Method for controlling directional transportation of liquid drops in two-dimensional nano channel

Abstract

The invention discloses a method for controlling directional transportation of liquid drops in a two-dimensional nano channel. Establishing a two-dimensional nano channel and a nano probe, and constructing a droplet model; the mass center of the nano liquid drop is restrained, atoms on the two sides of the x-axis edge of the graphene sheet are fixed, and the nano channel is kept in a fixed state; the simulation system is optimized, system energy is reduced, and the initial configuration of the simulation system tends to be stable; in a molecular dynamics simulation process, setting boundary conditions of three dimensions as periodic boundary conditions; calculating the time integral of the Newton motion equation; controlling the temperature of the system, keeping the temperature, and enabling the relaxation of the system to reach a steady state; the nanoprobe is pressed down, so that the graphene sheet on the upper layer of the two-dimensional nanochannel is deformed, and the non-parallel two-dimensional nanochannel is constructed; the limitation on the mass center of the nano liquid drop is relieved, and the movement behavior of the nano liquid drop is observed; according to the method, the movement behavior of the liquid drop at the nanoscale can be analyzed from the aspects of atoms and molecules.

Description

Technical Field

[0001] The invention relates to the field of directional droplet transport, and in particular to a method for controlling directional droplet transport in a two-dimensional nanochannel. Background Art

[0002] Directed droplet transport technology has shown broad prospects in the fields of oil-water separation, water collection, and heat transfer. With the development of science and technology, the research scale has been reduced to the nanoscale, and driving nanodroplets for directional transport has shown great potential in engineering applications. Most directional transport of droplets is achieved by applying an external field, which requires continuous energy from the outside world, has strict conditions, and high energy consumption, which limits its development. Therefore, spontaneously driving droplet directional transport through surface wettability gradients or structural gradients has become a research focus.

[0003] At present, the research on directional transport of droplets is mainly focused on two-dimensional planes, while the directional transport of droplets in nanochannels has not been widely studied. Limited by the size and shape of nanochannels, the movement of droplets may show different behaviors and states. Although some progress has been made in the research on directional transport of droplets in one-dimensional nanochannels, its defects affect its application. Therefore, the development of directional transport technology for droplets in two-dimensional nanochannels has broad prospects.

[0004] In summary, the spontaneous directional transport of droplets in two-dimensional nanochannels needs to be studied urgently. Due to the nanoscale, the motion state of droplets in nanochannels is completely different from the macroscopic state, and new methods are needed to study it. Molecular dynamics methods can accurately simulate and manipulate the motion of droplets at the nanoscale, so it has become one of the main tools for studying the motion of nanodroplets and the flow of nanofluids. Molecular dynamics simulation can be used to deeply study the spontaneous transport behavior of droplets in two-dimensional nanochannels, provide a reasonable explanation for the motion phenomenon in the macroscopic state, and be applied to engineering fields such as oil-water separation, water collection, and heat transfer. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention proposes a method for controlling the directional transport of droplets in a two-dimensional nanochannel.

[0006] A method for controlling directional transport of droplets in a two-dimensional nanochannel comprises the following steps:

[0007] Building two-dimensional nanochannels and nanoprobes;

[0008] Constraining the center of mass of the nanodroplet and fixing the atoms on both sides of the graphene sheet keeps the nanochannel fixed;

[0009] Using nanoindentation technology, the nanoprobe is pressed down to deform the graphene sheet on the two-dimensional nanochannel, thereby constructing a non-parallel two-dimensional nanochannel; then, the restriction on the center of mass of the nanodroplet is released.

[0010] Preferably, the two-dimensional nanochannel comprises two layers of graphene sheets.

[0011] Preferably, the nanodroplets are of SPC / E configuration.

[0012] Preferably, the nanoprobes comprise silicon atoms.

[0013] Preferably, the size of the graphene sheet is The distance between graphene sheets is

[0014] An experimental method for controlling directional transport of droplets in a two-dimensional nanochannel comprises the following steps:

[0015] Establish two-dimensional nanochannels and nanoprobes in the molecular dynamics simulation system, and then construct a droplet model;

[0016] The center of mass of the nanodroplet is constrained, and the atoms on both sides of the edge of the graphene sheet along the x-axis are fixed so that the nanochannel remains fixed, and the silicon nanoprobe is placed directly above the two-dimensional nanochannel;

[0017] During the molecular dynamics simulation, the conjugate gradient method is used to optimize the simulation system, reduce the system energy, and make the initial configuration of the simulation system tend to a steady state; the boundary conditions of the three dimensions are all set as periodic boundary conditions; the initial position and velocity are set, the potential function and force field are set, the resultant force and acceleration of the particles are calculated, the equation of motion is solved to calculate the position and velocity of the particles in the next step, and the particle position, velocity, acceleration and interaction potential energy are output. The simulation ends when the set step length is reached; the time integral of Newton's equation of motion is calculated; the system is temperature-controlled and maintained to relax the system to a steady state;

[0018] Using nanoindentation technology, the nanoprobe is pressed down on the basis of the optimized model, causing the graphene sheet on the upper layer of the two-dimensional nanochannel to deform, thereby constructing a non-parallel two-dimensional nanochannel; then, the restriction on the center of mass of the nanodroplet is released, and the movement behavior of the nanodroplet is observed under the NVE ensemble.

[0019] Preferably, the relaxation time is 0.5 ns.

[0020] Preferably, the time step size of the Newton's equation of motion is 1fs.

[0021] Preferably, the maintained temperature is 298K.

[0022] The above method is used in separating oil and water in a mixed liquid, collecting moisture from the air, collecting and guiding water droplets from various surfaces, and heat dissipation of equipment.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. Atomic-level analysis: Through molecular dynamics simulation technology, the movement behavior of droplets at the nanoscale can be analyzed from the perspective of atoms and molecules, and its specific movement mechanism can be understood, making up for the lack of understanding of the internal mechanism in macroscopic experiments.

[0025] 2. No need to construct a specific flow channel: The innovative combination of nanoindentation technology and droplet directional transport technology can achieve directional transport of nanodroplets without the need to construct a specific fluid channel. It has a simple structure, is easy to operate, and has low energy consumption.

[0026] 3. Wide applicability: This method is not only applicable to two-dimensional nanochannels composed of graphene sheets, but also effective for two-dimensional nanochannels based on other materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 is a molecular dynamics simulation flow chart of the present invention;

[0029] Figure 2 It is the side view of the molecular dynamics model and the droplet displacement diagram of the nanoprobe at different falling heights in the example;

[0030] Figure 3 is the droplet displacement diagram for different drop heights of the nanoprobe in the example;

[0031] Figure 4 is the droplet displacement diagram when the nanoprobe slides in the example;

[0032] Figure 5 It is a schematic diagram of the movement of the nanoprobe in a two-dimensional plane in the example;

[0033] Figure 6 It is a diagram of the displacement of the droplet along the predetermined trajectory in the example. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The present invention adopts molecular dynamics simulation technology, preferably uses Materials Studio software and Packmol software for modeling, and uses LAMMPS software for simulation. The molecular dynamics simulation verifies that the nanoindentation technology controls the directional transport of droplets in two-dimensional nanochannels, providing a new method.

[0036] The molecular dynamics simulation technology flow chart used in the present invention is shown in the attached Figure 1 As shown. First, set the initial position and initial velocity of the particle, select a suitable potential function to represent the force between particles, and set the potential function and force field. Then, use the finite difference method to solve the Newtonian equation of motion for the particle motion, calculate the resultant force and acceleration of the particle, and obtain the trajectory of the particle motion. Next, solve the equation of motion to calculate the position and velocity of the particle in the next step, and use the method of statistical mechanics to obtain the physical parameters such as displacement, velocity, acceleration, and interaction potential energy of the particle motion, and output the position and velocity of the particle. If the set step length is reached, the simulation ends. If the set step length is not reached, return to calculating the resultant force and acceleration of the particle.

[0037] Specifically, the present invention provides a method for controlling directional transport of droplets in a two-dimensional nanochannel, which mainly includes the following steps:

[0038] 1) Establish a two-dimensional nanochannel model and a nanoprobe model in Materials Studio software. The two-dimensional nanochannel consists of two layers of The distance between two graphene sheets is The nanoprobe is composed of silicon atoms and adopts a cylindrical configuration. A droplet model is established in Packmol software, and the droplet model adopts an SPC / E configuration.

[0039] 2) At the initial moment, in order to prevent thermodynamic fluctuations, the center of mass of the nanodroplet is constrained to prevent the droplet from moving freely. In order to keep the two-dimensional nanochannel stable under nanoindentation, the atoms on both sides of the edge of the graphene sheet along the x-axis in the two-dimensional nanochannel are fixed so that the channel always remains fixed. The silicon nanoprobe is placed directly above the two-dimensional nanochannel.

[0040] 3) During the molecular dynamics simulation, the conjugate gradient method is used to minimize the energy and optimize the simulation system so that the system reaches a steady state. The number of optimization steps of the conjugate gradient method each time is 100 to 1000 steps.

[0041] 4) During the molecular dynamics simulation, due to thermodynamic fluctuations, some water molecules will evaporate and detach from the droplets to move freely. In order to prevent the boundary from affecting the detached water molecules, the boundary conditions in the three dimensions are set as periodic boundary conditions.

[0042] 5) During the molecular dynamics simulation, the Velocity-Verlet algorithm with higher accuracy and better efficiency is used to calculate the time integral of Newton's equation of motion, and the time step is taken as 1 fs.

[0043] 6) During the molecular dynamics simulation, the simulation system was relaxed using the NVT ensemble with a relaxation time of 0.5 ns, and the secondary simulation system was optimized. The system was temperature controlled using a Nosé-Hoover thermostat to maintain the temperature at room temperature 298 K.

[0044] 7) After optimizing the simulation system, the nanoprobe is pressed down using nanoindentation technology to deform the graphene sheet on the upper layer of the two-dimensional nanochannel, thereby constructing a non-parallel two-dimensional nanochannel. Then, the restriction on the center of mass of the nanodroplet is released, and the system is placed in the NVE ensemble to observe the motion behavior of the nanodroplet.

[0045] The following is a detailed description of a method for controlling directional transport of droplets in a two-dimensional nanochannel proposed by the present invention in conjunction with examples. However, the examples below should not be construed as limiting the scope of protection of the present invention.

[0046] As attached Figure 2 As shown, the two-dimensional nanochannel consists of two layers with a size of The two graphene sheets are composed of The two sides of the parallel two-dimensional nanochannel are fixed, and the cylindrical probe is placed directly above the nanochannel. Since graphene has a high elastic modulus, the downward movement of the probe will induce deformation of the graphene, forming a non-parallel structure. The probe descends to a height of h. Due to the deformation of the upper graphene sheet, structures similar to non-parallel two-dimensional nanochannels are formed on the left and right sides. In non-parallel two-dimensional nanochannels, since the contact area between the droplet and the narrower end of the nanochannel is larger, its interaction potential energy with the narrower end of the nanochannel is lower, so the droplet always tends to move toward the narrower end of the non-parallel nanochannel, realizing directional transport of the droplet.

[0047] The probe's descending height can change the deformation of the upper graphene sheet, causing the angle of the nanochannels on both sides to change. Therefore, it is necessary to study its effect on the spontaneous transport of droplets in the channel. For comparison, four different descending heights (respectively) were selected. and ) to simulate, the model is as shown in the attached Figure 2 The results show that after the center of mass constraint of the droplet is released, the droplet can achieve spontaneous movement in the channel where the nanoindentation is applied, as shown in the attached Figure 3 As shown. When the probe drops When , no non-parallel two-dimensional nanochannels are formed, so the droplets do not move in a directional manner. Due to thermodynamic fluctuations, the droplets move irregularly. When the probe is lowered, the average speed of the droplet increases as the probe descends. When the probe descends, the deformation of the upper graphene sheet increases, and the angle of the non-parallel two-dimensional nanochannels formed also increases, resulting in a greater driving force on the droplet. When the angle of the nanochannel is large enough, the average speed of the droplet movement remains almost unchanged. The forces acting on the droplet are mainly driving force and friction. When the channel angle is small, as the droplet moves toward the narrower end of the channel, the nanodroplet is less compressed. Therefore, the contact area between the droplet and the inner surface of the nanochannel is small, and the friction force that hinders movement is also small, so the average speed of the droplet increases faster. As the channel angle increases, the degree of compression of the droplet also increases, resulting in a larger contact area between the droplet and the channel, and therefore a larger friction force. The competition between the driving force and the friction force determines that the average speed of the droplet will not continue to increase with the increase in the angle. These results prove that nanoindentation technology can achieve spontaneous transport of droplets in nanochannels, and the nanoindentation depth can regulate the average speed of droplet movement.

[0048] The probe can slide on the surface of the material to detect its surface morphology. Therefore, it is possible to consider regulating the direction of the droplet's movement and the start and end of the movement by the sliding of the probe. By applying different motion behaviors to the probe at different time periods, the manipulation of the motion of the nanodroplet by the sliding of the probe was studied. According to the direction of the probe's movement, the specific motion behavior of the droplet is divided into four periods. As shown in the attached figure Figure 4 As shown in the figure, within 0ps-500ps, the probe moves downward, the graphene nanosheet deforms, and a non-parallel two-dimensional nanochannel is formed. The droplet begins to move spontaneously toward the narrower end and finally stabilizes at the probe indentation. Within 500ps-700ps, the probe slides to the right, and the narrowest end of the nanochannel also moves to the right. Since the droplet tends to move toward the narrowest end of the channel, the droplet continues to move to the right to the probe indentation. Within 700ps-900ps, the probe begins to slide to the left, and the narrowest end of the nanochannel also moves to the left, and the droplet begins to move in the opposite direction to the probe indentation. After 900ps, since the probe remains fixed, the droplet is always stable at the probe indentation. The above phenomenon shows that the movement direction of the droplet can be guided and the stable position of the droplet can be controlled by sliding the probe.

[0049] In order to realize the movement of droplets in any direction, the sliding of the probe is extended to the two-dimensional plane. Figure 5 In this simulation, the nanochannel consists of The probe is a spherical indenter. At the initial moment, the droplet is placed in the center of the nanochannel, and the probe slides along the specified track, as shown in the direction of the arrow. When the probe is pressed down along the z direction, the upper graphene layer will deform, and the nanochannel will form a non-parallel nanochannel locally. According to previous studies, nanodroplets tend to move toward the narrower end of the nanochannel, so the droplet will theoretically move with the sliding of the probe. As shown in the attached figure Figure 6 As shown in the figure, the displacement trajectory of the droplet has the same movement direction as the sliding trajectory of the probe, indicating that the droplet can move along the movement of the probe in a two-dimensional plane. It can be concluded that the movement of the droplet along any trajectory can be achieved by sliding the probe, thus realizing the programmable operation of the droplet. This research plays an important role in many occasions where precise control of droplet movement is required, and can provide a reference for the development of future nanorobots.

[0050] The method of controlling the directional transport of droplets in two-dimensional nanochannels has many applications, especially in oil-water separation, water collection and heat transfer.

[0051] Oil-water separation: By applying a physical gradient in a two-dimensional nanochannel, droplets (such as water or oil) can be induced to move in a specific direction. This directional transport can be used to separate oil and water in a mixed liquid, thereby achieving efficient oil-water separation, especially when dealing with complex emulsions; using the surface tension effect and capillary force in the nanochannel to drive the movement of droplets can significantly reduce the energy consumption in the separation process.

[0052] Water collection: Through the design of surface structures in nanochannels, water droplets can move and gather along a predetermined path. This is very effective in collecting moisture from the air or collecting and guiding water droplets from various surfaces; using directional transport in nanochannels, tiny water droplets can be quickly collected into a larger storage area, thereby improving the efficiency of water collection.

[0053] Heat transfer: Directed transport of droplets can be used to efficiently transfer heat in devices through nanochannels. For example, by controlling the movement of droplets, the liquid can be quickly guided to evaporate and take away heat in the heat dissipation area, thereby improving the heat dissipation efficiency of the device; at the nanoscale, the movement of droplets can be very precisely controlled, which means that more precise heat distribution can be achieved during the heat transfer process, which is suitable for thermal management of microelectronic devices or other precision equipment.

[0054] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0055] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for controlling directional transport of droplets in a two-dimensional nanochannel, characterized in that: The following steps are involved: Building two-dimensional nanochannels and nanoprobes; Constraining the center of mass of the nanodroplet and fixing the atoms on both sides of the graphene sheet keeps the nanochannel fixed; Using nanoindentation technology, the nanoprobe is pressed down to deform the graphene sheet on the two-dimensional nanochannel, thereby constructing a non-parallel two-dimensional nanochannel; then, the restriction on the center of mass of the nanodroplet is released.

2. The method for controlling directional transport of droplets in a two-dimensional nanochannel according to claim 1, characterized in that: The two-dimensional nanochannel includes two layers of graphene sheets.

3. The method for controlling directional transport of droplets in a two-dimensional nanochannel according to claim 1, characterized in that: The nanodroplets are of SPC / E configuration.

4. The method for controlling directional transport of droplets in a two-dimensional nanochannel according to claim 1, characterized in that: The nanoprobes include silicon atoms.

5. The method for controlling directional transport of droplets in a two-dimensional nanochannel according to claim 1, characterized in that: The size of the graphene sheet is The distance between graphene sheets is 6. An experimental method for controlling directional transport of droplets in a two-dimensional nanochannel, characterized in that: The following steps are involved: Establish two-dimensional nanochannels and nanoprobes in the molecular dynamics simulation system, and then construct a droplet model; The center of mass of the nanodroplet is constrained, and the atoms on both sides of the edge of the graphene sheet along the x-axis are fixed so that the nanochannel remains fixed, and the silicon nanoprobe is placed directly above the two-dimensional nanochannel; During the molecular dynamics simulation, the conjugate gradient method is used to optimize the simulation system, reduce the system energy, and make the initial configuration of the simulation system tend to a steady state; the boundary conditions of the three dimensions are all set as periodic boundary conditions; the initial position and velocity are set, the potential function and force field are set, the resultant force and acceleration of the particles are calculated, the equation of motion is solved to calculate the position and velocity of the particles in the next step, and the particle position, velocity, acceleration and interaction potential energy are output. The simulation ends when the set step length is reached; the time integral of Newton's equation of motion is calculated; the system is temperature-controlled and maintained to relax the system to a steady state; Using nanoindentation technology, the nanoprobe is pressed down on the basis of the optimized model, causing the graphene sheet on the upper layer of the two-dimensional nanochannel to deform, thereby constructing a non-parallel two-dimensional nanochannel; then, the restriction on the center of mass of the nanodroplet is released, and the movement behavior of the nanodroplet is observed under the NVE ensemble.

7. The experimental method for controlling directional transport of droplets in a two-dimensional nanochannel according to claim 6, characterized in that: The relaxation time is 0.5 ns.

8. The experimental method for controlling directional transport of droplets in a two-dimensional nanochannel according to claim 6, characterized in that: The time step size of the Newton equations of motion is 1 fs.

9. The experimental method for controlling directional transport of droplets in a two-dimensional nanochannel according to claim 6, characterized in that: The maintained temperature is 298K.

10. Use of the method according to any one of claims 1 to 5 in separating oil and water in a mixed liquid, collecting moisture from the air, collecting and guiding water droplets from various surfaces, and heat dissipation of equipment.

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