Microfluidically synthesized ferrofluid microcapsule as well as preparation method and application thereof

Abstract

The invention relates to a microfluidic synthesized ferrofluid microcapsule, a preparation method and application thereof, preparation raw materials of the microcapsule comprise an inner phase, an intermediate oil phase and an outer phase, the inner phase is composed of oil-based ferrofluid Fe3O4, the intermediate oil phase is 1, 6-hexanediol diacrylate, and the outer phase is a water phase added with polyvinyl alcohol and # imgabs0 # F108; according to the technical scheme provided by the invention, the ferrofluid microcapsule which is synthesized in a micro-fluidic manner and is good in heat dissipation efficiency, not easy to aggregate and settle and easy in flowability control is prepared by combining a micro-fluidic device and a micro-fluidic technology with a three-phase material with specific components.

Description

Technical Field

[0001] The present application relates to the technical field of microfluidic microcapsules, and in particular to a microfluidic synthesized ferrofluid microcapsule, a preparation method and application thereof. Background Art

[0002] Ferrofluids are advanced smart materials consisting of magnetic nanoparticles dispersed in a carrier liquid (which can be water-based or oil-based). These nanoparticles are usually made of ferromagnetic materials such as iron, nickel or cobalt, and are coated with surfactants to prevent the particles from aggregating in the carrier liquid. As colloidal suspensions, ferrofluids have significant magnetic response and rheological properties, and show obvious physical and chemical changes under the action of an external magnetic field. In addition, ferrofluids also exhibit superparamagnetism, which enables them to respond rapidly and reversibly to an external magnetic field, while retaining no residual magnetism after the magnetic field is removed. This property makes ferrofluids widely applicable in advanced technology applications such as magnetic seals, vibration reduction systems, and biomedical imaging and drug delivery. The stability of ferrofluids is affected by many factors, including temperature, pH value and magnetic field strength.

[0003] Due to the colloidal suspension properties of magnetic nanoparticles, ferrofluids exhibit remarkable controllable fluidity and thermal conductivity under the action of an applied magnetic field. These unique thermophysical properties have stimulated extensive research interest in the fields of thermal management and heat dissipation applications. Ferrofluids can achieve adjustable thermal conductivity and directional heat transfer through the chain arrangement of nanoparticles by magnetic fields, thereby significantly improving the efficiency of heat conduction. Therefore, ferrofluids are considered to be a strong candidate for improving the heat transfer efficiency of advanced cooling systems, especially in electronic devices and optical components with high heat flux density. By applying magnetic fields to dynamically control and optimize the fluid flow path, effective thermal management can be achieved, thereby improving the overall heat dissipation performance of the system, reducing the operating temperature of key components, and improving reliability and operating efficiency. In addition, combining magnetic field control with advanced fluid dynamics can achieve precise thermal conductivity and heat distribution at the microscale, paving the way for the development of innovative smart thermal management solutions. However, despite the many advantages of ferrofluids, their widespread practical application still faces several major challenges. The main problems include particle sedimentation, aggregation, and fluidity control. Sedimentation refers to the gradual sinking of magnetic nanoparticles under the action of gravity, resulting in non-uniformity of fluid properties and reduced functional efficiency. Aggregation intensifies sedimentation due to the magnetic attraction between particles and weakens the magnetic responsiveness of the fluid. In addition, an external magnetic field may change the viscosity of the ferrofluid, making flow control more difficult and may increase flow resistance, thereby increasing the operational complexity in practical applications. These challenges together lead to a gradual degradation of performance over time, limiting the feasibility of ferrofluids in various engineering and industrial environments.

[0004] The rapid development of electronic technology has driven widespread applications in consumer electronics, data centers, and supercomputing. However, the performance improvement of electronic devices is accompanied by significant power consumption and heat generation, which are key factors affecting the reliability and life of electronic components. Mithal et al. observed that for every 1°C increase in temperature, the chip failure rate increased by 4%, while a 10°C temperature reduction significantly reduced the failure rate. Phase change cooling, as a passive thermal management method, has attracted widespread attention due to its simplicity and cost-effectiveness. It uses the latent heat released by phase change materials (PCMs) during the phase change process to regulate the temperature. However, traditional PCMs (such as paraffin with a thermal conductivity of less than 1W / (m·K)) are challenging to provide continuous cooling for the entire heat generation cycle of electronic devices. In addition, PCM-based cooling is ineffective before the phase change temperature is reached and after the phase change is completed, limiting its applicability in long-term high-performance scenarios. To overcome these limitations, the introduction of ferrofluid microcapsules has become a promising alternative. Encapsulating magnetic fluids in a protective shell made of polymers, lipids, or inorganic substances can enhance their thermal stability and alleviate performance degradation caused by sedimentation and aggregation during storage and operation. The encapsulation process maintains the intrinsic properties of the magnetic fluid and enables customization of functionality through chemical engineering of the shell material. Advanced microencapsulation techniques, such as emulsion polymerization and interfacial polymerization, combined with microfluidics, further improve the uniformity and functionality of these materials. Microfluidics systems, with their precision in controlling fluid behavior, can generate complex double emulsion droplets, such as water-in-oil-in-water (W / O / W) structures, optimize interface arrangements and enhance heat transfer performance. These innovations provide a solid framework for the development of next-generation passive cooling solutions that can provide durable and efficient thermal management for high-performance electronic devices. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present application provides a microfluidic synthesized ferrofluid microcapsule which has good heat dissipation efficiency and is not prone to aggregation and sedimentation, prepared by combining a microfluidic device and technology with a three-phase material of specific composition.

[0006] In order to solve the above technical problems, the technical solution adopted in the present application is: a microfluidic synthesis ferrofluid microcapsule, the preparation raw materials of the microcapsule include an inner phase, an intermediate oil phase and an outer phase, the inner phase is composed of an oil-based ferrofluid Fe 3 O 4 The composition is that the intermediate oil phase is 1,6-hexanediol diacrylate (HDDA), and the external phase is added with polyvinyl alcohol (PVA) and The aqueous phase of F108.

[0007] Furthermore, the oil-based ferromagnetic fluid Fe 3 O 4 Composition: Fe 3 O4 Nanoparticles, silicone oil and stabilizer (the "oil-based ferrofluid Fe3O4" herein can be purchased from the market as a whole).

[0008] Furthermore, the molecular weight of the polyvinyl alcohol is 13000-23000, and the degree of hydrolysis is 87-89%; it can be purchased from Sigma-Aldrich Co., Ltd.; F108 can also be purchased from Sigma-Aldrich Co., Ltd.

[0009] Furthermore, the mass percentage of the polyvinyl alcohol in the aqueous phase (with water as solvent) is 5-10%, and the The mass percentage of F108 in the water phase is 1-3%.

[0010] Furthermore, the mass percentage of the polyvinyl alcohol in the water phase is 8%, and the The mass percentage of F108 in the water phase is 2%.

[0011] Furthermore, the flow rate of the inner phase is 5-15uL / min.

[0012] Furthermore, the flow rate of the intermediate oil phase is 10-20uL / min.

[0013] Furthermore, the flow rate of the external phase is 900-1200uL / min.

[0014] The present application also provides a method for preparing the above-mentioned microfluidic synthesized ferrofluid microcapsules, comprising:

[0015] (1) First, prepare the oil-based ferrofluid Fe 3 O 4 The internal phase is composed of 1,6-hexanediol diacrylate (HDDA) and the intermediate oil phase is added with polyvinyl alcohol (PVA) and F108's foreign minister;

[0016] (2) A needle-based microfluidic multiphase flow system is used, the system comprises a main pipeline, the main pipeline is further provided with a first branch pipe and a second branch pipe; one end of the main pipeline is a feed end, and the other end is a discharge end, the feed end is used for inputting the inner phase; at least one first branch pipe is provided along the radial direction of the main pipeline, for inputting the intermediate oil phase; two second branch pipes are symmetrically provided along the radial direction of the main pipeline, both for inputting the outer phase; the inner phase, the intermediate oil phase and the outer phase prepared in step (1) are respectively inputted from the corresponding ports of the needle-based microfluidic multiphase flow system, and then the three-phase material finally flows out from the discharge end of the main pipeline;

[0017] (3) During the output process of the main pipeline, the OMF-HDDA microcapsules are cured under ultraviolet (UV) irradiation to obtain OMF-HDDA microcapsules.

[0018] Furthermore, the first branch pipe and the second branch pipe are arranged in sequence from the feed end to the discharge end of the main pipeline.

[0019] Furthermore, the wavelength of the ultraviolet rays used for curing is 365 mm.

[0020] Furthermore, the diameter of the OMF-HDDA microcapsules is 400-600 μm.

[0021] Furthermore, the feeding sequence is first the external phase, then the middle phase oil phase, and finally the internal phase, and the interval time between feeding each phase is controlled at 0.5-1.5min.

[0022] The present application also provides a heating system for ferrofluid microcapsules synthesized by microfluidic preparation as described above, the system comprising an insulating body, a receiving groove for receiving a phase change material container being arranged in the insulating body, the phase change material container being placed in the receiving groove, a copper plate being arranged between the receiving groove and the phase change material container, a plurality of needle-shaped fins extending in the thickness direction being arranged in the phase change material container, ferrofluid microcapsules being placed in the phase change material container, and the ferrofluid microcapsules covering the needle-shaped fins.

[0023] The present application also provides a method for performing thermal simulation using the above heating system, comprising:

[0024] (1) The prepared ferrofluid microcapsules were introduced into a phase change material container with needle-shaped heat sinks. A copper plate that could be evenly heated was installed at the bottom of the container to simulate the typical heat generation process of an electronic chip. Computational fluid dynamics (CFD) analysis was used in this part to simulate the thermal response of the system through ANSYS2023R2. The three-dimensional (3D) model of the experimental setup followed the methodology of Ali et al. and was built in SolidWorks 2022, then imported into ANSYS2023R2 Workbench to generate the mesh to ensure the accuracy of capturing the heat transfer dynamics of the system.

[0025] (2) In the simulation setting, the transient simulation method is used to capture the time and temperature changes of the system in the thermal process in real time; in the solution stage, the pressure implicit segmentation operation (PISO) method is selected as the solution strategy to ensure computational efficiency and accuracy. The finite volume method (FVM) with staggered grid arrangement is used to achieve accurate spatial discretization; the momentum and energy equations are solved using the second-order upwind format to improve accuracy, while the pressure equation uses the PRESTO! format to ensure the stability and accuracy of the pressure-velocity coupling;

[0026] (3) Based on the thermal simulation of the system, the following assumptions are made:

[0027] (3.1) During the simulation, the PCM (phase change material, contained in the phase change material container, for comparison with the OMF-HDDA microcapsules of the present application) and the OMF-HDDA microcapsules are regarded as a whole with consistent performance, and their internal components and physical properties are completely consistent;

[0028] (3.2)Assume that the fluid involved is incompressible;

[0029] (3.3) It is assumed that the molten PCM fluid exhibits laminar flow characteristics, that is, its flow pattern is smooth and orderly without turbulent interference;

[0030] (3.4)The terms related to viscous dissipation can be ignored;

[0031] (3.5) Assume that the heat transfer process does not involve radiation effects and only focus on other heat transfer modes;

[0032] (3.6) Throughout the operating range, the PCM is assumed to have uniform thermophysical properties; however, considering that the density ratio (Δρ / ρ) is less than 1, the Boussines approximation (also known as the Obebeck-Boussinesq approximation, an important method in fluid mechanics for simplifying the governing equations of buoyancy convection) is used to estimate its density; this approximation allows the influence of buoyancy in natural convection to be considered, thereby improving the simulation accuracy of the PCM behavior;

[0033] (4) Control equations: In simulating the heating and cooling of the MOSFET system, the continuity equation, energy equation, and momentum equation are considered; the following are the equations governing continuity and momentum:

[0034]

[0035] Where Sx, Sy, and Sz represent the momentum source terms in the x, y, and z directions, respectively, and are applicable to the convective phase change process. The source term is given by the following formula:

[0036]

[0037] Wherein, u, v, w are the velocities in each direction, t is the time, ρ is the density, P is the pressure, μ is the dynamic viscosity, g is the acceleration of gravity, β is the thermal expansion coefficient, and T is the temperature. Amushy (10 in this application) 5 ) is the mushy zone constant, λ represents the liquid volume fraction, ∈ (0.001 in this application) prevents the denominator from being zero;

[0038] The energy equation is as follows:

[0039]

[0040] The specific enthalpy (H) of PCM can be expressed as the sum of sensible enthalpy (h) and latent heat (ΔH):

[0041] H=h+ΔH

[0042] The calculation formula of sensible heat enthalpy is:

[0043]

[0044] Among them, C p is the specific heat, L is the latent heat, and λ is the liquid fraction. k represents the thermal conductivity of PCM, ΔH is the latent heat content, and h ref and T ref are the reference enthalpy and reference temperature respectively. The temperature dependence of the liquid fraction λ is as follows:

[0045]

[0046] This relationship reflects the significant phase change characteristics of PCM due to temperature changes during the charging and discharging process.

[0048] The present application also provides an application of the microfluidic synthesized ferrofluid microcapsules prepared as above in the field of electronic chip heat dissipation.

[0049] Advantages and beneficial effects of this application:

[0050] 1. This application uses microfluidic technology for the first time to prepare ferrofluid double emulsion microcapsules of specific components. The microcapsules use oily magnetic fluid (OMF) as the inner phase, and are subsequently encapsulated by hexanediol diacrylate (HDDA) as the intermediate oil phase; the encapsulation process is further optimized by shear force to generate a secondary emulsion; by systematically adjusting the shear rate of the external phase fluid, it is observed that the size of the OMF-HDDA microcapsules can be precisely controlled; the HDDA shell can effectively encapsulate the ferrofluid and has little effect on the thermal responsiveness of the ferrofluid, so it has effective heat transfer performance; these microcapsules can not only maintain the intrinsic functional characteristics of the core material, but also have enhanced stability and controllable performance. Compared with traditional preparation methods, the obtained microcapsules show high monodispersity and structural uniformity.

[0051] 2. This application utilizes a needle-based microfluidic device to prepare and characterize ferrofluid microcapsules; the needle device is assembled from dispensing needles of different sizes, plastic tees and cross connectors, and polypropylene accessories; these ready-made components can all be purchased online, so this easy-to-assemble needle device significantly reduces the manufacturing cost and time of microfluidic equipment; the system is specifically designed to form double emulsions through a carefully designed microchannel structure.

[0052] 3. This application rigorously validates the heat dissipation capabilities of OMF-HDDA microcapsules through simulation and experimental studies involving microfluidic chip heat dissipation; these findings highlight the potential of microfluidic technology in creating advanced packaging systems that preserve and optimize the functional properties of ferrofluids in thermal management applications.

[0053] 4. This application comprehensively characterizes the thermodynamic properties of the microcapsules and explores the effects of microcapsule size, temperature and magnetic field strength on heat dissipation efficiency; mechanical tests further prove that the microcapsules have variable stiffness characteristics, thereby improving their adaptability to dynamic environments; the photothermal effect of the OMF-HDDA microcapsules confirms that they have the ability to generate heat under alternating magnetic fields and can maintain functionality under fluctuating conditions; simulations on a microfluidic chip platform and actual heat dissipation tests on electronic chips further verify that their heat dissipation performance is superior to that of traditional coolants (such as water), especially under the action of a magnetic field; therefore, the double emulsion droplet template prepared in this application can advance the potential of microcapsule preparation technology, and can position the prepared OMF-HDDA microcapsules of this specific composition as efficient and environmentally friendly solutions for new generation thermal management applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Schematic diagram of the three-dimensional model structure of the heating system of this application.

[0055] Figure 2 A schematic structural diagram of a three-dimensional model assembly diagram of the heating system of the present application.

[0056] Figure 3 a. Needle-based microfluidic device, b. Principle of double emulsion formation.

[0057] Figure 4 Schematic diagram of the structure of the needle-based microfluidic device of the present application.

[0058] As shown in the accompanying drawings: 1. Main pipeline (for the input of inner phase), 101. First branch pipe (for the input of intermediate phase), 102. Second branch pipe (for the input of outer phase); 2. Insulating body (such as an insulating body made of rubber or other materials), 201. Receiving groove (for the microcapsules prepared by microfluidics of the present application, or other phase change materials for comparative experiments), 3. Phase change material container, 301. Needle-shaped fins, 4. Copper plate, 5. Ferrofluid microcapsules.

[0059] Figure 5a. Highly uniform spherical OMF-HDDA microcapsules; b. The generated microcapsules, with an inner diameter of di = 348.16 μm and an outer diameter of do = 406.87 μm; c. Single OMF-HDDA microcapsule; d. Microcapsules after extrusion under a scanning electron microscope (SEM); e. SEM image of OMF-HDDA microcapsules (the upper picture shows the extruded capsules, and the lower picture shows the intact capsules); fh. Elemental distribution analysis of OMF-HDDA microcapsules (C, O, and Fe element distribution); i. Overall spectrum distribution diagram.

[0060] Figure 6 a. Effect of inner phase flow rate on microcapsule size under Vm=0.01m / s, Vo=0.08m / s; b. Effect of intermediate phase flow rate on microcapsule size under Vi=0.002m / s, Vo=0.08m / s; c. Effect of outer phase flow rate on microcapsule size under Vi=0.002m / s, Vm=0.01m / s.

[0061] Figure 7 Hysteresis test results of OMF-HDDA microcapsules prepared in this application.

[0062] Figure 8 a. Weight change of OMF-HDDA microcapsules (500μm) in the presence or absence of magnetic field; b. Weight change rate of OMF-HDDA microcapsules in the presence or absence of magnetic field; c. DSC test results of OMF-HDDA microcapsules; d. Thermal conductivity of OMF-HDDA microcapsules under normal conditions; f. Thermal diffusivity of OMF-HDDA microcapsules under normal conditions; e. Thermal conductivity of OMF-HDDA microcapsules in a magnetic field environment of 0mT to 300mT; g. Thermal diffusivity of OMF-HDDA microcapsules in a magnetic field environment of 0mT to 300mT.

[0063] Fig. 9 a. Storage modulus of OMF-HDDA microcapsules under direct current (DC) magnetic field; b. Storage modulus of OMF-HDDA microcapsules under irregular alternating current (AC) magnetic field; c. Compression force that OMF-HDDA microcapsules can withstand.

[0064] Fig.10 a. OMF-HDDA microcapsules were arranged in a heart shape and placed in an alternating magnetic field coil; the thermal behavior and temperature changes of the microcapsules under the alternating magnetic field were monitored by an infrared camera; the observations were recorded at the following time points: b. immediately after the alternating magnetic field was applied (0 min); c. 5 min; d. 8 min; e. 10 min.

[0065] Fig.11a. Model verification, b. Mesh size verification, c. Time step verification of OMF-HDDA microcapsule heat dissipation simulation.

[0066] Fig.12 Thermal management capabilities of the system using four fill materials.

[0067] Fig.13 a. Construction of the microfluidic chip heat dissipation experimental device; b. Changes in the internal temperature and external temperature (surface temperature of the aluminum metal block) of the microfluidic chip during the heat dissipation process. DETAILED DESCRIPTION

[0068] The following will combine the embodiments and drawings to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only preferred embodiments, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention;

[0069] It should also be noted that: when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may be another intermediate component, fixed through the intermediate component. When a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be another intermediate component at the same time. When a component is considered to be "set on" another component, it may be directly set on the other component or there may be another intermediate component at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only; the front and rear ends of this application are the front end when the pen tip is extended in the use state, and the rear end where the pressing part is located. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0070] As attached Figure 3-4As shown, it is a related drawing of the microfluidic system used in the preparation of microcapsules in the present application. The device of the microfluidic system includes a main pipeline 1, and the main pipeline 1 is also provided with a first branch pipe 101 and a second branch pipe 102; one end of the main pipeline 1 is a feed end, and the other end is a discharge end, and the feed end is used for the input of the inner phase; the first branch pipe 101 is symmetrically arranged along the radial direction of the main pipeline 1, and both are used for the input of the outer phase; the second branch pipe 102 is symmetrically arranged along the radial direction of the main pipeline, and both are used for the input of the intermediate oil phase; wherein the first branch pipe 101 and the second branch pipe 102 are connected sequentially along the direction from the feed end to the discharge end of the main pipeline 1.

[0071] The above-mentioned main pipeline of the present application can be composed of a syringe tube structure of a composite microfluidic size, wherein the first branch tube 101 and the second branch tube 102 are structures integrally formed with the main pipeline 1 or are assembled and assembled, and a three-way structure (one first branch tube, a feed direction port of the main pipeline, and an outflow direction end of the main pipeline) is formed at the position of the first branch tube 101, and a four-way structure (two second branches, a flow direction port of the main pipeline, and a flow direction port of the main pipeline) is formed at the position of the second branch tube 102; materials of each phase can be pumped into the microfluidic system through a syringe pump; specifically, the microfluidic system of the present application can be assembled using a distribution needle, a plastic tee (constituting a three-way structure) and a cross connector (constituting a four-way structure) and polypropylene accessories; since these ready-made components can be purchased online, the easy-to-assemble needle device significantly reduces the manufacturing cost and time of the microfluidic equipment.

[0072] The above-mentioned microfluidic system is used to prepare the OMF-HDDA microcapsules of this application:

[0073] (1) First, prepare the oil-based ferrofluid Fe 3 O 4 The internal phase is composed of 1,6-hexanediol diacrylate (HDDA) and the intermediate oil phase is added with polyvinyl alcohol (PVA) and F108's foreign minister;

[0074] (2) A needle-based microfluidic multiphase flow system is used, the system includes a main pipeline, the main pipeline 1 is also provided with a first branch pipe 101 and a second branch pipe 102; one end of the main pipeline is a feed end, and the other end is a discharge end, the feed end is used for inputting the inner phase; two first branch pipes 101 are symmetrically arranged along the radial direction of the main pipeline 1, both for inputting the outer phase; two second branch pipes 102 are symmetrically arranged along the radial direction of the main pipeline 1, both for inputting the intermediate oil phase; the inner phase, the intermediate oil phase and the outer phase prepared in step (1) are respectively inputted from the corresponding ports of the needle-based microfluidic multiphase flow system, and then the three-phase material finally flows out from the discharge end of the main pipeline;

[0075] The feeding sequence is first the external phase, then the middle phase, and finally the internal phase. The interval between feeding each phase is controlled at about 1 min, so that a more ideal OMF-HDDA microcapsule structure can be obtained.

[0076] (3) During the output process of the main pipeline, the OMF-HDDA microcapsules are cured under ultraviolet (UV) irradiation to obtain OMF-HDDA microcapsules.

[0077] 1. Materials, Experiments, and Methods

[0078] 1.1. Materials: In the oil-in-oil-in-water (O / O / W) double emulsion microfluidic system, the inner phase is composed of an oil-based ferrofluid Fe 3 O 4 The composition was purchased from Jiangxi Kede Magnetic Materials Technology Co., Ltd. (Jiangxi, China). The shell material of the intermediate oil phase was 1,6-hexanediol diacrylate (HDDA, Sigma-Aldrich Co., Ltd.), which was selected for its excellent mechanical strength and chemical stability. HDDA formed a solid intermediate layer in the microfluidic system, which effectively protected the inner phase and ensured the overall stability of the double emulsion. The outer phase was an aqueous phase, which required the addition of polyvinyl alcohol (PVA, molecular weight 13,000–23,000, degree of hydrolysis 87–89%, Sigma-Aldrich Co., Ltd.) and F108 (Sigma-Aldrich Co., Ltd.) to maintain stability. Specifically, the mass percentage of PVA in the aqueous phase is 8%, because of its excellent adhesion and film-forming properties in aqueous solution, it can effectively prevent the mutual penetration between the inner phase and the outer phase; in addition, The mass percentage of F108 in the aqueous phase is 2%, which is a non-ionic surfactant also provided by Sigma-Aldrich, and can further improve the stability of the external phase and prevent the aggregation and sedimentation of the internal phase. These ingredients together ensure the long-term stable operation of the double emulsion microfluidic system; the specific preparation process is to use the above-mentioned microfluidic system to prepare the OMF-HDDA microcapsules of this application.

[0079] 1.2. Characterization:

[0080] 1.21. Morphology measurement: The morphology of OMF-HDDA microcapsules was observed by high-resolution optical microscopy (Ningbo Yongxin Optics Co., Ltd., China) equipped with 10X, 20X and 40X objective lenses. In order to comprehensively and in detail analyze the morphological characteristics, observations were carried out at different magnifications, thereby conducting a multi-scale in-depth evaluation of the structural properties of the microcapsules. In addition, the microscopic morphology of the microcapsules was further observed using a scanning electron microscope (SEM, FEG 250, FEIQuanta, USA), confirming the successful encapsulation of HDDA as the shell material.

[0081] 1.22. Magnetic property measurement: The hysteresis properties of OMF-HDDA microcapsules were characterized by a physical property measurement system (PPMS, DynaCool, Quantum Design, USA).

[0082] 1.23. Thermal properties measurement: The thermal transition characteristics of OMF-HDDA microcapsules were analyzed by differential scanning calorimetry (DSC214, NETZSCH, Germany). During the test, the temperature range of the microcapsule samples was set from -100°C to 300°C to fully cover all possible thermal transition intervals. In addition, the thermal decomposition behavior of OMF-HDDA microcapsules was studied using a thermogravimetric analyzer (TGA, TG209F1, NETZSCH, Germany). The test temperature range of the sample was set from 0°C to 800°C to fully capture all potential thermal transitions and decomposition processes. In order to prevent oxidation or decomposition of the sample during heating, the entire test was carried out in a nitrogen atmosphere with a constant nitrogen flow rate to ensure a stable inert environment. In order to ensure the reliability and repeatability of the data, all experiments were repeated multiple times and rigorous statistical analysis was performed. In addition, the thermal conductivity and thermal diffusivity of the microcapsules were measured by a thermal constant tester (Hotdisk, KAITS, Sweden).

[0083] 1.24. Mechanical property measurements: The stiffness properties of ferrofluids show significant variability under the influence of an applied magnetic field. The changes in the stiffness properties of OMF-HDDA microcapsules under different magnetic field strengths were systematically studied using a magnetorheometer (DHR-2, TA Corporation, USA). The microcapsules were tested under controlled magnetic field conditions to systematically evaluate the changes in their stiffness properties. This method enables precise evaluation of the magnetic response behavior of the microcapsules and provides important insights into the dynamic interaction between magnetic field strength and material stiffness.

[0084] 1.3. Simulation method:

[0085] 1.31. Simulation setup: To evaluate the applicability of OMF-HDDA in thermal management of electronic devices, OMF-HDDA is introduced into a phase change material container with pin-shaped heat sinks; specifically, Figure 1-2 As shown: the simulation system includes an insulating body 2, wherein a receiving groove 201 for receiving a phase change material container 3 is provided in the insulating body 2, wherein the phase change material container 3 is placed in the receiving groove 201, wherein a copper plate 4 is provided between the receiving groove 201 and the phase change material container 3, wherein a plurality of needle-shaped fins 301 extending in the thickness direction are provided in the phase change material container 3, wherein a ferromagnetic fluid microcapsule 5 is contained in the phase change material container 3, wherein the ferromagnetic fluid microcapsule 5 covers the needle-shaped fins 301. A copper plate 4 capable of uniform heating is installed at the bottom of the phase change material container 3 of the present application to simulate the typical heat generation process of an electronic chip. This part adopts computational fluid dynamics (CFD) analysis to simulate the thermal response of the system through ANSYS2023R2. The three-dimensional (3D) model of the experimental device follows the methodology of Ali et al., is constructed in SolidWorks 2022, and then imported into ANSYS2023R2Workbench to generate a mesh to ensure the accuracy of capturing the heat transfer dynamics of the system. Table S1 summarizes the solid materials that make up the system (the preparation material of the phase change material container, 6061Al is used in this example), and Table S2 lists the thermophysical properties of the four filling materials used for comparative analysis. In the simulation setting, the transient simulation method is used to capture the time-temperature changes in the thermal process of the system in real time. In the solution stage, the pressure implicit partitioning operation (PISO) method is selected as the solution strategy to ensure computational efficiency and accuracy. The finite volume method (FVM) with staggered grid arrangement is used to achieve accurate spatial discretization. The momentum and energy equations are solved using the second-order upwind format to improve accuracy, while the pressure equation uses the PRESTO! format to ensure the stability and accuracy of the pressure-velocity coupling.

[0086] Table S1 Preparation materials of phase change material container

[0087]

[0088]

[0089] Table S2 Four phase change materials

[0090]

[0091] Based on the thermal simulation of the system, the following assumptions are made: (1) During the simulation, PCM (phase change material) and OMF-HDDA microcapsules are regarded as a whole with consistent properties, and their internal composition and physical properties are completely consistent. (2) The fluid involved is assumed to be an incompressible fluid. (3) It is assumed that the molten PCM fluid exhibits laminar characteristics, that is, its flow pattern is smooth and orderly, without turbulent interference. (4) The terms related to viscous dissipation can be ignored. (5) It is assumed that the heat transfer process does not involve radiation effects, and only other heat transfer modes are concerned. (6) Within the entire operating range, it is assumed that PCM has uniform thermophysical properties. However, considering that the density ratio (Δρ / ρ) is less than 1, the Boussines approximation is used to estimate its density. This approximation allows the influence of buoyancy in natural convection to be considered, thereby improving the simulation accuracy of PCM behavior.

[0092] 1.32. Control equations: In simulating the heating and cooling of the MOSFET system, the continuity equation, energy equation, and momentum equation are considered. The following are the equations that control continuity and momentum:

[0093]

[0094] Where Sx, Sy, and Sz represent the momentum source terms in the x, y, and z directions, respectively, and are applicable to the convective phase change process. The source term is given by the following formula:

[0095]

[0096] Among them, u, v, w are the velocities in each direction, t is the time, ρ is the density, P is the pressure, μ is the dynamic viscosity, g is the gravitational acceleration, β is the thermal expansion coefficient, and T is the temperature. Amushy (10 in this study) 5 ) is the mushy zone constant, λ represents the liquid volume fraction, and ∈ (0.001 in this study) prevents the denominator from being zero.

[0097] The energy equation is as follows:

[0098]

[0099] The specific enthalpy (H) of PCM can be expressed as the sum of sensible enthalpy (h) and latent heat (ΔH):

[0100] H=h+ΔH

[0101] The calculation formula of sensible heat enthalpy is:

[0102]

[0103] Among them, C p is the specific heat, L is the latent heat, and λ is the liquid fraction. k represents the thermal conductivity of PCM, ΔH is the latent heat content, and h refand T ref are the reference enthalpy and reference temperature respectively. The temperature dependence of the liquid fraction λ is as follows:

[0104]

[0105] This relationship reflects the significant phase change characteristics of PCM due to temperature changes during the charging and discharging process.

[0107] 2. Results and Discussion

[0108] 2.1. Preparation of OMF-HDDA microcapsules

[0109] Specifically, according to Figure 3 The needle-based microfluidic multiphase flow system shown in a, the blue needle is connected to the inner phase OMF, the three-way tube is connected to HDDA, and the four-way tube is connected to the PVA aqueous solution. This experimental device successfully prepared double emulsion droplets ( Figure 3 b), and rapidly cured under ultraviolet (UV) irradiation (UV wavelength is 365 nm); the rapid curing process effectively maintains the structural integrity and functional properties of the obtained OMF-HDDA microcapsules; Figure 5 As shown in a, OMF-HDDA microcapsules showed high monodispersity, and the coefficient of variation (CV) was less than 5%, which was calculated as follows:

[0110]

[0111] Among them, CV is a statistical indicator that measures the relative variability of size, defined as the ratio of the standard deviation (σ) to the mean (μ); studies have shown that a highly uniform size distribution helps maintain consistent performance in a variety of applications; Figure 5 Microscope images of b and Figure 5 c shows that the minimum particle size of the generated microcapsules is 406.87 μm and the core size is 348.16 μm. These results demonstrate the effectiveness of this configuration in achieving precise size control to meet specific application requirements. In addition, the surface morphology of the OMF-HDDA microcapsules is shown in Figure 5 As shown in d; Figure 5 The elemental composition of the microcapsules shown in e was further verified by energy dispersive X-ray spectroscopy (EDS) analysis (see Figure 5 f–h); This analysis provided a detailed characterization of the elemental distribution of the OMF-HDDA microcapsules, which was critical to confirm their encapsulation success and structural integrity of the intended composition; Figure 5As shown, where a. highly uniform spherical OMF-HDDA microcapsules; b. generated microcapsules with inner diameter di = 348.16 μm and outer diameter do = 406.87 μm; c. single OMF-HDDA microcapsule; d. microcapsules after being squeezed under a scanning electron microscope (SEM); e. SEM image of OMF-HDDA microcapsules (the upper picture shows the squeezed capsules, and the lower picture shows the intact intact capsules); fh. elemental distribution analysis of OMF-HDDA microcapsules (C, O, Fe element distribution); i. overall spectrum distribution diagram.

[0112] 2.2 Effect of three-phase flow rate on the size of OMF-HDDA microcapsules:

[0113] Empirical studies and theoretical analysis have shown that the phase flow rate is a key factor affecting the morphological characteristics of double emulsion droplets. According to the following formulas 2 to 4, the flow rate of each phase (respectively denoted as Vi (inner), Vm (middle) and Vo (outer)) is derived from the volume flow rate (Qi, Qm and Qo) involved in the microfluidic system and the diameter of the needle:

[0114]

[0115] Among them, Di1 and Di2 represent the inner diameter and outer diameter of the main channel, i.e. the inner needle, respectively; Dm1 and Dm2 represent the inner diameter and outer diameter of the first branch, i.e. the intermediate phase needle, respectively; Do1 represents the inner diameter of the second branch, i.e. the outer phase needle; these parameters are crucial in determining the fluid dynamics behavior during microfluidic packaging; here Di1 = 0.39 mm, Di2 = 0.63 mm, Dm1 = 1 mm, Dm2 = 1.3 mm, Do1 = 1.5 mm.

[0116] Specifically, the physical properties (including density, viscosity and interfacial tension) between the two phases of the present application and the specified flow parameters of each phase are summarized in Table 1:

[0117] Table 1. Fluid properties and setting parameters in double emulsion experiments

[0118]

[0119] 2.21. Effect of internal phase flow rate

[0120] When the flow rate of the inner phase liquid is low, the middle phase liquid will exert excessive pressure, thereby inhibiting the flow of the inner phase liquid; this inhibition will prevent the inner phase liquid from flowing out of the specified needle tube, which may lead to the formation of single emulsion particles composed only of the middle phase liquid; on the contrary, when the flow rate of the inner phase liquid is high, the inner phase liquid will quickly escape from the needle tube, resulting in uneven coating of the OMF-HDDA microcapsules and may even cause capsule rupture; specifically, if Figure 6As shown in Figure a, an increase in the internal phase flow rate Vi will cause more internal phase liquid to be injected into the inner droplet, thereby increasing the diameter di of the inner droplet; this increase not only affects the overall size of the capsule, but may also affect the stability and uniformity of the capsule.

[0121] 2.22. Effect of interphase flow rate

[0122] Except for the flow rate of the intermediate phase fluid, the other parameters were kept constant to evaluate their effects on the particle size and shell thickness of the OMF-HDDA microcapsules; Figure 6 As shown in figure (b), when the intermediate phase flow rate Vm increases from 0.006 m / s to 0.01 m / s, the outer droplet diameter do increases significantly, while the inner droplet diameter di decreases accordingly; this phenomenon can be attributed to the increased shear force exerted by the increase in the intermediate phase flow rate, which compresses the inner fluid, thereby causing di to decrease; at the same time, during the extrusion process, a larger volume of the intermediate phase fluid is introduced into the outer droplet, resulting in an increase in do; this differentiated mechanism causes do and di to show opposite trends of change, ultimately increasing the shell thickness of the OMF-HDDA microcapsules.

[0123] 2.23. Effect of external phase flow rate

[0124] During the analysis, it was observed that the droplet morphology showed a consistent change trend when the external phase flow rate Vo increased, while other parameters remained unchanged (such as Figure 6 c); Specifically, for OMF-HDDA microcapsules, both the outer droplet diameter do and the inner droplet diameter di show a decreasing trend, which can be theoretically explained by the following linear relationship:

[0125] F σ =μ o V o d o Formula (5)

[0126] Among them, μo is the viscosity of the external phase liquid, Vo is the flow rate of the external phase liquid, do is the diameter of the external droplet, Fσ is the force term, and σ is the surface tension; when the droplet breaks near the outlet, the shear stress on the outer surface of the droplet increases significantly with the increase of Vo; this increase in shear stress accelerates the formation of the droplet, resulting in a decrease in do and di; at the same time, the droplet shell thickness fluctuates in this process, showing up and down fluctuations; these fluctuations are mainly due to transient instabilities caused by changes in force at different flow rates during the droplet formation process, which in turn leads to fluctuations in the relative shell thickness value. This phenomenon emphasizes the importance of precise control of the external phase flow rate in controlling the size and shell thickness of the microcapsule; further analysis shows that with the increase of Vo, the shear stress of the droplet during the formation process gradually increases, promoting the formation of smaller droplets; in this process, the surface tension effect is also enhanced, further promoting the reduction of the droplet size; this result shows that by regulating the external phase flow rate, the morphological characteristics of the microcapsules can be effectively adjusted to meet specific application requirements.

[0127] Specifically, Figure 6 As shown in the figure, a. The effect of the inner phase flow rate on the size of the microcapsules under the conditions of Vm = 15uL / min, Vo = 1000uL / min. b. The effect of the middle phase flow rate on the size of the microcapsules under the conditions of Vi = 5uL / min, Vo = 1000uL / min. c. The effect of the outer phase flow rate on the size of the microcapsules under the conditions of Vi = 5uL / min, Vm = 15uL / min.

[0128] 2.3 Magnetic properties of OMF-HDDA microcapsules

[0129] A notable property of ferrofluids is their ability to respond to magnetic fields. After encapsulating the ferrofluid in HDDA, its magnetization properties are maintained, allowing the magnetic nanoparticles to align according to the direction of the external magnetic field. Under the action of a 5mT magnetic field, the OMF-HDDA microcapsules showed significant mobility. In addition, the magnetic properties of the microcapsules were analyzed by hysteresis tests, showing their magnetization intensity ( Figure 7 ); This magnetic responsiveness indicates that the microcapsule contains a sufficient concentration of magnetic components to enable it to move effectively under an external magnetic field. This property is crucial for achieving precise positioning and control of microcapsules in complex environments; by adjusting the strength and direction of the magnetic field, the movement trajectory of the microcapsule can be precisely controlled, laying the foundation for innovative applications in microfluidic systems, biomedical engineering, smart materials and other cutting-edge fields.

[0130] 2.4 Thermal properties of OMF-HDDA microcapsules

[0131] Considering the efficient heat dissipation performance of ferrofluid, the thermodynamic properties of OMF-HDDA microcapsules were tested in detail. Under the action of 300mT DC frequency magnetic field, the thermogravimetric loss of the microcapsules showed almost complete decomposition ( Figure 8 a). The rate of change of thermogravimetric loss is comparable to that under normal conditions ( Figure 8 b), indicating that the magnetic field has no significant effect on the thermal decomposition process of the microcapsules. Differential scanning calorimetry (DSC) analysis results show that OMF-HDDA microcapsules exhibit good stability in a wide temperature range of 0-150°C ( Figure 8 c). This property ensures that the microcapsules can maintain consistent performance and reliability in various thermal management applications. Specifically, the stability of the microcapsules allows them to maintain their structure and function in high-temperature and variable-temperature environments without being susceptible to thermal degradation or performance degradation. The excellent thermodynamic properties of OMF-HDDA microcapsules in microchannels significantly improve the heat dissipation effect. Experimental results show that the microcapsules can effectively transfer heat from high-temperature areas to low-temperature areas, thereby ensuring temperature balance throughout the system. This property makes it an ideal heat dissipation functional material, especially suitable for use as a coolant.

[0132] Using needle-based microfluidic technology, OMF-HDDA microcapsules with different diameters (400 μm, 500 μm, and 600 μm) were successfully synthesized. Figure 8 d and Figure 8 f shows that the thermal conductivity and thermal diffusivity of the microcapsules are positively correlated with their size. The interfacial thermal resistance plays a key role in the effect of thermal conductivity on the microcapsule interface. In smaller microcapsules, the interfacial thermal resistance effect is enhanced due to the increase in specific surface area, thereby reducing the overall thermal conductivity. In contrast, as the size of the microcapsules increases, the specific surface area decreases, the effect of the interfacial thermal resistance weakens, and the thermal conductivity is improved. In addition, the shell thickness does not scale with the size of the microcapsules; larger microcapsules exhibit relatively thin shells, which further reduces the thermal resistance contribution of the shell. In addition, in larger microcapsules, the effective volume fraction of the MRF increases, making the overall thermal conductivity closer to the thermal conductivity of the MRF itself. Larger microcapsules also promote more efficient thermal contact between particles and promote the formation of a continuous heat transfer network composed of magnetic particles, thereby significantly improving the thermal conductivity. In summary, the phenomenon of increased thermal conductivity due to increased microcapsule size can be attributed to the reduction of interfacial thermal resistance, the reduction of relative shell thickness, and the enhancement of heat transfer paths inside the MRF. Figure 8 f shows that in the absence of a magnetic field, Fe 3 O 4 The nanoparticles are randomly dispersed in the carrier liquid, and their distribution remains stable when the temperature changes. This indicates that temperature fluctuations have little effect on the microstructure and heat transfer path inside the microcapsules. 3 O 4The nanoparticles are dispersed in a low thermal conductivity carrier fluid and fail to form a strong heat conduction network, so the heat transfer within the system relies mainly on the thermal conduction mechanism rather than convection or radiation. The thermal conduction path mainly consists of direct contact between the particles, the carrier fluid, and the shell material. Since temperature changes do not usually significantly change these contact conditions, the overall effect on thermal conductivity is negligible. In addition, Fe 3 O 4 The thermal conductivity of nanoparticles is inherently very stable, varying by less than 5% over the typical operating temperature range.

[0133] When the diameter of OMF-HDDA microcapsules is fixed at 500 μm, the thermal conductivity and thermal diffusivity increase significantly as the magnetic field strength increases from 0 mT to 300 mT ( Figure 8 e) This improvement is attributed to the Fe 3 O 4 Rearrangement of nanoparticles under the action of a magnetic field. The initially randomly distributed particles gradually align along the direction of the magnetic field to form an ordered chain or network structure. This ordered configuration effectively shortens the heat transfer path and improves the efficiency of direct heat transfer between particles, thereby significantly improving the overall thermal conductivity of the microcapsules. At higher magnetic field intensities, the magnetic interaction between particles is enhanced, leading to a tighter bond and the formation of a more continuous heat conduction network. This continuity minimizes the interfacial thermal resistance during heat conduction, further improving thermal conductivity and thermal diffusivity. In addition, the increase in magnetic field intensity synergistically improves the heat transfer efficiency through the possible local microconvection effect, thereby enhancing the heat transfer path within the microcapsules. It is worth noting that even at different magnetic field intensities, the effect of temperature on the thermal properties of microcapsules remains small ( Figure 8 g). This is because the Fe 3 O 4 The particle chain structure has high stability, and temperature changes do not significantly change its structure. This causes the heat transfer path within the microcapsule to remain relatively stable, so that the thermal conductivity and thermal diffusivity hardly fluctuate over a large temperature range. This intrinsic stability highlights the applicability of ferrofluid microcapsules as thermal management materials in environments with large temperature fluctuations, especially in application scenarios that require stable thermal performance.

[0134] Specifically, Figure 8a. Weight change of OMF-HDDA microcapsules (500μm) in the presence and absence of magnetic field. b. Weight change rate of OMF-HDDA microcapsules in the presence and absence of magnetic field. c. DSC test results of OMF-HDDA microcapsules. d. Thermal conductivity of OMF-HDDA microcapsules under normal conditions. f. Thermal diffusivity of OMF-HDDA microcapsules under normal conditions. e. Thermal conductivity of OMF-HDDA microcapsules in a magnetic field environment of 0mT to 300mT. g. Thermal diffusivity of OMF-HDDA microcapsules in a magnetic field environment of 0mT to 300mT.

[0135] As shown in the comparative data in Table 2, the thermal conductivity of OMF-HDDA microcapsules is superior to that of other formulations. Although the size of microcapsules synthesized by microfluidic technology is relatively large, this method has significant advantages in encapsulation efficiency and particle uniformity. It is worth noting that the encapsulation rate of OMF-HDDA microcapsules reached 100%, ensuring that the ferrofluid is completely encapsulated by the protective shell. In addition, the microfluidic process achieves a high degree of monodispersity and a uniform distribution of microcapsule sizes. These characteristics highlight the high efficiency of microfluidic synthesis technology in producing high-quality microcapsules with excellent thermal performance, making it particularly suitable for application scenarios with precise control requirements for particle properties and consistent thermal management capabilities.

[0136] Table 2. Comparison of performance between conventional magnetic microcapsules and OMF-HDDA microcapsules

[0137]

[0138]

[0139] 2.5 Mechanical properties of OMF-HDDA microcapsules

[0140] Ferrofluids are highly responsive to external pressure fluctuations, especially in microscale applications, where pressure changes directly affect particle arrangement and magnetic properties. Shear modulus analysis shows that the stiffness of OMF-HDDA microcapsules under shear stress remains in a stable range of about 3 to 4×10 -3 MPa( Fig. 9 a), reflecting its stable mechanical properties under shear stress. However, under strong magnetic fields, the stiffness of these microcapsules increased significantly; in particular, in a 500mT direct current (DC) magnetic field, the stiffness was about 1MPa, which is about a thousand times higher than that in the absence of a magnetic field. When the microcapsules were in an alternating current (AC) magnetic field in the form of a sinusoidal function, their modulus changed accordingly, further confirming that the mechanical properties of the microcapsules would adjust with magnetic stimulation ( Fig. 9 b).

[0141] Furthermore, the vertical compression tests further revealed the mechanical robustness of the microcapsules. These tests showed that as the compression distance decreased, the microcapsules were able to withstand an applied force of approximately 2.75 N before significant deformation occurred ( Fig. 9 c), indicating that the microcapsules have sufficient mechanical strength to resist compressive forces without immediate structural damage. This property is particularly important in applications that may be subjected to external mechanical forces, as it ensures that the microcapsules can maintain their structural integrity and functional performance over long periods of use; specifically, Fig. 9 a. Storage modulus of OMF-HDDA microcapsules under direct current (DC) magnetic fields. b. Storage modulus of OMF-HDDA microcapsules under irregular alternating current (AC) magnetic fields; c. Compressive force that OMF-HDDA microcapsules can withstand.

[0142] 2.6 Applications of OMF-HDDA Microcapsules

[0143] 2.61. Photothermal Imaging

[0144] Under specific conditions, magnetic nanoparticles in ferrofluids can respond to light of a specified wavelength through functionalization. The magnetic nanoparticles embedded in OMF-HDDA microcapsules exhibit a photothermal effect, i.e., they can absorb the energy of an alternating magnetic field and convert it into heat, thereby changing the local temperature and fluid response characteristics. In this application, the prepared microcapsules were arranged in a heart-shaped pattern and placed inside a coil capable of generating an alternating magnetic field ( Fig.10 a). Due to the presence of iron oxide (Fe 3 O 4 ) nanoparticles, the temperature inside the coil gradually increased from the ambient temperature to approximately 40 °C. As shown in Fig.10 b to Fig.10 e, the brightness intensity at the heart-shaped position gradually increased, indicating that the OMF-HDDA microcapsules functioned as the main heat source; specifically, Fig.10 a. OMF-HDDA microcapsules were arranged in a heart shape and placed in an alternating magnetic field coil. The thermal behavior and temperature changes of the microcapsules under the action of the alternating magnetic field were monitored by an infrared camera. Observations were recorded at the following time points: b. Immediately after the alternating magnetic field was applied (0 minutes); c. 5 minutes; d. 8 minutes; e. 10 minutes.

[0145] 2.62. Verification of the heat dissipation simulation model of OMF-HDDA microcapsules: To verify the simulation process, the study by Ali et al. was replicated and its results were compared with the current simulation results, as shown in Fig.11 a. The figure shows the differences between the experimental data of Ali et al. and the simulation results of this application; Fig.11The temperature distribution curve in a shows that the two sets of data are highly consistent, with the maximum deviation of the temperature measurement being less than 4%. This high degree of consistency verifies the accuracy of the ANSYS simulation process, thereby confirming the applicability of the model in analyzing the thermal behavior of systems containing OMF-HDDA.

[0146] Mesh size verification: Before numerical simulation of the system, the mesh size and time step were verified to improve the simulation accuracy. For mesh size verification, three mesh sizes (4 mm to 6 mm, see Table S3 for details) were discretized and analyzed through comparative simulation. Fig.11 As shown in Figure 2b, the profile of the 5 mm mesh is highly consistent with that of the 4 mm mesh, indicating that the two are comparable in accuracy. Although a finer mesh size can theoretically improve simulation accuracy, choosing a 5 mm mesh size can achieve the best balance between accuracy and computational efficiency. Therefore, the 5 mm mesh was selected as the standard mesh size for all subsequent simulations.

[0147] Table S3 Various grid sizes.

[0148]

[0149] Time step verification: After completing the grid size verification, the time step verification was performed to determine the optimal time step for the simulation. Based on the verified grid size, four time steps (0.1 to 0.5 minutes) were simulated and analyzed. Fig.11 c, 0.25 minutes is selected as the time step because it reduces the computational cost while maintaining the accuracy of the simulation results. Comparison of material simulation performance: Under the condition of ambient temperature of 25°C, the system filled with four different materials was heated for 90 minutes, and the average temperature distribution is shown in Fig.12As shown. Throughout the simulation, the water-filled system showed a uniform temperature rise, eventually reaching 55.43°C, the highest temperature among the four systems. As a phase change material (PCM), RT-35HC did not undergo a phase change initially because its starting temperature was 25°C below its melting point, so its ability to suppress the system temperature in the initial stage was limited, resulting in a rapid temperature rise. About 12 minutes into the simulation, RT-35HC entered a solid-liquid mixed state through a phase change, absorbing a large amount of latent heat of fusion, effectively slowing down the temperature rise of the system. This phase change process ended at about 70 minutes into the simulation. Subsequently, due to the completion of the phase change, RT-35HC could not absorb any further heat, resulting in a rapid temperature rise, eventually reaching about 45°C at the end of the simulation. According to the simulation results, the filling material containing OMF-HDDA microcapsules exhibited superior thermal management capabilities compared to the first two materials. Due to the lack of a phase change range, the OMF-HDDA microcapsule filling material provided continuous and effective thermal regulation capabilities throughout the heating simulation. In addition, after magnetizing these microcapsules (magnetic field strength of 300mT), their thermal conductivity was significantly enhanced, allowing the system to maintain the lowest average temperature throughout the simulation, ultimately reaching 35°C. This temperature is 36.86% lower than that of the water-filled system, highlighting the excellent performance of magnetized OMF-HDDA microcapsules in thermal management applications. In addition, since the OMF-HDDA microcapsules filled in this simulation are static, their excellent thermal conductivity performance has not been fully reflected. Therefore, subsequent dynamic experiments will more intuitively demonstrate the excellent thermal performance of OMF-HDDA microcapsules under magnetic field excitation.

[0150] 2.63. Chip heat dissipation performance of OMF-HDDA microcapsules

[0151] In order to explore the differences in the thermophysical properties of OMF-HDDA under different magnetic field intensities, a Fig.13 The small channel liquid cooling platform shown in a. At the beginning of the experiment, OMF-HDDA was dissolved in deionized water to prepare a solution with a mass fraction of 0.5%, and was placed in a beaker, and its temperature was maintained at 25°C using a water bath in a constant temperature water tank. The chip was simulated by two electric heaters, each with a power of 12W, placed under an aluminum metal block with a wavy channel. A peristaltic pump was used to circulate the OMF-HDDA solution through the wavy channel at a flow rate of 50ml / min.

[0152] Magnets of varying strengths (from 0 to 300 mT) were placed on top of the aluminum block. The magnetic field strength applied in this experiment is not expected to have an effect on the chip capacitance. In addition, the temperature inside the microchannel as well as the external temperature were measured using a K-type thermocouple. Specifically, the external temperature measurement corresponds to the temperature of the top surface of the aluminum block.

[0153] like Fig.13As shown in Figure b, under standard conditions, the cooling efficiency of adding OMF-HDDA microcapsules is better than that of using water alone. During the experiment, magnetic fields of different strengths (0mT to 300mT) were applied around the chip, and the results showed that the cooling effect was significantly enhanced with the increase in magnetic field strength. This highlights the efficient heat dissipation performance of OMF-HDDA microcapsules under the action of magnetic fields ( Fig.13 b).

[0154] The following conclusions were obtained through the above examples, comparative examples and simulation methods: 1. High monodispersity: OMF-HDDA microcapsules showed excellent uniformity, and its coefficient of variation was significantly lower than 5%; 2. Dynamic change of shell thickness: The experimental results show that the flow rate of the inner and outer phases has no significant effect on the shell thickness, while the flow rate of the intermediate phase is positively correlated with the shell thickness; 3. Magnetic properties: The microcapsules show effective movement under magnetic traction, reflecting their soft magnetic properties; 4. Thermal conductivity: The size of the microcapsules is positively correlated with the thermal conductivity, and the thermal conductivity is further enhanced under a stronger magnetic field. Temperature changes have little effect on it; 5. Photothermal function: The iron oxide nanoparticles in the core of the microcapsule still maintain efficient heat generation under the action of an alternating magnetic field; 6. Heat dissipation and cooling performance: Simulation and experimental evaluation confirm that OMF-HDDA microcapsules perform well in electronic chip heat dissipation and microchannel cooling applications, making them potential candidates for advanced coolants and thermal management materials. The above test results show that the OMF-HDDA microcapsules prepared in this application have broad application prospects in magnetic response and thermal management systems, showing significant industrial application potential.

Claims

1. A microfluidic synthesized ferrofluid microcapsule, characterized in that: The raw materials for preparing the microcapsule include an inner phase, an intermediate oil phase and an outer phase. The inner phase is composed of oil-based ferromagnetic fluid Fe3O4, the intermediate oil phase is 1,6-hexanediol diacrylate, and the outer phase is a mixture of polyvinyl alcohol and The aqueous phase of F108.

2. The microfluidic synthesized ferrofluid microcapsule according to claim 1, characterized in that: The oil-based ferromagnetic fluid Fe3O4 mainly comprises Fe3O4 nanoparticles, silicone oil and a stabilizer; the molecular weight of the polyvinyl alcohol is 13,000-23,000, and the degree of hydrolysis is 87-89%.

3. The microfluidic synthesized ferrofluid microcapsule according to claim 1, characterized in that: The mass percentage of the polyvinyl alcohol in the water phase is 5-10%. The mass percentage of F108 in the water phase is 1-3%.

4. The microfluidic synthesized ferrofluid microcapsule according to claim 1, characterized in that: The flow rate of the inner phase is 5-15uL / min; the flow rate of the intermediate oil phase is 10-20uL / min; and the flow rate of the outer phase is 900-1200uL / min.

5. A method for preparing the microfluidic synthesized ferrofluid microcapsules according to any one of claims 1 to 4, characterized in that: include: (1) First, an inner phase composed of an oil-based ferromagnetic fluid Fe3O4, an intermediate oil phase composed of 1,6-hexanediol diacrylate, and a phase containing polyvinyl alcohol and F108's foreign minister; (2) A needle-based microfluidic multiphase flow system is used, the system comprises a main pipeline, the main pipeline is further provided with a first branch pipe and a second branch pipe; one end of the main pipeline is a feed end, and the other end is a discharge end, the feed end is used for inputting the inner phase; at least one first branch pipe is provided along the radial direction of the main pipeline, for inputting the intermediate oil phase; two second branch pipes are symmetrically provided along the radial direction of the main pipeline, both for inputting the outer phase; the inner phase, the intermediate oil phase and the outer phase prepared in step (1) are respectively inputted from the corresponding ports of the needle-based microfluidic multiphase flow system, and then the three-phase material finally flows out from the discharge end of the main pipeline; (3) During the output process of the main pipeline, the OMF-HDDA microcapsules are cured under ultraviolet light to obtain.

6. The method for preparing microfluidic synthesized ferrofluid microcapsules according to claim 5, characterized in that: The first branch pipe and the second branch pipe are arranged in sequence from the feed end to the discharge end of the main pipeline.

7. The method for preparing microfluidic synthesized ferrofluid microcapsules according to claim 5, characterized in that: The wavelength of the ultraviolet light used for curing is 365 mm; the diameter of the OMF-HDDA microcapsule is 400-600 μm.

8. A heating system for the ferrofluid microcapsules synthesized by microfluidics according to any one of claims 1 to 4, characterized in that: The system includes an insulating body, wherein a receiving groove for receiving a phase change material container is arranged in the insulating body, the phase change material container is placed in the receiving groove, a copper plate is arranged between the receiving groove and the phase change material container, a plurality of needle-shaped fins extending along the thickness direction are arranged in the phase change material container, ferromagnetic fluid microcapsules are contained in the phase change material container, and the ferromagnetic fluid microcapsules cover the needle-shaped fins.

9. A method for thermal simulation using the heating system of claim 8, characterized in that: include: (1) introducing the prepared ferrofluid microcapsules into a phase change material container with needle-shaped heat sinks; A copper plate that can be heated evenly is installed at the bottom of the container to simulate the typical heat generation process of electronic chips. This part uses computational fluid dynamics analysis to simulate the thermal response of the system through ANSYS2023R2. The 3D model of the experimental device is built in SolidWorks2022 and then imported into ANSYS2023R2 Workbench to generate a mesh to ensure the accuracy of capturing the heat transfer dynamics of the system. (2) In the simulation setting, a transient simulation method is used to capture the time-temperature changes in the system thermal process in real time; In the solution stage, the pressure implicit segmentation operation method is selected as the solution strategy to ensure the calculation efficiency and accuracy; The finite volume method with staggered grid arrangement is used to achieve accurate spatial discretization; the momentum and energy equations are solved using the second-order upwind format to improve accuracy, while the pressure equation uses the PRESTO! format to ensure the stability and accuracy of the pressure-velocity coupling; (3) Based on the thermal simulation of the system, the following assumptions are made: (3.1) During the simulation, PCM and OMF-HDDA microcapsules were considered as a whole with consistent performance, and their internal composition and physical properties were completely consistent; (3.2)Assume that the fluid involved is incompressible; (3.3) It is assumed that the molten PCM fluid exhibits laminar flow characteristics, that is, its flow pattern is smooth and orderly without turbulent interference; (3.4)The terms related to viscous dissipation can be neglected; (3.5) Assume that the heat transfer process does not involve radiation effects and only focus on other heat transfer modes; (3.6) Throughout the entire operating range, the PCM is assumed to have uniform thermophysical properties; however, considering that the density ratio is less than 1, its density is estimated using the Boussines approximation; This approximation allows to consider the effect of buoyancy in natural convection, thus improving the simulation accuracy of PCM behavior; (4) Control equations: In simulating the heating and cooling process of the MOSFET system, the continuity equation, energy equation, and momentum equation are considered; Here are the equations that govern continuity and momentum: where Sx, Sy, and Sz represent the momentum source terms in the x, y, and z directions, respectively, and are applicable to the convective phase change process; the source terms are given by: Among them, u, v, w are velocities in each direction, t is time, ρ is density, P is pressure, μ is dynamic viscosity, g is gravitational acceleration, β is thermal expansion coefficient, T is temperature; Amushy is the mushy zone constant, λ represents the liquid volume fraction, ∈ prevents the denominator from being zero; The energy equation is as follows: The specific enthalpy (H) of PCM can be expressed as the sum of sensible enthalpy (h) and latent heat (ΔH): H=h+ΔH The calculation formula of sensible heat enthalpy is: Among them, C p is the specific heat, L is the latent heat, and λ is the liquid fraction. k represents the thermal conductivity of PCM, ΔH is the latent heat content, and h ref and T ref are the reference enthalpy and reference temperature respectively. The temperature dependence of the liquid fraction λ is as follows: This relationship reflects the significant phase change characteristics of PCM due to temperature changes during the charging and discharging process.

10. Application of microfluidic synthesized ferrofluid microcapsules in the field of electronic chip heat dissipation.

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