High-suspension-property double-shell phase change nanocapsule as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of phase-change materials, and particularly discloses a high-suspension double-shell phase-change nanocapsule and a preparation method and application thereof, and the preparation method comprises the following steps: S1, preparing a water phase; s2, preparing an oil phase; s3, emulsifying: adding the oil phase into the water phase, and performing ultrasonic treatment; s4, polymerization: magnetically stirring, raising the temperature, and adjusting the pH value; s5, depositing silver bromide particles: mixing with deionized water, adding cetyltrimethylammonium bromide and potassium bromide, uniformly stirring, then adding silver nitrate, and stirring; and S6, forming a silver shell: adding hydroquinone, performing primary stirring, continuing to add the citric acid buffer solution and silver nitrate, and performing secondary stirring to grow the silver shell. According to the high-suspension-property double-shell phase change nanocapsule and the preparation method and application thereof, the density of the inner shell is low, the density of the outer silver shell is thin, the density of the nanocapsule can be reduced, the suspension stability of the capsule in fluid can be enhanced, the thermal response speed of the capsule can be increased, and the thermal response time can be shortened.

Description

Technical Field

[0001] This invention relates to the field of phase change materials technology, and in particular to a highly suspended double-shell phase change nanocapsule, its preparation method, and its application. Background Technology

[0002] Phase change materials (PCMs) are substances that absorb or release a large amount of latent heat during phase transitions, serving as the working medium for latent heat storage technologies. Thermal responsiveness is a key parameter characterizing the heat transfer capability of PCM nanocapsules. Furthermore, when double-shell PCM nanocapsules are applied in fluids, their suspension stability is a crucial performance parameter. Dispersing PCM nanocapsules in a fluid yields latent heat functional fluids (LFTFs). Due to the influence of PCM particles on fluid flow and heat transfer, LFTFs effectively improve the apparent specific heat and heat transfer properties of the fluid, thereby significantly enhancing its heat transfer capacity. For LFTFs, since the PCM nanocapsules, which play a major role, are distributed in a dispersed form within the fluid, the heat transfer of individual nanocapsules within the fluid is the fundamental factor limiting fluid performance.

[0003] In existing technologies, the prepared double-shell phase change nanocapsules suffer from high density and poor suspension, mainly due to the large thickness and density of the double shells. The large capsule size and shell thickness also result in relatively poor thermal responsiveness. Summary of the Invention

[0004] The purpose of this invention is to provide a highly suspended double-shell phase change nanocapsule, its preparation method, and its application. The inner shell has a low density and the outer silver shell is thin, which can reduce the density of the nanocapsule, enhance the suspension stability of the capsule in the fluid, and improve the thermal response speed and shorten the thermal response time of the capsule.

[0005] To achieve the above objectives, this invention provides a method for preparing highly suspended double-shell phase change nanocapsules, comprising the following steps: S1. Add citrate buffer to the sodium salt aqueous solution of styrene-maleic anhydride copolymer to adjust the pH of the system to 7, and stir evenly under neutral conditions in a water bath at 90-100℃ to obtain the aqueous phase; S2. Stearate butyl ester, isophorone diisocyanate, polyaspartic acid ester and polypropylene glycol are mixed in proportion, and then stirred evenly in a water bath at 25-30℃ to obtain the oil phase. S3, Emulsification: The oil phase obtained in S2 is added to the aqueous phase obtained in S1 to form a mixed system, and the mixed liquid is placed in an ultrasonic instrument for ultrasonication to obtain a stable emulsion; S4. Polymerization: The stable emulsion obtained in S3 is transferred to a magnetic stirrer and the temperature is raised to 90-100℃. The mixture is stirred and then the pH is adjusted to 7-8 with sodium hydroxide solution to terminate the reaction, thus obtaining BS / PU-PUA phase change nanocapsules. S5. Deposition of silver bromide particles: Dissolve the BS / PU-PUA phase change nanocapsules obtained in S4 in deionized water according to the ratio, add hexadecyltrimethylammonium bromide solution and potassium bromide solution, stir evenly, then add silver nitrate solution and stir to obtain a mixture; S6. Formation of the silver shell: Hydroquinone solution was added to the mixture obtained in S5, and the mixture was stirred once. Citrate buffer and silver nitrate solution were added again, and the silver shell was grown by stirring in the dark. After washing and drying, BS / PU-PUA / Ag phase change nanocapsules were obtained.

[0006] Preferably, in S1, the concentration of the sodium salt aqueous solution of styrene-maleic anhydride copolymer is 2wt%, and the preparation method of the sodium salt aqueous solution of styrene-maleic anhydride copolymer is to add 2g of sodium salt of styrene-maleic anhydride copolymer to 100ml of deionized water.

[0007] Preferably, in S2, the mass ratio of the butyl stearate, the isophorone diisocyanate, the polyaspartic acid ester, and the polypropylene glycol is 10:3.3:5:1.7.

[0008] Preferably, in S3, the ultrasonic power is 100-300w and the ultrasonic time is 5-10min.

[0009] Preferably, in step S4, the stirring speed is 300-500 rpm and the stirring time is 5-6 hours.

[0010] Preferably, in step S5, a 2 mmol / L hexadecyltrimethylammonium bromide solution, an 18 mmol / L potassium bromide solution, and an 80 mmol / L silver nitrate solution are used, wherein the ratio of the BS / PU-PUA phase change nanocapsule to the deionized water to the hexadecyltrimethylammonium bromide solution to the potassium bromide solution to the silver nitrate solution is 50 mL to 0.5 g to 0.1071 g to 0.1359 g.

[0011] Preferably, in step S6, a hydroquinone solution with a hydroquinone:water ratio of 1.5g:30mL is used, a citrate buffer solution with a pH of 3.4 is used, and a silver nitrate solution with a silver nitrate:water ratio of 1g:30mL is used, wherein the hydroquinone solution:the citrate buffer solution:the silver nitrate solution = 30mL:15ml:30ml.

[0012] Preferably, in S6, the first stirring time is 3-5 hours, and the second stirring time is 12-15 hours.

[0013] The present invention also provides a highly suspensible double-shell phase change nanocapsule, and the tanθ value of the double-shell phase change nanocapsule is 0.072. The calculation formula is as follows: ; where θ is the angle of deviation of the solid particle from the horizontal direction when moving downward; is the density of the phase change nanocapsule; is the fluid density, kg / m

[0016] ; is the acceleration of gravity, m / s 2 ; r is the radius of the particle in the fluid, m is the Boltzmann constant, J / k; is the thermodynamic temperature, K.

[0014] The present invention also provides an application of the highly suspensible double-shell phase change nanocapsule in a latent heat type functional fluid.

[0015] Therefore, by adopting the above-mentioned highly suspensible double-shell phase change nanocapsule, its preparation method and application, the beneficial effects of the present invention are as follows: The present invention improves the suspension of the nanocapsule from two aspects of reducing the particle size and density of the capsule: on the one hand, by optimizing the experimental operation conditions (such as ultrasonic power and ultrasonic time), the particle size of the butyl stearate / polyurea-polyurethane / silver double-shell phase change nanocapsule is reduced, and by adjusting the addition amount of silver nitrate, the thickness of the silver shell on the outer layer of the phase change nanocapsule is adjusted to reduce the particle size of the capsule; on the other hand, an organic material with a smaller density is selected as the inner shell of the capsule, that is, polyurea-polyurethane with a density of 1.1 g / cm 3 is used as the inner shell material of the phase change capsule, effectively reducing the overall density of the nanocapsule, and the thickness of the silver shell on the outer layer of the capsule is regulated by reducing the addition amount of silver nitrate to reduce the density of the capsule.

[0016] The double-shell phase change nanocapsule prepared by the present invention has suspension stability in the fluid: the smaller the movement direction angle θ and the smaller the tanθ value (0 < tanθ < 1), the better the suspension. The θ value of the BS / PU-PUA / Ag phase change nanocapsule is at least 4.118°, and the corresponding tanθ value is 0.072.

[0017] The double-shell phase change nanocapsule prepared by the present invention has thermal responsiveness in the fluid: reducing the thickness of the outer silver shell effectively improves the thermal response speed of the capsule and shortens the thermal response time. The complete thermal response time of the BS / PU-PUA / Ag phase change nanocapsule is 1.25×10 -6 s, and the thermal response time is extremely short.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 These are microscopic images of a highly suspended double-shell phase change nanocapsule of the present invention, its preparation method, and an application example 1, wherein (a) is a SEM image of the BS / PU-PUA phase change nanocapsule, (b) is a TEM image of the BS / PU-PUA phase change nanocapsule, and (c) is a SEM image of the BS / PU-PUA / Ag phase change nanocapsule. Figure 2 This is a schematic diagram of the movement direction of solid particles in a fluid, illustrating the highly suspended double-shell phase change nanocapsule of the present invention, its preparation method, and application example two. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0022] Example 1 A highly suspended double-shell phase change nanocapsule was prepared by first using butyl stearate as the core material and polyurea-polyurethane as the shell material. An in-situ polymerization method was employed, followed by ultrasonic dispersion to break the core material into uniform droplets, resulting in a phase change capsule with a uniform morphology and an organic shell coating. Subsequently, a liquid-phase reduction method was used to plate silver onto the surface of the organic shell capsule, yielding a polyurea-polyurethane / silver double-shell phase change capsule with excellent morphology and a uniform silver shell.

[0023] Its preparation method is as follows: S1. Preparation of aqueous phase: Add 2g of sodium salt of styrene-maleic anhydride copolymer to 100ml of deionized water, stir evenly under constant temperature water bath at 90℃, and adjust the pH of the solution to 7 with citric acid to help emulsify, thus obtaining the aqueous phase.

[0024] S2. Preparation of oil phase: Mix 10g of core material butyl stearate, 3.3g of isophorone diisocyanate, 5g of polyaspartic acid ester and 1.7g of polypropylene glycol, and then stir evenly under a constant temperature water bath at 25℃ to obtain the oil phase.

[0025] S3. Emulsification: The oil phase obtained in S2 is added to the aqueous phase obtained in S1 to form a mixed system. Then, the mixture is sonicated at room temperature with an ultrasonic power of 200W for 5 minutes to obtain a stable emulsion.

[0026] S4. Polymerization: The stable emulsion obtained in S3 was transferred to a magnetic stirrer and the temperature was slowly increased to 90°C. The mixture was stirred at 400 rpm for 5.5 h. The reaction was then terminated by adjusting the pH to 7 with a 20 wt% sodium hydroxide solution to obtain BS / PU-PUA phase change nanocapsules.

[0027] S5. Deposition of silver bromide particles: Dissolve 1g of BS / PU-PUA phase change nanocapsules in 50mL of deionized water, add cetyltrimethylammonium bromide solution (0.5g, 2mmol / L) and potassium bromide solution (0.1071g, 18mmol / L), stir evenly on a magnetic stirrer (400rpm), then add 10mL of prepared silver nitrate solution (80mmol / L), stir for 1h to obtain a mixture.

[0028] S6. Formation of the silver shell: Add 30 mL of hydroquinone solution (1.5 g) to the mixture obtained in S5, stir thoroughly for 3 h, then add 15 mL of citrate buffer solution (pH=3.4) and 30 mL of silver nitrate solution (1 g), stir in the dark for 12 h to grow the silver shell, wash and dry to obtain BS / PU-PUA / Ag phase change nanocapsules.

[0029] Example 2 Using the BS / PU-PUA / Ag phase change nanocapsules obtained in Example 1, the phase change nanocapsules were dispersed in a fluid to prepare a latent heat functional fluid. The suspension properties of the phase change nanocapsules in this suspension system were calculated as follows: In a suspension system, dispersed solid particles are all subject to gravitational settling. When their density is higher than that of the base liquid, the terminal velocity of the particles in the Stokes region of the gravitational field will induce settling. Assuming the particles are uniform spheres, the terminal velocity of the solid particles in the Stokes region is given by the following equation:

[0030] ; in, The terminal velocity is in m / s; Capsule density, kg / m³ 3 ; Fluid density, kg / m³ 3 ; The acceleration due to gravity is m / s². 2 ; Let be the diameter of the spherical solid particle, in meters (m). Let be the dynamic viscosity of the fluid, Pa·s.

[0031] Besides sedimentation, Brownian motion of particles in a fluid also plays a crucial role in particle suspension in the base liquid. The random motion of suspended solid particles caused by frequent collisions with surrounding liquid molecules is called Brownian motion. The smaller the solid particle size, the stronger its tendency to move in the base liquid, and the easier it is to generate irregular motion deviating from the vertical direction. For solid particles in a suspension system, the free diffusion coefficient and diffusion time are determined by the following formulas:

[0032] ; ; in, m is the free diffusion coefficient. 2 / s; Boltzmann constant, J / k; K represents the thermodynamic temperature. ρ is the dynamic viscosity of the fluid, Pa·s; r is the radius of the particles in the fluid, m; Let be the diffusion time of the particle, in seconds, when the diffusion distance is approximately equal to r.

[0033] Derive the Brownian diffusion velocity of the particles : ; In summary, the suspension property of solid particles in a suspension system is influenced by both gravitational sedimentation and Brownian diffusion: when gravitational sedimentation dominates, particles move downwards and tend to settle; conversely, Brownian motion generally favors diffusion. This is because the direction of Brownian motion is uncertain, but except for the downward direction which leads to sedimentation, other directions promote diffusion, enabling particles to maintain a good suspension state in the system. For ease of calculation, the horizontal direction is taken as the average direction of Brownian diffusion of solid particles.

[0034] Based on the terminal velocity in the vertical direction and the Brownian diffusion velocity in the horizontal direction, a schematic diagram of the motion direction of a single solid particle in a fluid can be obtained, as shown below. Figure 2 As shown. The velocity in the vertical direction is the terminal velocity, and the velocity in the horizontal direction is the Brownian diffusion velocity. The motion angle θ is the angle by which the solid particle deviates from the horizontal direction when moving downwards. By analyzing the settling velocity model of particles in the suspension system using θ, the particle motion parameter is defined as follows:

[0035] ; according to This study investigates the velocity and suspension of solid particles during horizontal and vertical motion in a fluid: when hour, Brownian diffusion velocity is greater than terminal velocity, and particles primarily diffuse horizontally via Brownian diffusion, enabling them to remain suspended in the fluid. When hour, Particles with predominantly vertical terminal velocities are more prone to deposition; this range is defined as deposition. When Based on density and particle size, the suspension equilibrium curve of the solid particles can be obtained. The region below the suspension equilibrium curve is defined as the diffusion region; within this region... The smaller the value, the better the particle suspension; similarly, the area above the suspension equilibrium curve is defined as the sedimentation zone, within which... The higher the value, the worse the particle suspension.

[0036] The calculation formula is as follows:

[0037] Depend on The calculation formula yields, The value is positively correlated with both particle size and density; that is, in the same system, the suspension of particles in a fluid depends on their particle size and density: the smaller the particle size of a solid particle, the lower its density. The smaller the value, the better the suspension in the fluid.

[0038] The relevant parameters of the BS / PU-PUA / Ag phase change nanocapsules prepared in Example 1 ( =1.60g / cm 3 r=322nm, K B =1.38×10 -23 Substituting J / K, T=293.15K into the above... In the calculation formula, the corresponding tanθ is 0.072, and the minimum θ value is 4.118°, indicating good suspension.

[0039] Test 1. Morphological analysis The BS / PU-PUA phase change nanocapsules and BS / PU-PUA / Ag phase change nanocapsules prepared in Example 1 were analyzed. Figure 1 As shown in (a), the BS / PU-PUA phase change nanocapsules have a uniform morphology, consisting of smooth and dense spheres. Figure 1 As shown in (b), the core-shell structure of the BS / PU-PUA nanocapsule is clearly displayed. Figure 1As shown in (c), the BS / PU-PUA / Ag phase change nanocapsules obtained after silver plating all exhibit a regular spherical morphology, with a small amount of silver particles deposited on the surface of some capsules. This indicates the successful preparation of BS / PU-PUA / Ag phase change nanocapsules with good morphology and a nanocapsule particle size of 322 nm.

[0040] 2. Thermal Response Analysis Thermal responsiveness (LFTF) analysis was performed on the latent heat functional fluid prepared in Example 2. Due to the influence of phase change particles on fluid flow and heat transfer, LFTF effectively improved the apparent specific heat and heat transfer performance of the fluid, thereby greatly improving the fluid's heat transfer capacity. For LFTF, since the phase change nanocapsules that play a major role are distributed in the fluid in a dispersed form, the heat transfer of single nanocapsules in the fluid is the fundamental factor limiting the fluid performance.

[0041] A single-particle transient heat transfer model was established, and the thermal responsiveness of the phase change nanocapsule was characterized by the time it takes for the phase change nanocapsule to fully heat up to the fluid temperature. The shorter the thermal response time, the faster the thermal response speed, and the better the thermal responsiveness of the capsule.

[0042] First, the dimensions of the phase change nanocapsules were determined. Based on the measured encapsulation rate, the diameter of the core material (butyl stearate) particles was calculated to be 579 nm, the thickness of the polyurea-polyurethane shell to be 17.54 nm, and the thickness of the silver shell to be 14.98 nm. Next, the thermophysical parameters of the nanocapsules and the fluid were determined (e.g., at a temperature of 40°C, the density of the latent heat functional fluid containing 5%, 10%, and 15% BS / PU-PUA / Ag phase change nanocapsules was 1065.55-1157.20 kg / m³). 3 The specific heat capacity is between 4.88 and 5.58 J / g·K, and the thermal conductivity ranges from 0.6875 to 0.9286 W / (m²). Finally, assuming the fluid temperature is 80℃, its heating process is simulated to obtain the temperature response time. The complete thermal response time of the BS / PU-PUA / Ag phase change nanocapsules is 1.25 × 10⁻⁶. -6 The thermal response time is extremely short.

[0043] Therefore, the present invention employs the above-mentioned highly suspended double-shell phase change nanocapsule, its preparation method and application, with a low density inner shell and a thin outer silver shell, which can reduce the density of the nanocapsule, enhance the suspension stability of the capsule in the fluid, and also improve the thermal response speed and shorten the thermal response time of the capsule.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing highly suspended double-shell phase change nanocapsules, characterized in that, Includes the following steps: S1. Add citrate buffer to the sodium salt aqueous solution of styrene-maleic anhydride copolymer, and stir evenly under neutral conditions in a water bath at 90-100℃ to obtain the aqueous phase. S2. Stearate butyl ester, isophorone diisocyanate, polyaspartic acid ester and polypropylene glycol are mixed in proportion, and then stirred evenly in a water bath at 25-30℃ to obtain the oil phase. S3, Emulsification: The oil phase obtained in S2 is added to the aqueous phase obtained in S1 to form a mixed system, and the mixed liquid is placed in an ultrasonic instrument for ultrasonication to obtain a stable emulsion; S4. Polymerization: The stable emulsion obtained in S3 is transferred to a magnetic stirrer and the temperature is raised to 90-100℃. The mixture is stirred and then the pH is adjusted to 7-8 with sodium hydroxide solution to terminate the reaction, thus obtaining BS / PU-PUA phase change nanocapsules. S5. Deposition of silver bromide particles: Dissolve the BS / PU-PUA phase change nanocapsules obtained in S4 in deionized water according to the ratio, add hexadecyltrimethylammonium bromide solution and potassium bromide solution, stir evenly, then add silver nitrate solution and stir to obtain a mixture; S6. Formation of the silver shell: Hydroquinone solution was added to the mixture obtained in S5, and the mixture was stirred once. Citrate buffer and silver nitrate solution were added again, and the silver shell was grown by stirring in the dark. After washing and drying, BS / PU-PUA / Ag phase change nanocapsules were obtained.

2. The method for preparing a highly suspended double-shell phase change nanocapsule according to claim 1, characterized in that, In S1, the concentration of the sodium salt aqueous solution of the styrene-maleic anhydride copolymer is 2 wt%.

3. The method for preparing a highly suspended double-shell phase change nanocapsule according to claim 1, characterized in that, In S2, the mass ratio of butyl stearate, isophorone diisocyanate, polyaspartic acid ester and polypropylene glycol is 10:3.3:5:1.

7.

4. The method for preparing a highly suspended double-shell phase change nanocapsule according to claim 1, characterized in that, In S3, the ultrasonic power is 100-300w and the ultrasonic time is 5-10min.

5. The method for preparing a highly suspended double-shell phase change nanocapsule according to claim 1, characterized in that, In S4, the stirring speed is 300-500 rpm and the stirring time is 5-6 hours.

6. The method for preparing a highly suspended double-shell phase change nanocapsule according to claim 1, characterized in that, In S5, a 2 mmol / L hexadecyltrimethylammonium bromide solution, an 18 mmol / L potassium bromide solution, and an 80 mmol / L silver nitrate solution are used. The ratio of the BS / PU-PUA phase change nanocapsule: the deionized water: the hexadecyltrimethylammonium bromide: the potassium bromide: the silver nitrate solution is 50 mL: 0.5 g: 0.1071 g: 0.1359 g.

7. The method for preparing a highly suspended double-shell phase change nanocapsule according to claim 1, characterized in that, In S6, a hydroquinone solution with a hydroquinone:water ratio of 1.5g:30mL is used, a citrate buffer solution with a pH of 3.4 is used, and a silver nitrate solution with a silver nitrate:water ratio of 1g:30mL is used. The ratio of hydroquinone solution:citrate buffer solution:silver nitrate solution is 30mL:15ml:30ml.

8. The method for preparing a highly suspended double-shell phase change nanocapsule according to claim 1, characterized in that, In S6, the first stirring time is 3-5 hours, and the second stirring time is 12-15 hours.

9. A double-shell phase change nanocapsule prepared by the method for preparing highly suspended double-shell phase change nanocapsules according to any one of claims 1-8, characterized in that, The tanθ value of the double-shell phase change nanocapsule is 0.

072. The calculation formula is as follows: ； Where θ is the angle at which the solid particle deviates from the horizontal direction when it moves downward; Density of phase change nanocapsules Fluid density, kg / m³ 3 ; The acceleration due to gravity is m / s². 2 ; r is the radius of the particle in the fluid, m Boltzmann constant, J / k; K represents the thermodynamic temperature.

10. The application of the highly suspended double-shell phase change nanocapsule as described in claim 9 in latent heat functional fluids.

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