic chip substrate as described in the present application.

[0015] In a seventh aspect, the present application provides a digital microfluidic system, which comprises the film as described in the present application, or the digital microfluidic chip substrate as described in the present application, or the digital microfluidic chip as described in the present application.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The film described in the present application has the dual functions of the dielectric layer and the hydrophobic layer in the traditional process. It fundamentally solves the problem that the hydrophobic layer is easy to fall off from the dielectric layer, thereby causing irreversible damage to the digital microfluidic chip while greatly simplifying the preparation process, reducing production costs, and improving production efficiency. At the same time, compared with the film thickness of the traditional dielectric layer, the film of the present application has a thinner thickness, which provides a greater driving force while not being easily broken down by high voltage due to its thin thickness. The film described in the present application also has a hydrophilic surface. After the hydrophilic surface is combined with an adhesive, it can be firmly attached to the upper surface of the circuit substrate, has the effect of withstanding high temperatures of up to 100°C and is not easy to fall off from the circuit substrate, which greatly broadens the use environment of the chip and extends the service life of the chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a schematic diagram of the preparation of the digital microfluidic chip substrate described in this application.

[0019] Among them, 1-circuit substrate; 2-adhesive; 3-film. DETAILED DESCRIPTION

[0020] Unless otherwise indicated, all numbers used in this specification and claims to represent content, concentration, ratio, mass, percentage, technical effect, etc. should be understood as being modified by the term "about" or "approximately" under any circumstances. Therefore, unless otherwise indicated, the numerical parameters listed in the following specification and the appended claims are approximate values. Unless otherwise indicated, the terms used herein have the usual understanding meanings for those skilled in the art. For those skilled in the art, it can vary according to the desired properties and effects sought to be obtained through this application, and each numerical parameter should be interpreted according to the number of significant digits and conventional rounding methods or in a manner understood by those skilled in the art.

[0021] Although the numerical ranges and parameters setting forth the broad scope of this application are approximations, the numerical values ​​set forth in the specific examples are provided as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in its respective testing measurements. Every numerical range given herein will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were expressly written herein.

[0022] Unless otherwise specified, the orientations or positional relationships indicated by “center,” “longitudinal,” “lateral,” “up,” “down,” “front,” “back,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inside,” “outside,” etc. used in this specification and claims are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting this application. In addition, the terms “first,” “second,” etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as “first,” “second,” etc. may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, “multiple” means two or more.

[0023] In this application, the term "contact angle" refers to the angle between the solid-liquid interface, through the interior of the liquid, and the gas-liquid interface at the interface of solid, liquid, and gas. The contact angle is an important parameter for characterizing the wettability of a material surface. A contact angle of 0 indicates complete wetting; a contact angle less than 90° indicates partial wetting; a contact angle of 90° is the dividing line between wetting and non-wetting; a contact angle greater than 90° indicates non-wetting; and a contact angle of 180° indicates complete non-wetting. The contact angles of the films of this application were measured using a contact angle measuring instrument and image analysis.

[0024] In this application, the term "sliding angle" refers to the critical angle between the inclined surface and the horizontal plane at which a droplet just begins to roll. The sliding angle is an important parameter for characterizing the wettability of a material surface. The sliding angle of the films described herein was measured using an image analysis method using a sliding angle measuring instrument.

[0025] In a first aspect of the present application, a film is provided, wherein the film is a dielectric hydrophobic film, one side of the dielectric hydrophobic film is a hydrophilic side, and the other side is a hydrophobic side.

[0026] In some embodiments of the present application, the film is a single-layer film.

[0027] The film provided by this application achieves the dual functions of a dielectric layer and a hydrophobic layer in traditional processes, fundamentally resolving the problem of irreversible damage to digital microfluidic chips caused by the hydrophobic layer easily falling off the dielectric layer. Furthermore, the film provided by this application has stable performance and good chemical and biological compatibility, and has promising application prospects in the biochemical field. Furthermore, the film provided by this application has a hydrophilic surface that, when combined with an adhesive, can be firmly attached to the upper surface of a circuit substrate, making it less likely to fall off the circuit substrate, thereby significantly extending the service life of the chip.

[0028] In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is less than 90°.

[0029] In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is ≤80°. In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is ≤70°. In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is ≤60°. In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is ≤50°. In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is ≤40°. In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is ≤30°. In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is ≤20°. In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is ≤10°. In some embodiments of the present application, the contact angle of the hydrophilic surface of the film is 70°, 71°, 72°, 73°, 74° or 75°.

[0030] In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is ≥30°.

[0031] In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is 30°, 31°, 32°, 34° or 35°.

[0032] In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is ≥40°. In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is ≥50°. In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is ≥55°. In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is ≥60°. In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is ≥65°. In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is ≥70°.

[0033] In some embodiments of the present application, the dielectric hydrophobic film is a Teflon film.

[0034] In some embodiments of the present application, the film is an amorphous fluoropolymer film (AF), a fluorinated ethylene propylene resin film (FEP), a fluoropolymer foam resin film (FFR), a fluoropolymer resin film (NXT) or a perfluoroalkoxy resin film (PFA).

[0035] In some embodiments of the present application, the film is a fluorinated ethylene propylene resin film (FEP) or a perfluoroalkoxy resin film (PFA).

[0036] In some embodiments of the present application, the film is a fluorinated ethylene propylene resin film (FEP). In some embodiments of the present application, the film is a perfluoroalkoxy resin film (PFA).

[0037] In some embodiments of the present application, the thickness of the film is 5-200 μm.

[0038] In some embodiments of the present application, the thickness of the film is 5-150 μm.

[0039] In some embodiments of the present application, the thickness of the film is 10-100 μm. In some embodiments of the present application, the thickness of the film is 10-90 μm. In some embodiments of the present application, the thickness of the film is 10-80 μm. In some embodiments of the present application, the thickness of the film is 10-70 μm. In some embodiments of the present application, the thickness of the film is 10-60 μm. In some embodiments of the present application, the thickness of the film is 10-50 μm. In some embodiments of the present application, the thickness of the film is 10-40 μm. In some embodiments of the present application, the thickness of the film is 10-30 μm. In some embodiments of the present application, the thickness of the film is 10 μm, 12 μm, 12.5 μm, 15 μm, 20 μm, 25 μm or 30 μm. In some embodiments of the present application, the thickness of the film is 10-20 μm. In some embodiments of the present application, the thickness of the film is 12-18 μm. In some embodiments of the present application, the film has a thickness of 12-16 μm. In some embodiments of the present application, the film has a thickness of 12-14 μm. In some embodiments of the present application, the film has a thickness of 12 μm, 12.5 μm, 13 μm, 13.5 μm, or 14 μm.

[0040] In some embodiments of the present application, the thickness of the film is 12.5-25 μm.

[0041] In some embodiments of the present application, the thickness of the film is 12.5 μm or 25 μm.

[0042] In order to provide sufficient driving force for the liquid, the thickness of the dielectric layer and the hydrophobic layer needs to be reduced. However, in the traditional preparation process of the dielectric layer, in order to be applicable to the coating process, the thickness of the dielectric material cannot be too low. At the same time, the dielectric layer thickness is too low and is easily broken down by high voltage, resulting in damage to the chip. The film described in the present application has a film thickness far lower than that of the dielectric layer prepared by the traditional process, which can provide sufficient driving force for the liquid. At the same time, the film described in the present application has a higher breakdown voltage and is not easily broken down.

[0043] In a second aspect of the present application, a digital microfluidic chip substrate is provided, wherein the chip substrate comprises a circuit substrate, an adhesive and the film as described in the present application.

[0044] In some embodiments of the present application, referring to FIG. 1 , the chip substrate includes the circuit substrate 1 , the adhesive 2 , and the film 3 .

[0045] In some embodiments of the present application, there is no particular limitation on the material of the circuit substrate, and a commonly used circuit substrate in the art can be used. In some embodiments of the present application, the circuit substrate is a copper clad laminate, a ceramic substrate, or an aluminum substrate.

[0046] In some embodiments of the present application, the circuit substrate and the film are bonded via the adhesive, and the adhesive is combined with the hydrophilic surface of the film.

[0047] In some embodiments of the present application, the upper surface of the circuit substrate is covered with the adhesive, and the other side of the adhesive is bonded to the hydrophilic surface of the film.

[0048] In some embodiments of the present application, the adhesive comprises one or more of polyacrylic acid, polyurethane, epoxy resin, polyimide, polystyrene, polyacrylate or ethylene-vinyl acetate copolymer. In some embodiments of the present application, the adhesive is one or more of polyacrylic acid, polyurethane or epoxy resin.

[0049] In some embodiments of the present application, the thickness of the adhesive is 1-50 μm. In some embodiments of the present application, the thickness of the adhesive is 5-40 μm. In some embodiments of the present application, the thickness of the adhesive is 5-30 μm. In some embodiments of the present application, the thickness of the adhesive is 5-25 μm. In some embodiments of the present application, the thickness of the adhesive is 5-20 μm. In some embodiments of the present application, the thickness of the adhesive is 5-15 μm. In some embodiments of the present application, the thickness of the adhesive is 5-10 μm.

[0050] The third aspect of the present application provides a method for preparing the film as described in the present application, the method comprising performing surface modification treatment on the film.

[0051] In some embodiments of the present application, the film is subjected to surface modification to obtain the hydrophilic surface, and the contact angle of the hydrophilic surface is less than 90°.

[0052] In some embodiments of the present application, the contact angle of the hydrophilic surface is ≤80°. In some embodiments of the present application, the contact angle of the hydrophilic surface is ≤70°. In some embodiments of the present application, the contact angle of the hydrophilic surface is ≤60°. In some embodiments of the present application, the contact angle of the hydrophilic surface is ≤50°. In some embodiments of the present application, the contact angle of the hydrophilic surface is ≤40°. In some embodiments of the present application, the contact angle of the hydrophilic surface is ≤30°. In some embodiments of the present application, the contact angle of the hydrophilic surface is ≤20°. In some embodiments of the present application, the contact angle of the hydrophilic surface is ≤10°. In some embodiments of the present application, the contact angle of the hydrophilic surface is 70°, 71°, 72°, 73°, 74° or 75°.

[0053] In some embodiments of the present application, the film is surface modified to obtain the hydrophilic surface, and the sliding angle of the hydrophilic surface is ≥30°.

[0054] In some embodiments of the present application, the sliding angle of the hydrophilic surface of the film is 30°, 31°, 32°, 34° or 35°.

[0055] In some embodiments of the present application, the rolling angle of the hydrophilic surface is ≥40°. In some embodiments of the present application, the rolling angle of the hydrophilic surface is ≥50°. In some embodiments of the present application, the rolling angle of the hydrophilic surface is ≥55°. In some embodiments of the present application, the rolling angle of the hydrophilic surface is ≥60°. In some embodiments of the present application, the rolling angle of the hydrophilic surface is ≥65°. In some embodiments of the present application, the rolling angle of the hydrophilic surface is ≥70°.

[0056] In some embodiments of the present application, the surface modification treatment is corona treatment, plasma treatment, chemical treatment, surface grafting treatment or photochemical modification treatment.

[0057] In some embodiments of the present application, the surface modification treatment is corona treatment, plasma treatment or chemical treatment.

[0058] In some embodiments of the present application, the surface modification treatment is corona treatment. The corona treatment described in the present application is an electric shock treatment, specifically, a corona treatment machine is used to perform corona discharge on the film surface using high frequency and high voltage to generate low temperature plasma to enhance the film surface adhesion.

[0059] In some embodiments of the present application, the plasma treatment is low-temperature plasma treatment, specifically, applying sufficient energy to the gas to ionize the gas into a plasma state, and then treating the film surface with the low-temperature plasma.

[0060] In some embodiments of the present application, the chemical treatment may be a chemical oxidation treatment, specifically a treatment with an oxidant before the film is used.

[0061] In some embodiments of the present application, the surface grafting treatment may be to form hydrophilic groups on the surface of the film. In some embodiments of the present application, the surface grafting treatment may be to graft hydrophilic molecules on the surface of the film.

[0062] In a fourth aspect of the present application, a method for preparing a digital microfluidic chip substrate as described in the present application is provided, the method comprising:

[0063] (1) applying the adhesive on the surface of the circuit substrate;

[0064] (2) Laying the hydrophilic surface of the film on the surface of the adhesive.

[0065] In some embodiments of the present application, the method further comprises, in step (2), coating the hydrophobic surface of the film with a protective film.

[0066] In some embodiments of the present application, the method further comprises:

[0067] (3) processing the thin film on the surface of the circuit substrate in step (2) to obtain a desired shape;

[0068] (4) removing the protective film to obtain the digital microfluidic chip substrate.

[0069] In some embodiments of the present application, in step (1), it further includes first cleaning the surface of the circuit substrate and then applying the adhesive on the surface of the circuit substrate.

[0070] In some embodiments of the present application, there is no particular limitation on the cleaning solvent for the circuit substrate surface, as long as no residue remains on the circuit substrate surface after cleaning. In some embodiments of the present application, the cleaning solvent includes one or more of isopropyl alcohol, ethanol, dimethylformamide, methyl pyrrolidone, or dipropylene glycol dimethyl ether.

[0071] In some embodiments of the present application, in step (1), the coating process is a screen printing process. In some embodiments of the present application, in step (1), the coating process may also be to first apply the adhesive to the surface of the circuit substrate, and then use a roller pressing method to evenly cover the adhesive on the surface of the circuit substrate.

[0072] In some embodiments of the present application, in step (2), the hydrophobic surface of the film is first coated with a protective film, and then the hydrophilic surface of the film is coated on the surface of the adhesive. In some embodiments of the present application, in step (2), the hydrophilic surface of the film is first coated on the surface of the adhesive, and then the hydrophobic surface of the film is coated with a protective film.

[0073] In some embodiments of the present application, there are no particular limitations on the protective film, as long as it provides sufficient support for the film and facilitates subsequent manipulation of the film. In some embodiments of the present application, the protective film comprises one or more of a polyethylene terephthalate film (PET film) or a polyvinyl chloride film (PVC film). In some embodiments of the present application, the protective film is a PET film.

[0074] In some embodiments of the present application, the order of step (2) and step (3) can be interchanged. In some embodiments of the present application, the hydrophobic surface of the film can be coated with a protective film, and the film coated with the protective film can be processed to obtain a film with a target shape, and finally the hydrophilic surface of the film with the target shape can be coated on the adhesive surface.

[0075] In some embodiments of the present application, in step (3), the processing method is a method commonly used in the art to process a film to obtain a target shape. In some embodiments of the present application, in step (3), the processing method is laser engraving, punching, or die cutting.

[0076] In some embodiments of the present application, in step (4), the protective film is removed after the adhesive is cured. In some embodiments of the present application, the adhesive cures for 5-60 seconds. In some embodiments of the present application, the adhesive cures for 10-50 seconds. In some embodiments of the present application, the adhesive cures for 10-40 seconds. In some embodiments of the present application, the adhesive cures for 10-30 seconds. In some embodiments of the present application, the adhesive cures for 10-20 seconds. In some embodiments of the present application, the adhesive cures for 15 seconds.

[0077] The fifth aspect of the present application provides the use of the film described in the present application in place of a dielectric layer and a hydrophobic layer in the preparation of a digital microfluidic chip.

[0078] In a sixth aspect of the present application, a digital microfluidic chip is provided, wherein the digital microfluidic chip comprises the film as described in the present application or the digital microfluidic chip substrate as described in the present application.

[0079] In some embodiments of the present application, the digital microfluidic chip has a three-layer structure, specifically an upper electrode plate, a lower electrode plate and a cavity between the upper and lower electrodes for the movement of the test liquid. The lower electrode plate includes a circuit substrate, a microelectrode array and the film described in this application. The filling material between the upper and lower electrodes can be air or silicone oil.

[0080] In some embodiments of the present application, the digital microfluidic chip adopts a coplanar electrode design, has no upper plate structure, and both positive and negative electrodes are arranged on the lower plate, which includes a circuit substrate, a microelectrode array and the film described in this application.

[0081] In a seventh aspect of the present application, the present application provides a digital microfluidic system, which comprises the film as described in the present application or the digital microfluidic chip substrate as described in the present application or the digital microfluidic chip as described in the present application.

[0082] In some embodiments of the present application, the digital microfluidic system may include a sample injection system, a nucleic acid extraction system, a detection system, a reaction system, etc., but is not limited thereto.

[0083] The various embodiments and preferences described above for the thin film, digital microfluidic chip substrate and preparation method thereof of the present application can be combined with each other (as long as they are not inherently contradictory to each other), and the various embodiments formed by such combinations are considered to be part of the disclosure of this application.

[0084] The following examples will be used to more clearly and specifically illustrate the technical solutions of this application. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of protection of this application. The scope of protection of this application is defined solely by the claims.

[0085] Example

[0086] Unless otherwise specified, the raw materials and instruments used in the examples are commercially available.

[0087] Example 1: Preparation of FEP film 1

[0088] (1) Put the FEP raw material particles into the drying equipment (STOLZ, CLK100), set the drying temperature to 60 ° C, and the cycle drying time to 4 h;

[0089] (2) After the drying, the raw materials were fed into the hopper of a film blowing equipment (VAREX II) through a vacuum pipeline and film blowing was performed under the conditions of a temperature of 260°C, a speed of 100 r / min, an air circulation current of 4 A, and a cooling water temperature of 5°C to obtain an FEP film with a thickness of 12.5 μm.

[0090] (3) corona treatment was performed on one side of a 12.5 μm FEP film using a corona device (AcXys Technologies, ULD 500) at 15,000 V, 25 kHz, and an electrode gap of 1 mm to obtain an FEP film 1 having a hydrophilic surface.

[0091] (4) The FEP film 1 is wound up by a winder for standby use.

[0092] Example 2: Preparation of PFA film 2

[0093] (1) PFA raw material pellets were placed in a drying equipment (STOLZ, CLK100), the drying temperature was set to 60°C, and the cycle drying time was 4 h;

[0094] (2) After the drying, the raw materials were fed into the hopper of a film blowing equipment (VAREX II) through a vacuum pipeline and film blowing was performed under the conditions of a temperature of 250°C, a speed of 100 r / min, an air circulation current of 4 A, and a cooling water temperature of 5°C to obtain a PFA film with a thickness of 12.5 μm.

[0095] (3) After the film blowing was completed, one side of the 12.5 μm PFA film was corona treated using a corona device (AcXys Technologies, ULD 500) at 15,000 V, 25 kHz, and an electrode gap of 1 mm to obtain a PFA film 2 having a hydrophilic surface.

[0096] (4) The PFA film 2 is wound up by a winder for standby use.

[0097] Example 3: Preparation of FEP film 3

[0098] (1) Put the FEP raw material particles into the drying equipment (STOLZ, CLK100), set the drying temperature to 60 ° C, and the cycle drying time to 4 h;

[0099] (2) After the drying, the raw materials were fed into the hopper of a film blowing equipment (VAREX II) through a vacuum pipeline, and film blowing was performed under the conditions of a temperature of 260°C, a speed of 50 r / min, an air circulation current of 4 A, and a cooling water temperature of 5°C to obtain an FEP film with a thickness of 25 μm;

[0100] (3) corona treatment was performed on one side of a 25 μm FEP film using a corona device (AcXys Technologies, ULD 500) at 15,000 V, 25 kHz, and an electrode gap of 1 mm to obtain an FEP film 3 having a hydrophilic surface;

[0101] (4) The FEP film 3 is wound up by a winder for standby use.

[0102] Example 4: Preparation of chip substrate 1

[0103] (1) Use isopropyl alcohol to clean the surface of the circuit board;

[0104] (2) The surface of the circuit substrate in step (2) is evenly coated with a layer of adhesive by screen printing, wherein the adhesive is polyacrylic acid and the printing thickness is 5-10 μm;

[0105] (3) coating the hydrophobic surface of the FEP film 1 with a layer of PET protective film;

[0106] (4) laminating the hydrophilic surface of the film of step (3) evenly on the circuit substrate printed with the adhesive of step (2) by a rolling process;

[0107] (5) placing the product of step (4) under a UV light source for 15 seconds to allow the adhesive to cure;

[0108] (6) Carving the target shape of the FEP film 1 on the surface of the circuit substrate by laser;

[0109] (7) The PET protective film on the hydrophobic surface of the FEP film 1 is removed to obtain the chip substrate 1.

[0110] Example 5: Preparation of chip substrate 2

[0111] The preparation method of the chip substrate 2 is the same as that of Example 4, with the only difference being that the FEP film 1 in step (3) is replaced by a PFA film 2.

[0112] Example 6: Preparation of chip substrate 3

[0113] The preparation method of the chip substrate 3 is the same as that of Example 4, with the only difference being that the FEP film 1 in step (3) is replaced by the FEP film 3.

[0114] Comparative Example 1

[0115] (1) Apply 25 μm KAPTON tape to the surface of the chip substrate as a dielectric layer;

[0116] (2) Spray CYTOP evenly on the upper surface of KAPTON tape;

[0117] (3) Place the chip substrate on a heating table and set the temperature to 90 degrees Celsius to vitrify the CYTOP;

[0118] (4) cooling the chip substrate to solidify the CYTOP as a hydrophobic layer, thereby obtaining a conventional chip substrate having a dielectric layer and a hydrophobic layer;

[0119] (5) After the chip substrate of step (4) was made into a chip, a pure water continuous flow test was conducted. Ten chips were tested. After 30 minutes of continuous pure water flow, three chips had the phenomenon of partial detachment of the hydrophobic layer of the chip substrate from the dielectric layer. The chip substrate 1 having a hydrophilic one side was used to make a pure water continuous flow test. Ten chips were tested using the chip substrate 1 having a hydrophilic one side. After 30 minutes of continuous pure water flow, none of the ten chips had partial detachment. The specific operation of the pure water continuous flow test is as follows: the chip cavity is filled with silicone oil and then a drop of 10 μL pure water is injected. The control electrodes are turned on in sequence to allow the droplet to circulate back and forth in the chip cavity for 30 minutes.

[0120] Comparative Example 2

[0121] The preparation method of the chip substrate of Comparative Example 2 is the same as that of Example 4, except that the FEP film 1 in step (3) is replaced by a 12.5 μm FEP film that has not been hydrophilically treated.

[0122] Comparative Example 3

[0123] The preparation method of the chip substrate of Comparative Example 3 is the same as that of Example 4, except that the FEP film 1 in step (3) is replaced by a 12.5 μm PFA film that has not been hydrophilically treated.

[0124] Performance Testing

[0125] 1. Measurement of film contact angle parameters

[0126] The contact angle of the film was measured using a contact angle meter (Shengding, SDC-350) to characterize the hydrophilicity of the hydrophilic surface of the film.

[0127] The performance and hydrophobicity of the hydrophobic surface were measured on 60 pieces. The following is the test process:

[0128] (1) Place the film on the test platform;

[0129] (2) Start the measuring instrument, drop 10μm purified water on the measuring position, and start the test;

[0130] (3) The measurement software runs automatically and outputs the contact angle value.

[0131] 2. Thin film dielectric constant measurement

[0132] The three-terminal method was used to test the dielectric constant of the film using an impedance meter (Wenko, WK6500B). The measurement process is as follows:

[0133] (1) Clamp the film sample onto a test fixture for holding dielectric materials in a measuring instrument;

[0134] (2) Place the two electrodes of the measuring instrument on the test fixture and start measuring;

[0135] (3) The impedance meter software program calculates the dielectric constant of the film.

[0136] 3. Thin film breakdown voltage measurement

[0137] The film breakdown voltage was measured using a voltage breakdown tester (Aino, AN96). The test process is as follows:

[0138] (1) Turn on the voltage breakdown tester and preheat for 15 minutes;

[0139] (2) Open the equipment door, place the film sample between the two electrodes, and close the equipment door;

[0140] (3) Set parameters in the tester software and start testing;

[0141] (4) The instrument software program outputs the voltage curve and breakdown voltage value.

[0142] 4. Thin film gas permeability measurement

[0143] Use differential pressure gas permeometer (Languang, VAC-V2) to measure the gas permeability of the film:

[0144] (1) Cut film samples and measure thickness;

[0145] (2) Apply a layer of vacuum grease on the test bench. If the grease is applied to the disc in the cavity, it should be wiped off carefully. If there is grease on the edge of the filter paper, the filter paper should be replaced (filter paper for chemical analysis, thickness 0.2-0.3 mm).

[0146] (3) Close the needle valves in the vent chamber and start the vacuum pump;

[0147] (4) Place the filter paper on the disc in the test bench and then place the state-conditioned sample on it. The sample should be kept flat and free of wrinkles. Press gently to ensure good contact between the sample and the vacuum grease on the test bench. Open the needle valve in the low-pressure chamber. The sample should fit tightly on the filter paper under vacuum. Place an O-ring in the groove of the upper cover, close the upper cover and tighten it;

[0148] (5) Open the needle valve and isolation valve of the high-pressure chamber, start vacuuming until the pressure is below 27 Pa, and continue degassing for more than 3 hours to remove the gas and water vapor adsorbed by the sample;

[0149] (6) Close the isolation valve, open the test gas cylinder and the gas source switch to fill the high-pressure chamber with test gas. The gas pressure in the high-pressure chamber should be (1.0~1.1)x10 5 Pa range. When the pressure is too high, the isolation valve should be opened to discharge;

[0150] (7) Turn on the host power switch and the computer power switch, and enter the name, thickness, low-pressure chamber volume parameters and test gas name of each test bench sample through the keyboard to prepare for the test;

[0151] (8) Close the high and low pressure chamber exhaust needle valves and start the air permeability test;

[0152] (9) To eliminate the nonlinear stage at the beginning of the test, a 10-minute pre-ventilation test should be conducted. Then the formal permeation test should be started, and the pressure change value ΔP of the low-pressure chamber and the test time t should be recorded;

[0153] (10) Continue the test until the pressure difference changes remain constant within the same time interval, achieving stable permeability. Take the pressure difference values ​​of at least three consecutive time intervals and calculate their arithmetic mean to calculate the gas permeation rate and gas permeability of the sample.

[0154] 5. Measurement of film temperature stability

[0155] Use film thermal shrinkage tester (Saicheng, RSY-01) to test the film temperature stability:

[0156] (1) Cut a 15mm*130mm film sample and punch holes at both ends of the sample with a hole spacing of 100mm and a hole diameter of 5mm;

[0157] (2) Clamp the sample to the clamps at both ends of the tester to ensure that the sample is flat;

[0158] (3) Turn on the instrument, set the temperature to 100°C, and start heating;

[0159] (4) The shrinkage rate of the film output by the test instrument in a 100°C environment is qualified if it is less than 0.8%.

[0160] 6. Chip substrate adhesion test

[0161] Use the Edelberg universal tensile and compressive tester to measure the chip substrate adhesion:

[0162] (1) Peel back the short side of the film on the chip substrate after lamination, clamp the film in the tester fixture perpendicular to the chip substrate, and tighten the screws to fix the film;

[0163] (2) Lower the tester until the chip substrate contacts the test platform;

[0164] (3) Fix the chip substrate on the test platform using a fixture;

[0165] (4) Start the test instrument, and the peak value of the output tensile force is the chip substrate bonding force.

[0166] 7. Film rolling angle parameter measurement

[0167] The film's rolling angle was measured using a rolling angle meter (Shengding, SDC-350) to characterize the hydrophilicity of the film's hydrophilic side and the hydrophobicity of the film's hydrophobic side. 60 films were measured. The test process is as follows:

[0168] (1) Place the coated chip substrate on the test platform;

[0169] (2) Start the measuring instrument, drop 10μm purified water on the measuring position, and start the test;

[0170] (3) The measurement software runs automatically and outputs the roll angle value.

[0171] Experimental results and discussion

[0172] Table 1 Statistical table of hydrophilic and hydrophobic properties of films of Examples 1 to 3

[0173] Table 2 Performance test parameters of Examples 4-6 and Comparative Examples 2-3

[0174] As can be seen from Tables 1 and 2, the films of Examples 1-3 exhibit good dielectric constants and large contact angles on the hydrophobic surface, achieving the dual functions of dielectric and hydrophobic layers in conventional processes. Furthermore, the films of Examples 1-3 exhibit high breakdown voltages, good gas permeabilities, and excellent temperature stability, remaining wrinkle-free even at temperatures of 100°C, demonstrating their wide applicability in a wide range of environments.

[0175] Comparative Example 1 shows that, while conventional chips with a dielectric layer and a hydrophobic layer are prone to partial detachment of the hydrophobic layer, the chip prepared using the film of the present application exhibits no partial detachment. Therefore, the film of the present application fundamentally addresses the problem of irreversible damage to digital microfluidic chips caused by the hydrophobic layer easily detaching from the dielectric layer. Furthermore, compared to traditional, complex preparation processes, the chip substrate preparation method of the present application is simple.

[0176] As shown in Table 1, the corona-treated side of the film has a rolling angle of 30°-35° and a contact angle of 70°-75°, indicating hydrophilicity. Examples 4-6 and Comparative Examples 2-3 demonstrate that, after hydrophilic treatment, the films of Examples 4-6 exhibit enhanced adhesion to the circuit substrate, allowing for secure adhesion to the upper surface of the circuit substrate. They are also less likely to fall off the circuit substrate, even after being soaked in solvents during use of the digital microfluidic chip, thereby extending the life of the chip.

Claims

1. A film, wherein The film is a dielectric hydrophobic film, one side of which is a hydrophilic surface, and the other side is a hydrophobic surface.

2. The film according to claim 1, wherein The contact angle of the hydrophilic surface of the film is less than 90°.

3. The film according to claim 1 or 2, wherein The sliding angle of the hydrophilic surface of the film is ≥30°.

4. The film according to any one of claims 1 to 3, wherein The dielectric hydrophobic film is a Teflon film.

5. The film according to claim 4, wherein The film is an amorphous fluoropolymer film, a fluorinated ethylene propylene resin film, a fluoropolymer foam resin film, a fluoropolymer resin film or a perfluoroalkoxy resin film.

6. The film according to claim 4 or 5, wherein The film is a fluorinated ethylene propylene resin film or a perfluoroalkoxy resin film.

7. The film according to any one of claims 1 to 6, wherein The thickness of the film is 5-200 μm.

8. The film according to claim 7, wherein The thickness of the film is 10-100 μm.

9. The film according to claim 8, wherein The thickness of the film is 12.5-25 μm.

10. The film according to claim 9, wherein The thickness of the film is 12.5 μm or 25 μm.

11. A digital microfluidic chip substrate, wherein: The chip substrate comprises a circuit substrate, an adhesive, and the film according to any one of claims 1 to 10.

12. The digital microfluidic chip substrate according to claim 11, wherein: The circuit substrate and the film are bonded together by the adhesive, and the adhesive is combined with the hydrophilic surface of the film.

13. The digital microfluidic chip substrate according to claim 11 or 12, wherein: The adhesive is one or more of polyacrylic acid, polyurethane, epoxy resin, polyimide, polystyrene, polyacrylate or ethylene-vinyl acetate copolymer.

14. A method for preparing the film according to any one of claims 1 to 10, wherein: The method comprises subjecting the film to surface modification treatment.

15. The method of claim 14, wherein: The film is subjected to surface modification to obtain the hydrophilic surface, and the contact angle of the hydrophilic surface is less than 90°.

16. The method according to claim 14 or 15, wherein: The film is subjected to surface modification to obtain the hydrophilic surface, and the contact angle of the hydrophilic surface is ≥30°.

17. The method according to any one of claims 14 to 16, wherein The surface modification treatment is corona treatment, plasma treatment, chemical treatment, surface grafting treatment or photochemical modification treatment.

18. The method according to any one of claims 14 to 17, wherein The surface modification treatment is corona treatment.

19. A method for preparing the digital microfluidic chip substrate according to any one of claims 11 to 13, wherein: The method comprises: (1) applying the adhesive on the surface of the circuit substrate; (2) Laying the hydrophilic surface of the film on the surface of the adhesive.

20. The method of claim 19, wherein: The method further comprises, in step (2), coating the hydrophobic surface of the film with a protective film.

21. The method according to claim 19 or 20, wherein The method further comprises: (3) processing the thin film on the surface of the circuit substrate in step (2) to obtain a desired shape; (4) removing the protective film to obtain the digital microfluidic chip substrate.

22. Use of the thin film according to any one of claims 1 to 10 to replace a dielectric layer and a hydrophobic layer in the preparation of a digital microfluidic chip.

23. A digital microfluidic chip, comprising the thin film according to any one of claims 1 to 10 or the digital microfluidic chip substrate according to any one of claims 11 to 13. 24 . A digital microfluidic system, comprising the thin film according to claim 1 , the digital microfluidic chip substrate according to claim 1 , or the digital microfluidic chip according to claim 23 .

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