Integrated single-fiber droplet manipulator

Abstract

The present invention provides an integrated single-fiber microdroplet manipulator. Its characteristics are as follows: The device consists of a multi-core optical fiber including a cladding and a core. The fiber end is ground to form a frustum-shaped fiber end. There is a liquid-injected smooth porous surface film doped with a photosensitive material on the end face of the frustum-shaped fiber end. This film has an array trench structure filled with a lubricant. When the light wave transmitted through the core is reflected by the frustum-shaped fiber end and converges on the liquid-injected smooth porous surface film on the end face, it is absorbed by the photosensitive material and converted into heat energy, forming a temperature gradient field in the irradiation area. This causes the microdroplets attached to the liquid-injected smooth porous surface film to generate a wetting gradient force under the influence of the temperature gradient field. Under the influence of the force, the posture of the microdroplets will change and generate directional sliding. Finally, by controlling the power of the light injected into the core, the manipulation of the microdroplets can be achieved under the action of different temperature gradient fields. The present invention can be used in the fields of fluid mechanics, biology, medicine, etc.

Description

(1) Technical Field

[0001] The present invention provides an integrated single-fiber droplet manipulator, which can be used in the fields of fluid mechanics, biology, medicine, etc. (2) Background Art

[0002] As a new information functional material, optical fiber has become a new favorite in the fields of biology, chemistry, laser, and sensing in recent years due to its advantages such as long transmission distance, fast transmission speed, low loss, strong anti-interference ability, in-vivo detection, high sensitivity, fast response speed, and strong biocompatibility, which are not possessed by other functional materials. Scientists have realized functions such as optical tweezers, optical manipulation, and optical detection by designing various microstructured antennas and thin films at the fiber end.

[0003] There are various natural superhydrophobic surfaces with micro-nano composite structures in nature. For example, the microstructures on the lotus leaf surface can form a stable gas-liquid interface layer, making water droplets roll off easily and thus having excellent anti-fouling properties; similarly, there is the Namib Desert beetle living in the Namib Desert. Its back has a hard elytra with peaks and valleys like grooves that allow it to collect water from the fog at night; while the Nepenthes, as an ornamental potted plant, has a hydrophilic lubricating film on the colored lip leaf at its top, which makes the insects that land on it slide into the digestive system at the bottom. Inspired by this, scientists have prepared a slippery liquid infused porous surface (SLIPS) that mimics the Nepenthes structure. The SLIPS has unique advantages in anti-fouling, promoting dropwise condensation, anti-frost and anti-icing, oil-water separation, etc., and has been a research hotspot in recent years. For example, the team of scientist Tian used ZnO nanorod arrays infused with magnetic fluid (MF) to control droplets with controllable and rapid response characteristics (Advanced Materials, 2017, 29(45): 1702802). This device achieved continuous driving of underwater oil droplets under the control of directional movement. However, this device is not portable but energy-consuming. Moreover, the inherent fluidity and volatility of the magnetic fluid may reduce the lifespan of the resulting system; the team of scientist Heng prepared a porous conductive film that can achieve electrically driven droplet movement by changing the voltage and explored the influence of lubricant viscosity on the self-healing performance (Journal of Materials Chemistry, A. Materials for energy and sustainability, 2018, 6, 2414 - 2421); the team of scientist Hu prepared a dynamically driven liquid-infused porous elastic film that can control droplet dynamics through voltage (Advanced Functional Materials, 2018, 28, 1802622.). However, the above devices require complex external energy input. For example, when applying voltage to a photo-thermo synergistic response material, additional electrical energy is required, which is not convenient for manipulating biological droplets.

[0004] An integrated single-fiber micro-droplet manipulator designed by us innovatively combines an optical fiber and a slippery liquid infused porous surface, which can avoid most of the mechanical wear suffered by the slippery liquid infused porous surface during use, resulting in the gradual loss of surface wettability and increasing its service life; at the same time, a thermosensitive film with photosensitive dopants is prepared on the multi-core fiber frustum or wedge-shaped fiber tip, and a hydrophobic array is made on the film surface. By changing the different arrangements of the fiber cores and the power and wavelength of the light waves transmitted by each core, the directional movement and the change of the movement state of the micro-droplets can be achieved. (III) Summary of the Invention

[0005] The object of the present invention is to provide an integrated single-fiber microdroplet manipulator.

[0006] The object of the present invention is achieved as follows:

[0007] The present invention provides an integrated single-fiber microdroplet manipulator that can be used in fields such as the convergence of microdroplets on the output optical field, photodynamic therapy, and optical manipulation. The device consists of a section of dual-core fiber and a liquid-injecting smooth porous surface film at the fiber end. The liquid-injecting smooth porous surface is made of a mixture of a thermosensitive substance and a photosensitive substance, and then an array structure is written by femtosecond laser. Among them, the cladding of the dual-core fiber contains two cores that are centrosymmetric about the center. The light transmitted through the cores is concentrated on a certain area of the liquid-injecting smooth porous surface film at the fiber end after being reflected by the conical frustum at the fiber end. The liquid-injecting smooth porous surface composed of the thermosensitive substance and the photosensitive substance has a photothermal effect. Affected by light illumination, a huge wetting gradient force caused by temperature difference will be generated on the film within 1 second. Then, when the light injection stimulation stops, the instantaneous disappearance of the wetting gradient force will destroy the force balance of the microdroplets on the horizontal liquid-injecting smooth porous surface, causing them to move in a direction towards the heated area.

[0008] For the microdroplets on the liquid-injecting smooth porous surface film at the fiber end, due to the same values of their droplet contact advancing angle (θ A ) and droplet contact receding angle (θ B ), according to the classical wettability gradient force (F wet-grad ) formula, the microdroplets are in a force balance state:

[0009] F wet-grad = r × L × (cosθ A - cosθ B )

[0010] Where r is the surface tension of water, and L represents the length of the microdroplets on the liquid-injecting smooth porous surface film. After starting the narrowband light source, the local temperature of the liquid-injecting smooth porous surface rises rapidly within 1 second. Therefore, the decrease in the droplet contact advancing angle (θ A ) will trigger an asymmetric Laplace force, resulting in the movement of the microdroplets due to the reduction of the surface tension of the injected silicone oil lubricant and the local temperature rise caused by the photothermal effect of the photosensitive substance and the thermosensitive substance.

[0011] The femtosecond laser direct writing technology adopted in the preparation of the liquid injection smooth porous surface has the advantages of ultrashort pulses, ultra-high peak power, and high focusing ability; femtosecond laser direct writing has realized the controllable processing of three-dimensional micro-nano structures of various materials, and shown unique advantages such as easy integration, maskless, arbitrary shape design, high resolution, and applicability to non-planar substrates. The rapid development of femtosecond laser direct writing technology has greatly promoted the preparation and application research of functional metal micro-nano devices.

[0012] The bottom angle θ of the frustum-shaped fiber end of the multi-core fiber satisfies the following relationship:

[0013] θ≥arcsin(n m / n1)

[0014] where n m is the refractive index of the environment around the fiber end, and n1 is the refractive index of multiple fiber cores. When the bottom angle θ of the frustum-shaped fiber end satisfies this condition, when the light wave transmitted in the fiber core passes through this frustum, total internal reflection will occur, so that all the transmitted light waves are converged onto the fiber end face without light leakage, and then the light waves transmitted in each fiber core are strongly converged at the fiber end and react with the liquid injection smooth porous surface film at the fiber end. Optionally, the frustum-shaped fiber end may not satisfy the above relationship and directly coat a reflective film, and at this time the cone angle will not be restricted, so as to collect the light beam more effectively.

[0015] The beneficial effects of the present invention are as follows:

[0016] The present invention combines the advantages of optical fibers and liquid injection smooth porous surfaces, and proposes a micro-droplet manipulation device with a novel structure. By controlling the power and wavelength of the light injected into the fiber core, and changing the different arrangement modes of the fiber cores of the optical fiber, this device can not only realize the directional movement and attitude change of the micro-droplet manipulation, but also make the micro-droplet "dance" (the shape and arrangement mode of the fiber core are as Figure 4 、 5 shown). Taking the spiral and linear distributions as examples: ① For an optical fiber with a spiral distribution of the spatial distribution of the fiber core, light waves are sequentially introduced into the fiber core with a spiral distribution. Affected by different core diameters, the temperature gradient fields generated by the light waves transmitted in different fiber cores on the liquid injection smooth porous surface film at the fiber end are different in size and space, so that the micro-droplet "dances"; ② For an optical fiber with a linear, polygonal, or circular distribution of the spatial distribution of the fiber core, in order to meet specific manipulation requirements, light waves are introduced into some fiber cores, and then the size and power of the injected light waves are controlled to change the light energy converged on the liquid injection smooth porous surface film at the fiber end. Affected by this, the temperature gradient field makes the molecular Brownian motion in the micro-droplet change with temperature. When the temperature rises, the vibration amplitude of the molecules increases, causing the micro-droplet to expand and thus change the attitude of the micro-droplet (the relationship between the height of the micro-droplet and the illumination position is as Figure 8As shown in the figure: 1) When there is no light injection in the fiber core, the microdroplets present a natural posture; 2) When using an optical fiber with a circular or polygonal fiber core shape, or an optical fiber with a linear or polygonal core arrangement, light is injected into the fiber core on one side of the microdroplet edge, causing the microdroplet posture to present a "mouse shape"; 3) When using an optical fiber with an annular core shape, or an optical fiber with a circular core arrangement, light is injected into the fiber cores on both sides of the microdroplet edge, causing the microdroplet posture to present a "mountain shape" that gathers and rises towards the middle; 4) When using an optical fiber with a core arrangement having a middle core, light is injected into the core in the middle of the microdroplet, causing the microdroplet posture to present a "plug shape" that spreads outwards on both sides. The integrated single-fiber microdroplet manipulator with the function of manipulating the motion state and posture of microdroplets overcomes the deficiencies of the traditional liquid injection smooth porous surface, such as low integration, large mechanical wear, and high driving conditions. The fiber end coating structure adopted in the present invention enables the incident light to act on the photosensitive substance on the liquid injection smooth porous surface at the fiber end, thereby generating a wetting gradient force to drive the microdroplets. It has innovations in structure and technology compared with the traditional liquid injection smooth porous surface device. (IV) BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the working principle of an integrated single-fiber microdroplet manipulator.

[0018] Figure 2 It is a schematic diagram of the preparation of the conical end of a multi-core optical fiber: (a) Grinding method; (b) Fused biconical taper method, which consists of a multi-core optical fiber 1, a movable clamping device 17, a fusion unit 18, and a fixed-length cutting 19.

[0019] Figure 3 It is a schematic diagram of the steps for preparing a liquid injection smooth porous surface film based on femtosecond laser.

[0020] Figure 4 The core shape of the optical fiber of an integrated single-fiber microdroplet manipulator can be circular, annular, or polygonal.

[0021] Figure 5 It is a schematic diagram of the spatial distribution of the cores of a multi-core optical fiber: (a) Linear; (b) Polygonal; (c) Circular; (d) Spiral.

[0022] Figure 6 It is a schematic diagram of the array groove structure of the liquid injection smooth porous surface of an integrated single-fiber microdroplet manipulator: (a) Periodic structure; (b) Aperiodic structure.

[0023] Figure 7 It is a schematic diagram of the spatial arrangement of the array groove structure of the liquid injection smooth porous surface of an integrated single-fiber microdroplet manipulator: (a) Grid-shaped distribution; (b) Circular distribution; (c) Circular ring distribution.

[0024] Figure 8It is a schematic diagram of the droplet attitude distribution on the liquid-injecting smooth porous surface film at the fiber end of an integrated single-fiber droplet manipulator under different illumination positions.

[0025] Figure 9 It is a schematic diagram of the system of an integrated single-fiber droplet manipulator. (V) Specific implementation manners

[0026] The present invention will be further described below in conjunction with specific embodiments.

[0027] In conjunction with Figure 1 , the implementation manner of the present invention mainly provides an integrated single-fiber droplet manipulator. Its characteristics are: the device is composed of a multi-core optical fiber (1), the multi-core optical fiber (1) includes a cladding (2) and a core (3), the fiber end of the multi-core optical fiber (1) is ground to form a conical frustum fiber end (4), and there is a liquid-injecting smooth porous surface film (7) with an array of groove structures (6) on the end face (5) of the conical frustum fiber end (4). A photosensitive material (8) is doped in the liquid-injecting smooth porous surface film (7), and a lubricant (9) is filled in the array of groove structures (6); on the one hand, the light wave (10) transmitted by the core (3) forms a converging light wave (11) after being reflected by the conical frustum fiber end (4). Due to the photothermal effect, the converging light wave (11) is absorbed by the photosensitive material (8) after being transmitted to the liquid-injecting smooth porous surface film (7) and converted into heat energy. Therefore, a temperature gradient field (12) is formed in the area irradiated by the converging light wave (11). By controlling the power of the light injected into the core (3), the size and spatial distribution of the temperature gradient field (12) can be controlled; on the other hand, the droplet (13) attached to the liquid-injecting smooth porous surface film (7) generates a wetting gradient force (14) under the influence of the temperature gradient field (12). Under the action of the wetting gradient force (14), the attitude of the droplet (13) will change and generate directional sliding, and finally the droplet (13) is manipulated under the action of different temperature gradient fields (12).

[0028] Taking a two-core optical fiber as an example, the preparation process of an integrated single-fiber droplet manipulator can be divided into the following two steps:

[0029] Step 1. Preparation of the conical frustum fiber end (such as Figure 2As shown in the figure. Method 1: Take a section of the dual-core optical fiber and fix it with an optical fiber fixture (15), then place the fiber end on the polishing disc (16). The optical fiber fixture (15) and the optical fiber polishing disc (16) are respectively connected to their own DC motors. By controlling the optical fiber fixture (15) to rotate self-spinning at an angle θ with the normal of the polishing disc (16), a conical fiber end with an opening angle of θ is prepared. Method 2: Fix the optical fiber on the optical fiber taper machine with a movable clamping device (17), melt it under the high-temperature heating of the fusion unit (18), and stretch it to both sides at the same time. Different-length cones are obtained through melting and tapering, and then a fixed-length cutting (19) is performed at an appropriate position in the tapering area to prepare conical fiber ends with different opening angles.

[0030] Step 2: Preparation of the smooth porous surface film with liquid injection at the fiber end (as Figure 3 shown in the figure). Here, the femtosecond laser direct writing technology will be used for preparation: The first step: First, mix and stir evenly the liquid solution of the smooth porous surface with liquid injection (such as PDMS) and the photosensitive substance (such as Fe3O4), then pour the mixed solution (20) into a self-made mold, and perform self-leveling and bubble removal in a vacuum furnace. After that, high-temperature annealing can be carried out to make a flexible smooth porous surface film with liquid injection. The second step: After cutting the smooth porous surface film with liquid injection prepared in the previous step into a circular shape, place the smooth porous surface film with liquid injection on the stage, adjust the stage of the three-dimensional moving precision translation stage through the computer, adjust the relative position of the femtosecond laser focus line and the film, and then set the scanning speed of the three-dimensional moving precision translation stage, the incident femtosecond laser optical power, the polarization state of the femtosecond laser, and the distance between the femtosecond laser focus line and the film surface, and an array structure can be written on the film surface. The third step: Finally, with the help of capillary action, silicone oil (21) is injected onto the smooth porous surface with liquid injection written by the femtosecond laser to manufacture a smooth porous surface film with liquid injection that meets the requirements. Apply a high-transparency thermosetting epoxy resin glue (22) evenly on the polished end face of the dual-core optical fiber, connect the smooth porous surface film template with liquid injection to the optical fiber end face, and wait until it is heated to a viscous state, then adjust the distance between the smooth porous surface film template with liquid injection and the optical fiber end face to ensure that the film, the glue, and the optical fiber end face are in close contact. Finally, heat the thermosetting epoxy resin glue until it is completely cured to fix the film on the optical fiber end face to complete the preparation of the smooth porous surface film with liquid injection.

[0031] The following will further elaborate on the present invention in combination with specific embodiments.

[0032] Step 1: Preparation of the optical microdroplet manipulator: Prepare an integrated single-fiber optical microdroplet manipulator according to the steps of realizing the optical fiber end grinding and the preparation of the smooth porous surface film with liquid injection at the fiber end in the implementation manner.

[0033] Step 2: Optical signal input (as Figure 9As shown in the figure. The optical signal input of an integrated single-fiber droplet manipulator is the optical signal emitted by a narrowband light source laser, which is input into the optical power control module after passing through a 1×2 coupler. We control the magnitude of the optical power output by the optical power control module through a computer, and finally the optical signal is input into the fiber core from the optical power control module.

[0034] Step 2: Manipulation of droplets (as Figure 9 shown in the figure). The control computer adjusts the optical power module to control the wavelength and optical power of the light wave transmitted into the fiber core. The light wave transmitted by the fiber core is concentrated in a partial area of the smooth porous surface film of the liquid injection after being reflected by the conical fiber end. Affected by the converging light wave, a photothermal effect is generated on the smooth porous surface of the liquid injection doped with a photosensitive material. A huge wetting gradient force caused by the temperature difference will be generated on the film within 1 second, making the droplets on the smooth porous surface film of the liquid injection on the fiber end change due to their droplet contact advancing angle (θ A ) and droplet contact receding angle (θ B ), breaking the force balance state and making it start to move directionally. When using an integrated single-fiber droplet manipulator to control smaller droplets, when the power of the transmitted light wave is increased, the light energy converging on the smooth porous surface film of the fiber end is enhanced. Affected by this, the wetting gradient force generated by the temperature gradient field increases the difference between the droplet contact advancing angle (θ A ) and the droplet contact receding angle (θ B ) of the droplet, thereby accelerating the movement speed of the droplet; when using an integrated single-fiber droplet manipulator to control larger droplets, when the power of the transmitted light wave is increased, the light energy converging on the smooth porous surface film of the fiber end is enhanced, and the intensity of the temperature gradient field increases. Affected by this, the molecular Brownian motion in the droplet will change with the temperature. When the temperature rises, the vibration amplitude of the molecules increases, causing the droplet to expand and then change the posture of the droplet. Through the feedback signal fed back to the computer by the optical power module, a distribution map of the influence of different illumination positions on the droplet posture can be obtained.

Claims

1. An integrated single-fiber microdroplet manipulator, characterized in that: The described integrated single-fiber microdroplet manipulator is composed of a multi-core optical fiber (1). The multi-core optical fiber (1) includes a cladding (2) and a core (3). The fiber end of the multi-core optical fiber (1) is ground to form a conical frustum fiber end (4). There is a liquid injection smooth porous surface film (7) with an array of groove structures (6) on the end face (5) of the conical frustum fiber end (4). A photosensitive material (8) is doped in the liquid injection smooth porous surface film (7), and a lubricant (9) is filled in the array of groove structures (6). On the one hand, the light wave (10) transmitted by the core (3) forms a converging light wave (11) after being reflected by the conical frustum fiber end (4). Due to the photothermal effect, the converging light wave (11) is absorbed by the photosensitive material (8) after being transmitted to the liquid injection smooth porous surface film (7) and converted into heat energy. Therefore, a temperature gradient field (12) is formed in the area irradiated by the converging light wave (11). By controlling the power of the light injected into the core (3), the magnitude and spatial distribution of the temperature gradient field (12) can be controlled. On the other hand, the microdroplets (13) attached to the liquid injection smooth porous surface film (7) generate a wetting gradient force (14) under the influence of the temperature gradient field (12). Under the action of the wetting gradient force (14), the attitude of the microdroplets (13) will change and produce directional sliding. Finally, the manipulation of the microdroplets (13) is achieved under the action of different temperature gradient fields (12).

2. The preparation method of the integrated single-fiber microdroplet manipulator according to claim 1 is as follows: 1) Take a multi-core optical fiber and fix it with an optical fiber fixture. Then place the fiber end on a grinding disc. Both the optical fiber fixture and the optical fiber grinding disc can rotate around their respective central axes. By controlling the angle between the helical dual-core optical fiber and the normal of the grinding disc surface, conical frustum fiber ends with different opening angles can be prepared. Or the optical fiber can be fixed on an optical fiber tapering machine, melted under high-temperature heating, and stretched simultaneously to both sides. By melting and tapering, cones with different lengths are obtained, and then cut at a suitable position in the tapered area to prepare conical frustum fiber ends with different opening angles. 2) First, mix and stir evenly the liquid solution of the liquid injection smooth porous surface and the photosensitive material, then pour the mixture into a self-made mold, and perform self-leveling and degassing in a vacuum furnace. After that, high-temperature annealing is carried out to make a flexible liquid injection smooth porous surface. 3) After cutting the liquid injection smooth porous surface prepared in the previous step into a circle, use femtosecond laser to engrave an array structure on its surface. 4) Finally, with the help of capillary action, silicone oil is injected onto the liquid injection smooth porous surface engraved by femtosecond laser to manufacture a liquid injection smooth porous surface that meets the requirements.

3. The integrated single-fiber droplet manipulator according to claim 1, wherein The number of cores of the multi-core optical fiber is greater than or equal to 1.

4. An integrated single-fiber droplet manipulator according to claim 1, characterized in that, The shape of the core of the multi-core optical fiber is one of circular, annular, and polygonal.

5. An integrated single-fiber droplet manipulator according to claim 1, wherein, The spatial distribution of the cores of the multi-core optical fiber is one of linear, polygonal, circular, and spiral distributions.

6. An integrated single-fiber microdroplet manipulator according to claim 1, characterized in that: The described microdroplets are one of tiny liquid droplets and tiny bubbles.

7. An integrated single-fiber droplet manipulator according to claim 1, characterized in that: The described array of groove structures is one of periodic structures and non-periodic structures.

8. An integrated single-fiber microdroplet manipulator according to claim 1, characterized in that: The spatial arrangement of the described array of groove structures is one of grid-shaped distribution, circular distribution, and circular ring distribution.

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