Magnetic responsive membrane with functions of droplet splitting and transporting and preparation and control method thereof

Abstract

The application discloses a kind of magnetic response film with droplet splitting and transport function and its preparation and control method, it is related to droplet control technical field, platinum silica gel polymer precursor liquid, curing agent, softener and magnetic particle are mixed, and the mixture is stirred, form uniform suspension, the uniform suspension is degassed, obtain the suspension after degassing, the suspension after degassing is formed film and solidified, obtain crosslinked film, crosslinked film is soaked in lubricant 30 minutes, after taking out, obtain the magnetic response film with droplet splitting and transport function under the action of external magnetic field, the application can be prepared and obtained a kind of magnetic response film with droplet splitting and transport function under the action of external magnetic field, so as to simultaneously realize droplet splitting function and droplet transport function, i.e. realize the reprogrammable configuration of surface microstructure to realize multifunctional droplet driving.

Description

Technical Field

[0001] This application relates to the field of droplet manipulation technology, and in particular to a magnetically responsive membrane that combines droplet splitting and transport functions, as well as its preparation and control methods. Background Technology

[0002] In recent years, the flexible manipulation of droplets has become increasingly important in scientific research and technological applications, particularly in droplet splitting and transport during aseptic handling and biochemical reagent analysis. For example, droplet splitting is crucial in the sampling and analysis of biochemical reagents, and directional droplet transport enables targeted medical therapy and chip heat dissipation. These applications largely rely on specifically designed surface micro / nanostructures or patterns to achieve different droplet actuations.

[0003] Currently, a common approach is to design anisotropic or gradient micro / nanostructures and wetting patterns to generate unbalanced capillary forces acting on the triple-phase contact line (TPCL) of droplets. For example, some researchers have achieved directional droplet transport by fabricating wedge-shaped surfaces with hierarchical microstructures. However, these specific surface morphologies limit the programmable manipulation of droplets on a single surface; for example, the path or direction of droplet transport is restricted.

[0004] To achieve programmable droplet manipulation, programmable surface micro / nanostructures have been developed by fabricating smart surfaces that can respond to external stimuli (such as light, heat, electricity, chemicals, machinery, and magnetic fields). Magnetic fields, due to their instantaneous response, lack of constraint, and ease of control, are frequently used to stimulate surface morphology. For example, some researchers have fabricated magnetic micropillar arrays, achieving tunable droplet transport by rotating an external magnetic field; others have achieved droplet transport along arbitrary paths by deforming magnetic substrates with magnetic fields; still others have proposed a smart composite interface composed of nanoarrays and filled with magnetofluid, inducing a wetting gradient through a gradient magnetic field to achieve reversible droplet motion.

[0005] Despite significant progress in the design and fabrication of programmable surface micro / nanostructures, current techniques can only achieve simple mechanical deformations of these structures, such as rotational motion, bending, or torsional deformation. Once fabricated, the driving configuration of the surface morphology is limited, thus existing research has largely focused on droplet manipulation using a single strategy. This prevents further pattern reconfiguration and the realization of multifunctional droplet actuation on a single surface.

[0006] Therefore, how to achieve reprogrammable configuration of surface microstructures to realize multifunctional droplet actuation remains an urgent problem to be solved. Summary of the Invention

[0007] The purpose of this application is to provide a magnetically responsive film with both droplet splitting and transport functions, as well as its preparation and control method, which can simultaneously realize droplet splitting and droplet transport functions, that is, to realize the reprogrammable configuration of the surface microstructure to achieve multifunctional droplet actuation.

[0008] To achieve the above objectives, this application provides the following solution:

[0009] In a first aspect, this application provides a method for preparing a magnetically responsive film with both droplet splitting and transport functions, the method comprising:

[0010] The platinum-silicone polymer precursor, curing agent, softener and magnetic particles are mixed and stirred to form a uniform suspension. The uniform suspension is then degassed to obtain a degassed suspension.

[0011] The degassed suspension is then subjected to film formation and solidification to obtain a cross-linked membrane.

[0012] The cross-linked membrane was immersed in a lubricant for 30 minutes and then removed to obtain a magnetically responsive membrane that can perform both droplet splitting and transport functions under the action of an external magnetic field.

[0013] Secondly, this application provides a magnetically responsive membrane with both droplet splitting and transport functions, which is prepared using the above-mentioned method for preparing a magnetically responsive membrane with both droplet splitting and transport functions. The magnetically responsive membrane with both droplet splitting and transport functions comprises: a platinum-silicone polymer matrix, a softener, and magnetic particles. The surface of the platinum-silicone polymer matrix is ​​coated with a lubricant, and the softener and magnetic particles are dispersed in the platinum-silicone polymer matrix.

[0014] Thirdly, this application provides a control method for a magnetically responsive membrane that combines droplet splitting and transport functions, used to control the aforementioned magnetically responsive membrane that combines droplet splitting and transport functions. The control method for the magnetically responsive membrane that combines droplet splitting and transport functions includes:

[0015] Droplet splitting control:

[0016] A first magnetic component is placed below the magnetic response film. The magnetic field strength of the first magnetic component is between 0.25T and 0.35T. The first magnetic field causes the portion of the magnetic response film that is less than a first preset distance from the centerline of the first magnetic component to be in a second state, and the portion of the magnetic response film that is greater than a second preset distance from the centerline of the first magnetic component to be in an initial state. The remaining portion of the magnetic response film forms a wettability gradient region. The roughness of the second state is greater than that of the initial state, and the contact angle of the second state is greater than that of the initial state. The first magnetic component is a permanent magnet or an electromagnet.

[0017] The first magnetic component is moved to cause the droplet located on the upper surface of the magnetic response film to split, thereby achieving droplet splitting;

[0018] Droplet transport control:

[0019] A second magnetic component is placed below the magnetic response film. The magnetic field strength of the second magnetic component is between 0.35T and 0.6T. The second magnetic field causes the portion of the magnetic response film that is less than a third preset distance from the center line of the second magnetic component to be in a second state, and the portion that is more than a fourth preset distance from the center line of the second magnetic component to be in an initial state. The remaining portion of the magnetic response film forms a wettability gradient region. The roughness of the second state is greater than that of the initial state, and the contact angle of the second state is smaller than that of the initial state. The second magnetic component is a permanent magnet or an electromagnet.

[0020] The second magnetic component is moved so that the droplet located on the surface of the magnetic response membrane in the second state moves with the second magnetic component, thereby realizing droplet transport.

[0021] According to the specific embodiments provided in this application, the following technical effects are disclosed:

[0022] This application provides a magnetically responsive membrane with both droplet splitting and transport functions, and its preparation and control method. A platinum-silicone polymer precursor, a curing agent, a softener, and magnetic particles are mixed and stirred to form a uniform suspension. The uniform suspension is then degassed to obtain a degassed suspension. This degassed suspension is then used to form and solidify a cross-linked membrane. The cross-linked membrane is immersed in a lubricant for 30 minutes. After removal, a magnetically responsive membrane capable of both droplet splitting and transport functions under an external magnetic field is obtained. This application can prepare a magnetically responsive membrane capable of both droplet splitting and transport functions under an external magnetic field, thereby simultaneously achieving droplet splitting and droplet transport functions, i.e., realizing reprogrammable configuration of the surface microstructure to achieve multifunctional droplet actuation. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic flowchart illustrating a method for preparing a magnetically responsive membrane with both droplet splitting and transport functions, as provided in Embodiment 1 of this application.

[0025] Figure 2 This is a schematic diagram of the wettability gradient induction process provided in Embodiment 3 of this application.

[0026] Figure 3 This is a schematic diagram illustrating the changes in surface roughness and surface wettability provided in Embodiment 3 of this application; wherein, Figure 3 (a) in the figure represents a three-dimensional confocal microscope image and roughness. Figure 3 (b) shows the change in surface roughness under different conditions as the magnetic field strength changes; Figure 3 (c) in the figure represents the change in surface wettability under different conditions as the magnetic field strength changes.

[0027] Figure 4 This is a three-dimensional confocal microscope image and a schematic diagram of the roughness of the magnetic response film surface in the second state under different magnetic field intensities, as provided in Embodiment 3 of this application; wherein, Figure 4 In the image (a), the three-dimensional confocal microscope image and roughness are at 0.1T. Figure 4 (b) in the figure shows a three-dimensional confocal microscope image and roughness at 0.2T. Figure 4 In the figure, (c) represents the three-dimensional confocal microscope image and roughness at 0.3T; Figure 4 In the figure, (d) represents the three-dimensional confocal microscope image and roughness at 0.4T; Figure 4 In the figure, (e) represents the three-dimensional confocal microscope image and roughness at 0.5T. Figure 4 In the figure, (f) represents the three-dimensional confocal microscope image and roughness at 0.6T.

[0028] Figure 5 This is a schematic diagram illustrating the relationship between contact angle and droplet volume provided in Embodiment 3 of this application.

[0029] Figure 6 This is a schematic diagram of the droplet splitting behavior, experimental snapshot, and theoretical model provided in Embodiment 3 of this application; wherein, Figure 6 (a1)-(a4) in the figure represent the droplet splitting behavior; Figure 6 (b1)-(b7) in the figure are experimental snapshots of the splitting behavior of a 10 μL droplet; Figure 6 (c1) in the figure represents the theoretical model of the splitting behavior of a 10 μL droplet; Figure 6 (c2) in the figure represents the theoretical model of the splitting behavior of a 20 μL droplet; Figure 6 (d1)-(d7) in the figure are experimental snapshots of the splitting behavior of 20 μL droplets.

[0030] Figure 7 This is a schematic diagram of droplet splitting behavior and experimental snapshots under Mode 1 provided in Embodiment 3 of this application; wherein, Figure 7 (a1) in the figure represents the effect of the permanent magnet's stopping position on the new droplet volume; Figure 7(b1)-(b8) are snapshots of the experiment where a 10 μl droplet was split into two droplets of significantly different volumes due to the different stopping positions of the permanent magnet. Figure 7 (c1)-(c8) are experimental snapshots showing how a 10 μl droplet was split into two droplets of significantly different volumes due to the different stopping positions of the permanent magnet.

[0031] Figure 8 This is a schematic diagram illustrating the droplet splitting behavior and contact angle changes in Mode 2 and Mode 3 provided in Embodiment 3 of this application; wherein, Figure 8 (a) in the diagram represents the droplet splitting behavior under mode 2; Figure 8 (b) in the diagram represents the droplet splitting behavior under mode 3; Figure 8 (c) in the figure represents the contact angle changes under mode 1 and mode 2; Figure 8 (d) in the figure represents the contact angle change under mode 3.

[0032] Figure 9 This is a schematic diagram of experimental snapshots of droplet splitting behavior in modes 2 and 3 provided in Embodiment 3 of this application; wherein, Figure 9 (a1)-(a8) in the figure are experimental snapshots of the splitting behavior of a 10 μL droplet under mode 2; Figure 9 (b1)-(b16) in the figure are experimental snapshots of the splitting behavior of a 30 μL droplet under mode 2; Figure 9 (c1)-(c8) in the figure are experimental snapshots of the splitting behavior of a 30 μL droplet under mode 3.

[0033] Figure 10 This is a schematic diagram of the stealth air knife splitting droplets provided in Embodiment 3 of this application; wherein, Figure 10 (a1)-(a14) in the figure represent the continuous splitting behavior of a 10 μL droplet; Figure 10 (b1)-(b12) represent the droplet splitting and polymerization behavior; Figure 10 (c1)-(c12) represent the inhibitory and promoting behaviors of droplet splitting.

[0034] Figure 11 This is a schematic diagram of the droplet transport behavior and experimental snapshot provided in Embodiment 3 of this application; wherein, Figure 11 (a1)-(a3) in the figure represent the droplet transport behavior; Figure 11 (b1)-(b12) in the figure are experimental snapshots of the droplet transport behavior.

[0035] Figure 12 The influence of magnetic field velocity and droplet volume on droplet transport behavior is provided in Embodiment 3 of this application. Detailed Implementation

[0036] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] Example 1

[0038] like Figure 1 As shown, this embodiment provides a method for preparing a magnetically responsive film with both droplet splitting and transport functions. The method for preparing the magnetically responsive film with both droplet splitting and transport functions includes:

[0039] S1: Mix the platinum silicone polymer precursor liquid, curing agent, softener and magnetic particles, and stir the mixture to form a uniform suspension. Degas the uniform suspension to obtain a degassed suspension.

[0040] S2: The degassed suspension is subjected to film formation and solidification to obtain a cross-linked membrane.

[0041] S3: Immerse the cross-linked membrane in a lubricant for 30 minutes, and then remove it to obtain a magnetically responsive membrane that can perform both droplet splitting and transport functions under the action of an external magnetic field.

[0042] In this embodiment, the mass ratio of platinum silicone polymer precursor liquid to curing agent can be 1:1, the mass percentage of softener can be 40wt%, that is, the mass of softener is 40% of the total mass of platinum silicone polymer precursor liquid, curing agent and softener, and the mass percentage of magnetic particles can be 100wt%, that is, the mass of magnetic particles is 100% of the total mass of platinum silicone polymer precursor liquid, curing agent and softener and magnetic particles.

[0043] At this point, S1 may include: mixing platinum silicone polymer precursor liquid and curing agent in a mass ratio of 1:1, adding 40wt% softener, and then adding 100wt% magnetic particles to obtain a mixture, vigorously stirring the mixture to form a uniform suspension, and degassing the uniform suspension to obtain a degassed suspension.

[0044] The stirring method can be any existing stirring method, such as mechanical stirring, and the degassing treatment method can be any existing degassing treatment method. This embodiment does not impose any restrictions on this.

[0045] In this embodiment, the curing temperature can be 70°C and the curing time can be 10 minutes.

[0046] At this point, S2 may include: pouring the degassed suspension onto a hard substrate, preparing a thin-layer mixture with a thickness of 500 μm using a coating technique, and curing the thin-layer mixture at 70°C for 10 min to obtain a crosslinked film.

[0047] In this embodiment, the lubricant may be dimethyl silicone oil.

[0048] At this point, S3 may include: immersing the crosslinked membrane in dimethyl silicone oil for 30 minutes, and then removing it to obtain a magnetically responsive membrane that can perform both droplet splitting and transport functions under the action of an external magnetic field.

[0049] The magnetically responsive membrane prepared in this embodiment, which combines droplet splitting and transport functions, has a sliding magnetically responsive surface, that is, a reprogrammable microstructure surface, which can simultaneously realize droplet splitting and droplet transport functions.

[0050] The platinum-silicone polymer is Smooth-on Ecoflex 00-30, the magnetic particles can be carbonyl iron particles (CIPs) with a diameter of 1-3 μm, and the dimethyl silicone oil can be PMX-200 with a pressure of approximately 10 mPa·s.

[0051] Example 2

[0052] This embodiment provides a magnetically responsive membrane with both droplet splitting and transport functions. It is prepared using the method for preparing a magnetically responsive membrane with both droplet splitting and transport functions described in Example 1. The magnetically responsive membrane with both droplet splitting and transport functions includes: a platinum-silicone polymer matrix, a softener, and magnetic particles. The platinum-silicone polymer matrix is ​​obtained by curing a platinum-silicone precursor liquid with a curing agent. The surface of the platinum-silicone polymer matrix is ​​coated with a lubricant, and the softener and magnetic particles are dispersed in the platinum-silicone polymer matrix.

[0053] In this embodiment, the thickness of the magnetically responsive film that combines droplet splitting and transport functions can be 500 μm.

[0054] Example 3:

[0055] This embodiment first verifies the performance of the magnetically responsive film of Example 2 prepared using the preparation method of Example 1 through experiments, as follows:

[0056] (1) Surface morphology and wetting properties

[0057] Figure 2 This is a schematic diagram of the wettability gradient induced process, when the magnetic response membrane (i.e. Figure 2When the thin film (in the image) is placed in an external magnetic field, generated by two stacked permanent magnets measuring 15mm*10mm*4mm, the magnetic moments on the magnetic particles immediately take effect. Under the influence of these magnetic moments, localized areas of the platinum-silicone polymer matrix are stretched upwards, forming a rough microstructure. This portion of the magnetically responsive film is in its second state, while areas far from the magnetic field remain in their initial state. As the distance from the magnetic field increases, the magnetic field strength gradually decreases, leading to a continuous change in surface roughness and wettability. Therefore, a wettability gradient (i.e., ...) is formed between the initial and second states. Figure 2 (The wetting gradient in the middle). When the magnetic field is removed from the second state, the second state transitions to the third state.

[0058] Figure 3 (a) shows a three-dimensional confocal microscopy image of the magnetically responsive film surface and its roughness Ra, which is 16.54 μm in the initial state. The three-dimensional confocal microscopy image was obtained by a 3D laser scanning confocal microscope to observe the surface morphology and configuration. Figure 3 Figure (b) shows the roughness variation in three states under different magnetic field intensities. Figure 4 Three-dimensional confocal microscopy images and roughness of the magnetically responsive film surface in its second state under different magnetic field strengths are shown. Since the roughness in the initial state is independent of the magnetic field strength, it remains at 16.54 μm regardless of the magnetic field change. In the second state, as the magnetic field strength increases from 0.1 T to 0.6 T, the roughness rapidly increases from 23.43 μm to 71.09 μm. After the magnetic field is removed, the second state transitions to the third state, and the roughness in the third state almost recovers to the roughness of the initial state, verifying the excellent reprogrammable performance of the functional surface of the magnetically responsive film.

[0059] Since droplet manipulation on a surface primarily depends on its wetting properties, Figure 3 Figure (c) illustrates the variation of surface wettability with magnetic field strength under different states. It can be observed that in the initial state, since surface wettability is independent of the magnetic field, the contact angle and sliding angle remain constant. In the second state, with increasing surface roughness at lower magnetic field strengths, the contact angle increases while the sliding angle decreases. When the microstructure surface of the magnetically responsive film is sufficiently increased, the droplet wets the gaps between the microstructure surfaces. When the droplet wets the gaps between the microstructure surfaces, the three-phase contact line length increases and the resistance strengthens. Therefore, with increasing magnetic field strength, the sliding angle also increases.

[0060] In this embodiment, the contact angle and sliding angle of the magnetically responsive membrane were measured using the OCA25 contact angle system, with droplet volumes of 5 μL and 15 μL, respectively.

[0061] The relationship between the contact angle and the volume of the droplet outside the microstructure surface is shown in equation (1):

[0062]

[0063] In equation (1), θ, R and V represent the contact angle, droplet radius and droplet volume outside the microstructure surface, respectively.

[0064] Equation (1) shows that the contact angle changes monotonically with the droplet volume. When the droplet wets the gaps in the microstructure surface, the droplet volume outside the microstructure surface decreases, leading to a decreasing trend in the contact angle. This indicates that the surface wetting properties in the second state are reprogrammable by adjusting the applied magnetic field.

[0065] The derivation of equation (1) is as follows:

[0066] Figure 5 A schematic diagram illustrating the configuration and geometry of droplet deposition on a thin film surface is shown, from... Figure 5 We can obtain:

[0067]

[0068] In equation (2), θ, H, and R represent the apparent contact angle, height, and radius of the droplet, respectively.

[0069] The volume V of the droplet can be written as:

[0070]

[0071] Combining equations (2) and (3), we can obtain:

[0072]

[0073] Assuming θ is a function of volume V, and differentiating both sides of equation (4) with respect to V, we get:

[0074]

[0075] because:

[0076]

[0077] therefore:

[0078]

[0079] This indicates that the contact angle θ changes monotonically with the droplet volume V.

[0080] (2) Droplet splitting behavior and theoretical analysis

[0081] After inducing a wettability gradient, the gradient shifts accordingly with the movement of the magnetic field beneath the film. The local region above the magnetic component transitions to a second state, while the region farther from the magnetic component reverts to its initial state, all within milliseconds. When the droplet is located within the wettability gradient region, an unbalanced capillary force F is generated acting on the droplet's three-phase contact line. driving It can be simplified to:

[0082] F driving =2Rγ(cosθ) h -cosθ l (8)

[0083] In equation (8), R represents the radius of the droplet; γ represents the liquid-gas surface tension; θ h and θ l ... Figure 3 As can be seen from (c), a larger driving force can be obtained when the magnetic field strength is 0.3T or 0.6T.

[0084] When a magnetic field of 0.3T is applied under the thin film, the contact angle in the second state is 112°, and the contact angle in the initial state is 103.7°. Figure 3 As shown in (c) above. A 10 μL droplet is deposited on a local surface in the second state and along... Figure 6 The dashed arrows in (a1), (b1), and (b2) indicate the movement of the magnetic field, causing the wettability gradient region to move accordingly. When the wettability gradient region reaches the droplet's position, a driving force is immediately applied to the droplet, transporting it from the second state to the initial state. The droplet configuration transported on the surface of the wettability gradient region will exhibit an elongated elliptical shape. Furthermore, Figure 3 (c) shows that the sliding angle in the second state is 21°, as shown in Figure (c). Figure 6 As shown in (a2), the three-phase contact line of the droplet is fixed, i.e., pinned. Therefore, under the combined action of the driving force and the fixing effect, the elongated droplet configuration is further stretched and evolves into a dumbbell shape, as... Figure 6 As shown in (a3), (b3), (b4), and (b5).

[0085] The theoretical model of a dumbbell-shaped droplet can be found in... Figure 6The description is roughly as shown in (c1). Clearly, if the Laplace pressure in the neck region (plane 1) is greater than the pressure in the expansion region (plane 2), the droplet will flow from plane 1 to plane 2, thus splitting the droplet into a dumbbell shape. The critical condition for droplet splitting is expressed as:

[0086]

[0087]

[0088] In the above formula, r s and R s Let l represent the positive radii of curvature of plane 1 and plane 2, respectively; AB d represents the distance between plane 1 and plane 2; d0 represents the half-width of the elongated droplet; a n and b n These represent the magnitudes of the driving force and pinning effect disturbances, respectively.

[0089] Obviously, l AB The larger or r s and R s The smaller the droplet, the easier it is to separate it. For example... Figure 6 As shown in (b4) and (b5), l AB Much greater than r s and R s Therefore, the diameter of plane 1 gradually decreases, and the diameter of plane 2 gradually increases, until the droplet is pulled apart, as shown. Figure 6 As shown in (a4) and (b6) in the diagram. Because the deformation energy of the original droplet is converted into the kinetic energy of the newly formed droplet through the splitting behavior, the newly formed droplet... Figure 6 As shown in (b7), the droplets move in the opposite direction. Due to surface resistance, the moving droplets will stop.

[0090] However, from Figure 6 (b7) also shows that a tiny droplet is formed during the splitting process. In fact, when the three-phase contact line configuration of the droplet changes from an elongated state to a dumbbell shape, as... Figure 6 As shown in (c1), a short column of liquid forms between plane 1 and plane 3, which is the triggering factor for the micro-droplets. Because plane 1 and plane 3 have already split before all the droplets flow from the neck region to the expansion region, the residual droplets exist in the form of micro-droplets.

[0091] Further investigation in this embodiment revealed that the size of the microdroplet depends on the total volume of the droplet. When the droplet volume is 20 μL, as... Figure 6 As shown in (d1)-(d7). Figure 6 (d3) and (d4) in the data show that, with Figure 6Compared to the three-phase contact line configurations in (b1)-(b7), the three-phase contact line configuration is now elongated and ultimately forms three droplets because there is an excess of residual droplets in the short column between plane 1 and plane 3 sufficient to form an isolated droplet, such as Figure 6 As shown in (c2) in the diagram.

[0092] The derivation of the critical condition for droplet splitting is as follows:

[0093] like Figure 6 As shown in (c1), a schematic diagram of a dumbbell-shaped droplet is provided, establishing a Cartesian coordinate system xf. Clearly, due to the positive and negative curvature of the surface, a Laplace pressure is induced, which can be expressed as:

[0094]

[0095] In equation (11), γ represents the surface tension of the droplet; r s r c R s and R c These represent the positive and negative radii of curvature corresponding to plane 1 and plane 2, respectively.

[0096] Any contour can be represented by a Fourier series; therefore, the configuration of the three-phase contact line of a dumbbell-shaped droplet can be expressed as:

[0097]

[0098] In equation (12), d0 and l AB These represent the half-width of the elongated droplet and the distance between plane 1 and plane 2, respectively; a n and b n Let represent the amplitudes of the driving force and the pinning effect disturbance, respectively. The extremum condition of equation (12) can be written as:

[0099]

[0100] In equation (13), plane 1 represents plane 1; plane 2 represents plane 2.

[0101] Substituting equation (13) into equation (12), we get:

[0102]

[0103] The first and second derivatives of the function f can be written as:

[0104]

[0105] The formula for curvature ρ is:

[0106]

[0107] Combining equations (11), (15), and (16), the total Laplace pressure of plane 1 and plane 2 can be obtained as follows:

[0108]

[0109] For the droplet to split, the Laplace pressure in the neck region (plane 1) needs to be greater than the Laplace pressure in the expansion region (plane 2), that is:

[0110]

[0111] Combining equations (14), (17), and (18), the critical condition for droplet splitting can be derived as follows:

[0112]

[0113] (3) Multiple droplet splitting strategies

[0114] Besides tiny droplets, the location of the moving magnetic field beneath the thin film was found to significantly influence the main droplet formation and splitting modes. Based on the position of the moving magnetic component, droplet splitting behavior can be categorized into three strategies.

[0115] The first strategy (Mode 1) involves the droplet initially depositing in the second-state region, with the magnetic component eventually settling below the droplet, and its splitting behavior as follows: Figure 6 (b1)-(b7) and Figure 6 As shown in (d1)-(d7). In this case, the two newly formed droplets are almost the same size because the edge of the stopping magnetic component stops at a small distance from the droplet centerline. However, when the edge of the magnetic component stops at a larger distance from the droplet centerline, droplets with significant volume differences are formed, such as... Figure 7 As shown.

[0116] The second strategy (Mode 2) involves the droplet initially depositing in the second-state region, while the magnetic component eventually settles away from the droplet, such as... Figure 8 (a) In Mode 2, the splitting behavior of 10 μL and 30 μL droplets is as follows: Figure 9 As shown in (a1)-(a8) and (b1)-(b16). Because the stopped magnetic component is far from the droplet, and the droplet is in the third state region, the impact force on the extending droplet is very small, resulting in... Figure 6 The liquid column between plane 1 and plane 3 in (c1) is almost negligible. Figure 6 (b1)-(b7), (d1)-(d7) and Figure 9The splitting times marked in (a1)-(a8) and (b1)-(b16) show that the elliptical and dumbbell-shaped three-phase contact lines in Mode 2 have shorter durations than in Mode 1, even though... Figure 9 The droplet volume ratio in (b1)-(b8) Figure 6 The (d1)-(d7) values ​​are much larger. Therefore, when the second strategy is used, only two complete droplets are formed, and no tiny droplets are formed.

[0117] Due to the kinetic energy of the newly formed droplet, the droplet rapidly moves towards the stationary magnetic component, and then, under the influence of the wettability gradient, extends and breaks up again, such as... Figure 9 As shown in (b9)-(b16).

[0118] By gradually moving the magnetic component onto the droplet initially deposited in the first-state region, the droplet's splitting behavior can also be achieved, such as... Figure 8 As shown in (b), this is defined as the third strategy (mode 3). In modes 1 and 2, the left portion of the three-phase contact line is first affected by tension due to the shift in the wettability gradient, as the contact angle changes from a larger value to a smaller value, such as... Figure 8 As shown in (c), the solid line represents the original contact angle, and the dashed line represents the changed contact angle. In Mode 3, the left side of the three-phase contact line is first affected by the thrust because the contact angle changes from a smaller value to a larger value, as... Figure 8 As shown in (d) in the diagram. Therefore, the droplet's spreading behavior is restricted and initially resists external disturbances until the wettability gradient region completely covers the droplet. Consequently, the formation of the liquid column between planes 1 and 3 is suppressed, and the droplet splits into two new droplets, regardless of their volume, as shown in (d). Figure 9 As shown in (c1)-(c8).

[0119] Based on these three strategies, a movable wettability gradient on a functional surface can act as a stealthy air knife to split droplets in multiple ways, such as... Figure 10 As shown. Combining modes 2 and 3, continuous droplet splitting behavior of a 10 μL droplet was achieved by controlling the stealth air knife, as... Figure 10 As shown in (a1)-(a14), the merging phenomenon between the first formed droplet 1 and the subsequent formed droplet 2 was observed during this period.

[0120] Furthermore, droplets can also rapidly break apart when they spontaneously impact or move away from the air knife. When droplets are deposited in the initial region and the film surface is tilted, the droplets impact the air knife and rapidly break apart, as shown in the example. Figure 10 As shown in (b1)-(b6). At this point, placing a horizontal but tilted magnetic component on the film surface will reduce the magnetic field strength on the film, leading to a newly formed wettability gradient and a reduced contact angle hysteresis, as... Figure 3As shown in (c) above. This movable wettability gradient can drive the movement of newly formed droplets and their aggregation with another droplet, as... Figure 10 As shown in (b7)-(b12).

[0121] As can be seen from the above phenomena, the droplet's elongation behavior is crucial for droplet splitting or satisfying equation (9). However, if the droplet's elongation configuration can be overcome or enhanced by external factors, the droplet splitting behavior will be inhibited or promoted. Figure 10 As shown in (c1)-(c12), when the film surface is placed on a 10° inclined plane and a large droplet 1 with a volume of 30 μL is directly deposited in the wettability gradient region, the spreading behavior is significantly suppressed due to the greater gravity, as shown in (c1)-(c12). Figure 10 As shown in (c1)-(c2). After 2.53 seconds of driving force resisting gravity, the droplet rapidly crosses the wettability gradient region and merges with pre-placed droplets 2 and 3 within 0.2 seconds, as shown in (c1)-(c2). Figure 10 As shown in (c3)-(c7). Since the extended configuration of the droplets is enhanced by the increase in volume, the droplet splitting rate is greatly accelerated. At this time, the pre-placed droplet 4 merges with the newly formed droplet, as shown... Figure 10 As shown in (c8)-(c12).

[0122] While functional surfaces have been used for droplet splitting, fixed patterns / positions on the surface are always required for droplet activation or complex fabrication processes. In contrast, due to the mobility of the wettability gradient, the droplet splitting behavior in this embodiment can be achieved at any location on the surface and can be implemented in multiple modes. Furthermore, the fabrication process is simple and can be mass-produced. This droplet splitting technology can be applied in the fields of biochemical reagent sampling and chemical reactions in extremely sterile environments.

[0123] (4) The reciprocating transport behavior of droplets

[0124] like Figure 3 As shown in (c), the surface wettability in the second state can be reprogrammed by adjusting the magnetic field strength. After applying a magnetic field of 0.6T under the film, the contact angle in the second state is 87.5°, which is much smaller than the contact angle in the initial state (103.7°), and the sliding angle is 28°. Therefore, the wettability of the second state region is higher, while the wettability of the initial state region is lower, which is the opposite of the droplet splitting situation shown in (2) and (3).

[0125] Based on this movable wettability gradient, the reciprocating transport of droplets can be well achieved, such as... Figure 11 As shown. Droplets are deposited in the second-state region, and the wettability gradient is moved, as... Figure 11As shown in (a1), (b1), and (b2), a driving force is rapidly generated acting on the three-phase contact line, propelling the droplet from the region of high wettability to the region of low wettability. Due to the large contact angle hysteresis in the second-state region, the droplet is fixed, as... Figure 11 As shown in (a2), with the continuous movement of the wettability gradient, the droplet is transported accordingly and always remains at the edge of the second state region, as... Figure 11 As shown in (a2), (a3), (b3)-(b6). Figure 11 Figures (b6) and (b7) show that the moving droplet stops before the wettability gradient reaches its position. Similarly, the droplet is transported along a movable wettability gradient, such as... Figure 11 As shown in (b8)-(b12).

[0126] This embodiment further investigates the effects of magnetic field velocity and droplet volume on transport behavior, such as Figure 12 As shown, it was found that the smaller the droplet volume, the lower the magnetic field velocity, and the easier the droplet transport. When the droplet volume is large enough, droplet transport cannot be achieved regardless of the change in magnetic field velocity, because the long three-phase contact line of a large droplet increases the resistance.

[0127] For a droplet of fixed volume, a new equilibrium state is reached when the wettability gradient reaches the droplet's location, which takes time due to the droplet's viscosity. If the magnetic field moves too quickly, the wettability gradient will pass through the droplet before the new equilibrium state is established. Therefore, in this case, droplet transport behavior is also impossible.

[0128] Various functional surfaces have been designed and fabricated to transport droplets. Droplet motion is typically caused by gravity, shape gradients, or pre-designed paths, making reciprocating transport difficult to achieve on a horizontal surface. However, the droplet transport technology proposed in this embodiment is not limited by pre-designed trajectories and directions. Furthermore, reciprocating transport of droplets can be achieved remarkably well. This technology holds significant promise for applications in targeted therapy in clinical medicine and heat transfer in laboratory chips.

[0129] Droplet manipulation has important applications in various fields, particularly droplet splitting and transport in aseptic operations and biochemical reagent analysis. However, existing functional surfaces are limited to pre-designed microstructures or fixed patterns for droplet splitting or transport, and realizing programmable surface microstructures to freely control droplet splitting and transport remains a significant challenge. This embodiment proposes a flexible technique for achieving multimodal droplet splitting and reciprocating transport on a single surface. A simple preparation method is developed by premixing magnetic particles and a softener into a polymer solvent and further impregnating it with a lubricant. An external magnetic field generates a movable wettability gradient on the droplet surface, acting as an invisible air knife to achieve multimodal droplet splitting. The mechanism and critical conditions of droplet splitting are theoretically analyzed and revealed. Furthermore, by adjusting the magnetic field strength, the microstructure configuration and surface wettability can be reprogrammed, transforming droplet splitting behavior into reciprocating transport behavior, and the factors influencing this behavior are analyzed in detail. The reprogrammable operation of droplets on a single surface reported in this embodiment provides a general model for droplet actuation in microfluidics and bioanalytical devices.

[0130] Based on the above experimental results, this embodiment provides a control method for a magnetically responsive membrane with both droplet splitting and transport functions, used to control the magnetically responsive membrane with both droplet splitting and transport functions described in Embodiment 2. The control method for the magnetically responsive membrane with both droplet splitting and transport functions includes:

[0131] (1) Droplet splitting control:

[0132] A first magnetic component is placed beneath the magnetic response film. The magnetic field strength of the first magnetic component is between 0.25T and 0.35T. The first magnetic field causes a portion of the magnetic response film located at a distance less than a first preset distance from the centerline of the first magnetic component to be in a second state, while a portion located at a distance greater than a second preset distance from the centerline of the first magnetic component is in an initial state. The remaining portion of the magnetic response film forms a wettability gradient region. The roughness of the second state is greater than that of the initial state, and the contact angle of the second state is greater than that of the initial state. The first magnetic component is a permanent magnet or an electromagnet.

[0133] The first magnetic component is moved to cause the droplet located on the upper surface of the magnetic response membrane to split, thus achieving droplet splitting.

[0134] (2) Droplet transport control:

[0135] A second magnetic component is placed below the magnetic response film. The magnetic field strength of the second magnetic component is between 0.35T and 0.6T. The second magnetic field causes a portion of the magnetic response film located at a distance less than a third preset distance from the centerline of the second magnetic component to be in a second state, while a portion located at a distance greater than a fourth preset distance from the centerline of the second magnetic component is in an initial state. The remaining portion of the magnetic response film forms a wettability gradient region. The roughness of the second state is greater than that of the initial state, and the contact angle of the second state is smaller than that of the initial state. The second magnetic component is a permanent magnet or an electromagnet.

[0136] The second magnetic component is moved so that the droplet located on the surface of the magnetic response membrane in the second state moves with the second magnetic component, thereby realizing droplet transport.

[0137] Specifically, moving the first magnetic component to cause the droplet located on the upper surface of the magnetic response film to split includes:

[0138] If the droplet is located on the upper surface of the magnetic response film in the second state, the first magnetic component is moved until the droplet is located on the upper surface of the wettability gradient region for the first time. Then the movement of the first magnetic component is stopped, causing the droplet to split into three new droplets.

[0139] If the droplet is located on the upper surface of the magnetic response film in the second state, the first magnetic component is moved until the droplet is located on the upper surface of the wettability gradient region for the first time and then on the upper surface of the magnetic response film in the initial state. At this point, the movement of the first magnetic component is stopped, causing the droplet to split into two new droplets.

[0140] If the droplet is located on the upper surface of the magnetic response film in its initial state, the first magnetic component is moved until the droplet is located on the upper surface of the wettability gradient region for the first time. Then, the movement of the first magnetic component is stopped, causing the droplet to split into two new droplets.

[0141] Specifically, stopping the movement of the first magnetic component to split the droplet into three new droplets includes: if, when the movement of the first magnetic component stops, the distance between the near edge of the first magnetic component and the center line of the droplet is less than a fifth preset distance, then the volume difference between the two outer droplets of the three new droplets is less than a first threshold; if, when the movement of the first magnetic component stops, the distance between the near edge of the first magnetic component and the center line of the droplet is greater than a sixth preset distance, then the volume difference between the two outer droplets of the three new droplets is greater than a second threshold; the near edge is the edge of the first magnetic component that is closer to the droplet.

[0142] Preferably, the magnetic field strength of the first magnetic field is 0.3T and the magnetic field strength of the second magnetic field is 0.6T.

[0143] To develop a reprogrammable functional surface for multifunctional droplet manipulation, this embodiment employs a simple method to fabricate a magnetically responsive film. A movable wettability gradient is induced by an external magnetic field, and its surface morphology and wettability are investigated in detail. Due to its reversible orientation and variable microstructure shape / pattern configuration, this wettability gradient is reprogrammable. Utilizing unbalanced capillary forces and the reprogrammable wettability of different regions, droplet splitting and reciprocating transport behaviors were successfully achieved on a single surface by adjusting the magnetic field strength.

[0144] In this embodiment, the scale bar for all experimental snapshot markers is 5mm.

[0145] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0146] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for controlling a magnetically responsive membrane that combines droplet splitting and transport functions, used to control the magnetically responsive membrane, wherein the method for preparing the magnetically responsive membrane includes: A platinum-silicone polymer precursor, curing agent, softener, and magnetic particles are mixed and stirred to form a uniform suspension. The uniform suspension is then degassed to obtain a degassed suspension. The degassed suspension is then used to form and cure a cross-linked film. The cross-linked film is immersed in a lubricant for 30 minutes and then removed to obtain a magnetically responsive film that can perform both droplet splitting and transport functions under the action of an external magnetic field. The mass ratio of the platinum-silicone polymer precursor to the curing agent is 1:1, the softener has a mass percentage of 40 wt%, and the magnetic particles have a mass percentage of 100 wt%. The method for controlling the magnetically responsive film with droplet splitting and transport functions includes: Droplet splitting control: A first magnetic component is placed below the magnetic response film. The magnetic field strength of the first magnetic component is between 0.25T and 0.35T. The first magnetic field causes the portion of the magnetic response film that is less than a first preset distance from the centerline of the first magnetic component to be in a second state, and the portion of the magnetic response film that is greater than a second preset distance from the centerline of the first magnetic component to be in an initial state. The remaining portion of the magnetic response film forms a wettability gradient region. The roughness of the second state is greater than that of the initial state, and the contact angle of the second state is greater than that of the initial state. The first magnetic component is a permanent magnet or an electromagnet. The first magnetic component is moved to cause the droplet located on the upper surface of the magnetic response film to split, thereby achieving droplet splitting; Droplet transport control: A second magnetic component is placed below the magnetic response film. The magnetic field strength of the second magnetic component is between 0.35T and 0.6T. The second magnetic field causes the portion of the magnetic response film that is less than a third preset distance from the center line of the second magnetic component to be in a second state, and the portion that is more than a fourth preset distance from the center line of the second magnetic component to be in an initial state. The remaining portion of the magnetic response film forms a wettability gradient region. The roughness of the second state is greater than that of the initial state, and the contact angle of the second state is smaller than that of the initial state. The second magnetic component is a permanent magnet or an electromagnet. The second magnetic component is moved so that the droplet located on the surface of the magnetic response membrane in the second state moves with the second magnetic component, thereby realizing droplet transport.

2. The control method for a magnetically responsive membrane with both droplet splitting and transport functions according to claim 1, characterized in that, Moving the first magnetic component causes the droplet located on the upper surface of the magnetic response film to split, specifically including: If the droplet is located on the upper surface of the magnetic response film in the second state, the first magnetic component is moved until the droplet is located on the upper surface of the wettability gradient region for the first time, at which point the movement of the first magnetic component is stopped, causing the droplet to split into three new droplets. If the droplet is located on the upper surface of the magnetic response film in the second state, the first magnetic component is moved until the droplet is located on the upper surface of the wettability gradient region for the first time and then on the upper surface of the magnetic response film in the initial state. Then the movement of the first magnetic component is stopped, causing the droplet to split into two new droplets. If the droplet is located on the upper surface of the magnetic response film in its initial state, the first magnetic component is moved until the droplet is located on the upper surface of the wettability gradient region for the first time. Then, the movement of the first magnetic component is stopped, causing the droplet to split into two new droplets.

3. The control method for a magnetically responsive membrane with both droplet splitting and transport functions according to claim 2, characterized in that, Stop moving the first magnetic component to split the droplet into three new droplets. Specifically, if the distance between the near edge of the first magnetic component and the center line of the droplet is less than a fifth preset distance when the first magnetic component is stopped, the volume difference between the two outer droplets in the three new droplets is less than a first threshold. If the distance between the near edge of the first magnetic component and the center line of the droplet is greater than a sixth preset distance when the first magnetic component is stopped, the volume difference between the two outer droplets in the three new droplets is greater than a second threshold. The near edge is the edge of the first magnetic component that is closer to the droplet.

4. The control method for a magnetically responsive membrane with both droplet splitting and transport functions according to claim 1, characterized in that, The magnetic field strength of the first magnetic field is 0.3T; the magnetic field strength of the second magnetic field is 0.6T.

5. The control method for a magnetically responsive membrane with both droplet splitting and transport functions according to claim 1, characterized in that, The curing temperature is 70℃ and the curing time is 10 minutes.

6. The control method for a magnetically responsive membrane with both droplet splitting and transport functions according to claim 1, characterized in that, The magnetic particles are carbonyl iron particles; the lubricant is dimethyl silicone oil.

7. The control method for a magnetically responsive membrane with both droplet splitting and transport functions according to claim 1, characterized in that, The magnetically responsive film comprises: a platinum-silicone polymer matrix, a softener, and magnetic particles. The surface of the platinum-silicone polymer matrix is ​​coated with a lubricant, and the softener and magnetic particles are dispersed in the platinum-silicone polymer matrix.

8. The control method for a magnetically responsive membrane with both droplet splitting and transport functions according to claim 1, characterized in that, The thickness of the magnetically responsive film is 500 μm.

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