Preparation method, product and application of high-thermal-conductivity nanoscale phase change microcapsule

Abstract

The present application relates to the field of concrete and deepwater oil and gas field development cementing, in particular to a kind of preparation method, product and application of high thermal conductivity nanoscale phase change microcapsule.The preparation method includes the following steps: high thermal conductivity nanomaterial is treated by hydrophobic with silane coupling agent, and hydrophobic high thermal conductivity nanomaterial is obtained;Phase change material, epoxy resin and curing agent are mixed evenly, then hydrophobic high thermal conductivity nanomaterial is added and mixed evenly, and oil phase mixture is obtained;Cationic emulsifier and non-ionic emulsifier are dissolved in water to obtain aqueous solution;Under stirring condition, oil phase mixture is added into aqueous solution, the obtained emulsion is reacted at a certain temperature, then the obtained solid is centrifuged and freeze-dried, and high thermal conductivity nanoscale phase change microcapsule is obtained.The high thermal conductivity nanoscale phase change microcapsule has heat absorption function, can reduce the hydration heat of cement, and has no negative effect on the early compressive strength of cement stone, solves the deficiency of low hydration heat cement for current deepwater cementing.

Description

Technical Field

[0001] The present invention relates to the field of concrete and deepwater oil and gas field development cementing, and in particular to a preparation method, product and application of high-thermal-conductivity nano-scale phase-change microcapsules. Background Art

[0002] Deepwater areas are rich in oil and gas resources and offer significant exploration prospects. Low temperatures and the decomposition of natural gas hydrates (NGH) are two major challenges in deepwater oil and gas exploration. Delayed hydration of cement slurry in low-temperature environments leads to slow development of the mechanical properties of the cement stone, making it easy for fluids such as oil, gas, and water in the formation to invade the cement sheath, causing blowouts. Furthermore, the high heat released by cement slurry hydration causes the endothermic decomposition of NGHs, generating large amounts of gas under pressure that enters the cement slurry. This leads to sustained high pressure within the cement sheath, cracks, and compromised cementing quality.

[0003] Recent research has shown that adding phase change materials (PCMs) to cement can effectively reduce the heat of hydration. However, PCMs have low density and poor compatibility with cement components, making them unsuitable for direct use in cement. Instead, they are encapsulated in a shell to form phase change microcapsules. Currently, microcapsule shell materials primarily consist of organic polymers (formaldehyde resin, melamine resin, phenolic resin, etc.) and inorganic materials (calcium carbonate, silica, titanium dioxide, etc.). Inorganic materials have better compatibility with cement paste and exhibit excellent thermal conductivity. However, inorganic shell materials have poor encapsulation properties, resulting in large microcapsules and low phase change enthalpy. Compared to inorganic shell materials, organic polymers offer better encapsulation, chemical stability, and mechanical strength. However, organic polymer-shelled phase change microcapsules have low thermal conductivity, resulting in reduced heat absorption efficiency. Furthermore, research results indicate that the addition of phase change microcapsules, regardless of whether the shell material is organic or inorganic, inevitably negatively impacts the mechanical properties of the cement paste. Summary of the Invention

[0004] Based on the above, the present invention provides a method for preparing, producing, and applying high-thermal-conductivity nanoscale phase-change microcapsules. These nanoscale phase-change microcapsules exhibit high thermal conductivity and phase-change enthalpy, reducing the heat of cement hydration without negatively impacting cement paste strength. These microcapsules address current shortcomings of phase-change microcapsules for deepwater cementing.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a method for preparing high thermal conductivity nanoscale phase change microcapsules, comprising the following steps:

[0007] A silane coupling agent is used to perform hydrophobic treatment on the high thermal conductivity nanomaterial to obtain a hydrophobic high thermal conductivity nanomaterial;

[0008] Mixing a phase change material, an epoxy resin, and a curing agent to obtain an oil phase solution; adding a hydrophobized high thermal conductivity nanomaterial to the oil phase solution and mixing to obtain an oil phase mixture;

[0009] dissolving a cationic emulsifier and a nonionic emulsifier in water to obtain an aqueous solution;

[0010] adding the oil phase mixture to the aqueous solution under stirring conditions to obtain an emulsion;

[0011] The emulsion is reacted and then centrifuged to obtain a solid; the solid is freeze-dried to obtain the high thermal conductivity nanoscale phase change microcapsules.

[0012] The second technical solution of the present invention is a high thermal conductivity nanoscale phase change microcapsule prepared according to the preparation method.

[0013] The third technical solution of the present invention is the application of the high thermal conductivity nano-scale phase change microcapsules in cement.

[0014] The present invention discloses the following technical effects:

[0015] The present invention improves the dispersibility of nanomaterials in the oil phase by hydrophobically modifying the highly thermally conductive nanomaterials, making it easier for them to form a heat conduction path, thereby improving the thermal conductivity of the microcapsules. Secondly, using epoxy resin as a shell, the phase change material can be wrapped to avoid leakage of the phase change material during the phase change process. In addition, the hydroxyl groups on the surface of the epoxy resin can improve the dispersibility of the cement slurry particles, thereby promoting more uniform hydration of the cement slurry, producing a more dense cement stone structure, and promoting the strength development of the cement stone. Secondly, compared with micron-sized phase change microcapsules, nanoscale phase change microcapsules can be better dispersed in the cement slurry, avoiding the formation of large stress defects in the cement stone. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 SEM images and TEM images of the high thermal conductivity nanoscale phase change microcapsules prepared in Example 1, Example 2 and Example 3; wherein, (a) is the SEM image of Example 1, (b) is the SEM image of Example 2, (c) is the SEM image of Example 3, and (d) is the TEM image of Example 2.

[0018] Figure 2Phase change enthalpy diagrams of the high thermal conductivity nanoscale phase change microcapsules prepared in Example 1, Example 4 and Example 5.

[0019] Figure 3 Graph showing thermal conductivity of high thermal conductivity nanoscale phase change microcapsules prepared in Example 1, Example 2, and Example 3.

[0020] Figure 4 This is a hydration heat test diagram of oil well cement slurry added with different amounts of high thermal conductivity nano-scale phase change microcapsules prepared in Example 1.

[0021] Figure 5 The compressive strength of oil well cement stone mixed with different amounts of high thermal conductivity nano-scale phase change microcapsules prepared in Example 1 after 1 day, 2 days and 3 days. DETAILED DESCRIPTION

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0024] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0025] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] Phase change materials (PCMs) are substances that change state and provide latent heat while maintaining a constant temperature. They possess advantages such as high latent heat of fusion and high thermal storage density. They can generally be categorized as organic and inorganic PCMs. Organic PCMs are currently the most popular type of PCM due to their excellent chemical stability and high thermal conductivity. They absorb and release heat through their melting and solidification processes, thereby achieving energy storage and temperature control. Their relative ease of use has led to widespread commercial application. In the construction industry, for example, PCMs can be used in building envelopes, roofs, floors, domestic hot water tanks, and energy equipment. In the food industry, they can be used in refrigerators, food packaging, and transportation systems. However, organic PCMs undergo a phase change process, transforming from a solid to a liquid phase, exhibiting inherent drawbacks such as low thermal conductivity and leakage. This reduces the material's thermal storage efficiency and hinders its practical application. Therefore, for most applications, solid-liquid organic PCMs require encapsulation or form-stabilization methods to seal them.

[0028] Microencapsulation is a micro-packaging technology that encapsulates tiny solid, liquid, or gaseous materials within a shell of a natural or synthetic polymer matrix to protect unstable or sensitive functional materials. Therefore, microencapsulating phase change materials can effectively leverage their energy storage properties. The main advantages of microencapsulated phase change materials over PCMs are: ① a larger heat transfer area; ② reduced reactivity of the PCM to the external environment, facilitating control of changes in the volume of the phase change material. The present invention proposes the preparation of highly thermally conductive nanoscale phase change microcapsules with heat absorption capabilities, capable of reducing the heat of cement hydration while having no negative impact on the compressive strength of the cement paste. Phase change microcapsules are formed by encapsulating the phase change material with epoxy resin, and the addition of hydrophobic, highly thermally conductive nanomaterials enhances the heat absorption efficiency of the microcapsules. The phase change material absorbs the heat released by cement hydration, reducing the heat of cement hydration; and the hydroxyl groups on the surface of the epoxy resin are utilized to improve the dispersibility of the cement slurry particles, thereby increasing the compressive strength of the cement paste.

[0029] A first aspect of the present invention provides a method for preparing high thermal conductivity nanoscale phase change microcapsules, comprising the following steps:

[0030] A silane coupling agent is used to perform hydrophobic treatment on the high thermal conductivity nanomaterial to obtain a hydrophobic high thermal conductivity nanomaterial;

[0031] Mixing a phase change material, an epoxy resin, and a curing agent to obtain an oil phase solution; adding a hydrophobized high thermal conductivity nanomaterial to the oil phase solution and mixing to obtain an oil phase mixture;

[0032] dissolving a cationic emulsifier and a nonionic emulsifier in water to obtain an aqueous solution;

[0033] Adding the oil phase mixture to the aqueous solution and stirring at high speed for a certain period of time to obtain a stable emulsion;

[0034] The emulsion is reacted and then centrifuged to obtain a solid; the solid is freeze-dried to obtain the high thermal conductivity nanoscale phase change microcapsules.

[0035] In some embodiments of the present invention, the silane coupling agent is vinyltriethoxysilane, vinyltrimethoxysilane or octadecyltrimethoxysilane; the high thermal conductivity nanomaterial is boron nitride; the mass ratio of the silane coupling agent to the high thermal conductivity nanomaterial is (1-2):1; the hydrophobic treatment is specifically adding the high thermal conductivity nanomaterial to a silane coupling agent solution and reacting at 60-80°C for 4-6 hours; the solvent of the silane coupling agent solution is acetic acid aqueous solution; the pH of the silane coupling agent solution is 2-6; and the concentration of the silane coupling agent in the silane coupling agent solution is 0.02-0.04 g / mL.

[0036] The hydrophobic treatment also includes a step of ultrasonic dispersion before the hydrophobic treatment; after the hydrophobic treatment, the solid matter is centrifugally separated and then washed, dried and ground; the drying temperature is 90°C.

[0037] In some embodiments of the present invention, the phase change material is methyl stearate or ethyl stearate; the epoxy resin is epoxy resin E-51, epoxy resin CYDH-3000, or epoxy resin NP170; the curing agent is 4,4'-diaminodicyclohexylmethane (DDCM) or 3,3'-diethyl-4,4'-diaminodiphenylmethane (DEDDM); the mass ratio of the phase change material to the epoxy resin is (2-3):1; and the mass ratio of the epoxy resin to the curing agent is 1:0.3. The phase change material and epoxy resin have a significant impact on the phase change enthalpy of the phase change microcapsules. Excessive epoxy resin usage reduces the phase change enthalpy of the microcapsules, while insufficient epoxy resin usage prevents complete encapsulation of the phase change material, leading to leakage. Therefore, the present invention preferably limits the amounts of phase change material and epoxy resin to the above-mentioned ratio range.

[0038] In some embodiments of the present invention, the mass ratio of the oil phase solution to the hydrophobized high thermal conductivity nanomaterial is (8.5-10):(0.09-0.3).

[0039] When the hydrophobized high thermal conductive nanomaterial is added to the oil phase solution and mixed to prepare the oil phase mixture, a cell crusher with a power of 800W is used to ultrasonically mix the oil phase solution and the hydrophobized high thermal conductive nanomaterial for 10-20 minutes.

[0040] In some embodiments of the present invention, the cationic emulsifier is dodecyltrimethylammonium bromide or dodecyltrimethylammonium chloride; the nonionic emulsifier is dodecylphenol polyoxyethylene ether (OP-10), sorbitan fatty acid ester (Span-80) or polysorbate 20 (Tween-20); the concentration of the cationic emulsifier in the aqueous solution is 0.13-0.15 g / mL; the concentration of the nonionic emulsifier in the aqueous solution is 0.4-0.45 g / mL.

[0041] In some embodiments of the present invention, the mass volume ratio of the oil phase mixture to the aqueous solution is (9-11) g:100 mL; when preparing the stable emulsion, the stirring conditions are: stirring at a speed of 8000-12000 r / min for 8-10 min.

[0042] In the present invention, the particle size of the microcapsules is affected by the amount of emulsifier used and the stirring speed. The present invention limits the emulsifier concentration to: the concentration of the cationic emulsifier in the aqueous solution is 0.13-0.15 g / mL; the concentration of the nonionic emulsifier in the aqueous solution is 0.4-0.45 g / mL; the stirring speed and time are limited to: stirring at a speed of 8000-12000 r / min for 8-10 minutes; the phase change microcapsules prepared within the above parameter range are nanometer-sized; when the emulsifier concentration and stirring conditions exceed the above-mentioned parameter range, both will affect the particle size of the prepared microcapsules, and the preparation of nanometer-sized phase change microcapsules cannot be achieved.

[0043] In some embodiments of the present invention, the reaction temperature is 80-100° C. and the reaction time is 4-6 h.

[0044] The present invention does not impose any particular limitation on freeze-drying parameters such as pressure, temperature, and time, and the freeze-drying parameters commonly used in the art may be used.

[0045] After the emulsion reaction is completed, the centrifugal speed is 8000-12000 r / min and the time is 8-10 minutes.

[0046] The second aspect of the present invention provides a high thermal conductivity nanoscale phase change microcapsule prepared according to the preparation method.

[0047] The third aspect of the present invention provides the use of the high thermal conductivity nano-scale phase change microcapsules in cement.

[0048] In some embodiments of the present invention, the amount of the high thermal conductivity nano-scale phase change microcapsules added to cement is 1-5% of the mass of the cement.

[0049] The technical solutions described in the present application are conventional solutions in the art if not specifically stated, and the reagents or raw materials used are purchased from commercial channels or are already disclosed if not specifically stated.

[0050] The cement used in the embodiments of the present application is Jiahua G-grade oil well cement; other types of oil well cement can also be used in the present application.

[0051] The mass unit in each embodiment of the present application can be grams or kilograms or other mass units.

[0052] The technical solutions provided by the present application will be described in detail below in conjunction with the embodiments, but they should not be understood as limiting the scope of protection of the present application.

[0053] Example 1

[0054] The preparation method of high-thermal-conductivity nanoscale phase change microcapsules (referred to as phase change microcapsules) is as follows:

[0055] (1) Add acetic acid to 100 mL of water to adjust the pH to 4, then add 0.02 g / mL of vinyl triethoxysilane, and fully stir and dissolve. Add 1 g of boron nitride to the above silane coupling agent solution, ultrasonically disperse, and then add to a flask, and react at 60°C for 4 h. After the reaction is completed, centrifuge to separate out the solid material, wash with deionized water, and then dry and grind to obtain hydrophobic boron nitride (no requirement for the particle size of grinding, which can be ground into fine powder).

[0056] (2) Weigh 6 g of methyl stearate, melt it at 60°C, then add 3 g of epoxy resin E51, stir and mix thoroughly, then add 0.9 g of curing agent DDCM, and stir and mix again to form an oil phase solution. Add 0.099 g of hydrophobic boron nitride, and ultrasonically treat for 10 min at a power of 800 w to obtain an oil phase mixture.

[0057] (3) Add 0.14 g of dodecyltrimethylammonium bromide and 0.44 g of OP-10 to 100 mL of water, stir and fully dissolve to obtain a uniform aqueous solution, and heat the aqueous solution in a 60°C water bath.

[0058] (4) Under the stirring speed of 12000 r / min, add 10.197 g of the oil phase mixture to 100 mL of the aqueous solution, and then continuously stir for 10 min to obtain a uniform emulsion.

[0059] (5) Place the uniform emulsion in a 90°C water bath and react for 6 h, then centrifuge to obtain the solid part, and freeze-dry to obtain powder-like phase change microcapsules.

[0060] Example 2

[0061] The preparation method of high-thermal-conductivity nanoscale phase change microcapsules is as follows:

[0062] (1) Acetic acid was added to 100 mL of water to adjust the pH to 3, and then 0.03 g / mL of vinyltriethoxysilane was added and stirred thoroughly to dissolve. 2 g of boron nitride was added to the above silane coupling agent solution, ultrasonically dispersed, and then added to a flask. The mixture was reacted at 60° C. for 4 h. After the reaction, the solid matter was separated by centrifugation, washed with deionized water, dried, and ground to obtain hydrophobized boron nitride.

[0063] (2) 6 g of ethyl stearate was weighed and melted at 60°C. 3 g of epoxy resin CYDH-3000 was added and stirred thoroughly. 0.9 g of curing agent DDCM was added and stirred again to form an oil phase solution. 0.198 g of hydrophobized boron nitride was added and ultrasonicated at 800 W for 10 min to obtain an oil phase mixture.

[0064] (3) Add 0.14 g of dodecyltrimethylammonium bromide and 0.44 g of OP-10 to 100 mL of water, stir and dissolve thoroughly to obtain a uniform aqueous solution, and place the aqueous solution in a water bath at 60°C for constant temperature heating.

[0065] (4) At a stirring speed of 8000 r / min, 10.098 g of the oil phase mixture was added to 100 mL of the aqueous solution, and then stirred for 10 min to obtain a uniform emulsion.

[0066] (5) The uniform emulsion was placed in a 90°C water bath for reaction for 6 h. After the reaction was completed, the solid portion was obtained by centrifugation and freeze-dried to obtain powdered phase change microcapsules.

[0067] Example 3

[0068] The preparation method of high thermal conductivity nano-scale phase change microcapsules comprises the following steps:

[0069] (1) Acetic acid was added to 100 mL of water to adjust the pH to 4, and then 0.02 g / mL of vinyltriethoxysilane was added and stirred thoroughly to dissolve. 1 g of boron nitride was added to the above silane coupling agent solution, ultrasonically dispersed, and then added to a flask. The mixture was reacted at 60° C. for 4 h. After the reaction, the solid matter was separated by centrifugation, washed with deionized water, dried, and ground to obtain hydrophobized boron nitride.

[0070] (2) 6 g of ethyl stearate was weighed and melted at 60°C. 3 g of epoxy resin CYDH-3000 was added and stirred thoroughly. 0.9 g of curing agent DDCM was added and stirred again to form an oil phase solution. 0.297 g of hydrophobically modified boron nitride was added and ultrasonicated at 800 W for 10 min to obtain an oil phase mixture.

[0071] (3) Add 0.15 g of dodecyltrimethylammonium bromide and 0.43 g of OP-10 to 100 mL of water, stir and dissolve thoroughly to obtain a uniform aqueous solution, and place the aqueous solution in a water bath at 60°C for constant temperature heating.

[0072] (4) At a stirring speed of 8000 r / min, 9.197 g of the oil phase mixture was added to 100 mL of the aqueous solution, and then stirred for 10 min to obtain a uniform emulsion.

[0073] (5) The uniform emulsion was placed in a 100°C water bath for 6 h. After the reaction was completed, the solid portion was obtained by centrifugation and freeze-dried to obtain powdered phase change microcapsules.

[0074] Example 4

[0075] The preparation method of high thermal conductivity nano-scale phase change microcapsules comprises the following steps:

[0076] (1) Acetic acid was added to 100 mL of water to adjust the pH to 4, and then 0.02 g / mL of vinyltriethoxysilane was added and stirred thoroughly to dissolve. 2 g of boron nitride was added to the above silane coupling agent solution, ultrasonically dispersed, and then added to a flask. The mixture was reacted at 60° C. for 6 h. After the reaction, the solid matter was separated by centrifugation, washed with deionized water, dried, and ground to obtain hydrophobized boron nitride.

[0077] (2) 6 g of methyl stearate was weighed and melted at 60°C. 3 g of epoxy resin NP170 was added and stirred thoroughly. 0.9 g of curing agent DDCM was added and stirred again to form an oil phase solution. 0.297 g of hydrophobically modified boron nitride was added and ultrasonicated at 800 W for 10 min to obtain an oil phase mixture.

[0078] (3) Add 0.15 g of dodecyltrimethylammonium bromide and 0.43 g of OP-10 to 100 mL of water, stir and dissolve thoroughly to obtain a uniform aqueous solution, and place the aqueous solution in a water bath at 60°C for constant temperature heating.

[0079] (4) At a stirring speed of 12000 r / min, 10.197 g of the oil phase mixture was added to 100 mL of the aqueous solution, and then stirred for 10 min to obtain a uniform emulsion.

[0080] (5) The uniform emulsion was placed in an 80°C water bath for reaction for 4 h. After the reaction was completed, the solid portion was obtained by centrifugation and freeze-dried to obtain powdered phase change microcapsules.

[0081] Example 5

[0082] The preparation method of high thermal conductivity nano-scale phase change microcapsules comprises the following steps:

[0083] (1) Acetic acid was added to 100 mL of water to adjust the pH to 6, and then 0.02 g / mL of vinyltriethoxysilane was added and stirred thoroughly to dissolve. 2 g of boron nitride was added to the above silane coupling agent solution, ultrasonically dispersed, and then added to a flask. The mixture was reacted at 60° C. for 6 h. After the reaction, the solid matter was separated by centrifugation, washed with deionized water, dried, and ground to obtain hydrophobized boron nitride.

[0084] (2) 6 g of methyl stearate was weighed and melted at 60°C. 2 g of epoxy resin E51 was added and stirred thoroughly. 0.6 g of curing agent DDCM was added and stirred again to form an oil phase solution. 0.297 g of hydrophobically modified boron nitride was added and ultrasonicated at 800 W for 10 min to obtain an oil phase mixture.

[0085] (3) Add 0.15 g of dodecyltrimethylammonium bromide and 0.43 g of OP-10 to 100 mL of water, stir and dissolve thoroughly to obtain a uniform aqueous solution, and place the aqueous solution in a water bath at 60°C for constant temperature heating.

[0086] (4) At a stirring speed of 10,000 r / min, 9.897 g of the oil phase mixture was added to 100 mL of the aqueous solution, and then stirred for 10 min to obtain a uniform emulsion.

[0087] (5) The uniform emulsion was placed in a 90°C water bath for reaction for 4 h. After the reaction was completed, the solid portion was obtained by centrifugation and freeze-dried to obtain powdered phase change microcapsules.

[0088] In order to detect whether the encapsulation process of the phase change material is successful, the microscopic morphology of the high thermal conductivity nanoscale phase change microcapsules (hereinafter referred to as phase change microcapsules) prepared in Example 1, Example 2, and Example 3 was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The phase change material, epoxy resin, and curing agent form a uniform oil phase solution. When added to an aqueous solution, the lipophilic group in the emulsifier faces the oil phase, and the hydrophilic group faces the aqueous solution. Under the action of mechanical stirring, the oil phase is evenly dispersed in the aqueous solution to form a stable emulsion. At high temperatures, the amine groups in the curing agent and the epoxy groups produce a ring-opening reaction, eventually forming a cross-linked network structure. The cured epoxy resin is incompatible with the phase change material and gradually precipitates out from the oil phase solution. Under the action of stirring and centrifugation, it is wrapped around the phase change material to form an encapsulation. The modified boron nitride increases in hydrophobicity and is essentially insoluble in aqueous solution. It can stably exist in the oil phase solution and, as the epoxy resin solidifies, is interspersed between the epoxy resin and the phase change material. Example 1, Example 2 and Example 3 show the appearance of phase change microcapsules with different contents of hydrophobized boron nitride added. Figure 1(SEM) shows that the microcapsules have a consistent spherical structure, with varying degrees of particle protrusions on the surface, which should be the hydrophobized boron nitride interspersed in the oil phase. As the amount of hydrophobized boron nitride increases, the number of surface particles also increases significantly. In addition, it can be seen that the hydrophobized boron nitride is embedded in the shell material rather than simply adhering to the surface. This shows that the hydrophobized boron nitride has good compatibility with epoxy resin and can be well embedded in the epoxy matrix. Figure 1 (TEM) shows that the microcapsules have a clear core-shell structure, and the hydrophobized boron nitride can be well dispersed and embedded in the core and shell of the microcapsules. The above results prove the successful synthesis of phase change microcapsules. Figure 1 It can also be seen that the particle size distribution of the high thermal conductivity nanoscale phase change microcapsules prepared in Examples 1, 2 and 3 of the present invention is nanoscale.

[0089] The phase transition enthalpy changes of Example 1, Example 4 and Example 5 were measured by differential scanning calorimetry (DSC). Figure 2 As shown. The phase change temperatures of the microcapsules prepared in Example 1, Example 4 and Example 5 are 42.8°C, 43.6°C, and 3.2°C, respectively, and the phase change enthalpies are 179.9 J / g, 179.4 J / g and 174.4 J / g, respectively. The phase change enthalpies of Example 1 and Example 4 are not much different. On the contrary, the phase change enthalpy of Example 5 is significantly reduced. This is because the less epoxy resin cannot completely wrap the phase change material. During the subsequent cleaning process, the phase change material is lost, resulting in a decrease in the phase change enthalpy of the phase change microcapsules. The thermal conductivity of the microcapsules prepared in Example 1, Example 2 and Example 3 was tested by a thermal conductivity meter, as shown Figure 3 As shown in the figure, it can be seen that with the increase of the amount of hydrophobic boron nitride added, the thermal conductivity of the microcapsules increases significantly, indicating that the hydrophobic boron nitride plays a good thermal conductivity role in the microcapsules.

[0090] The phase change microcapsules prepared in Example 1 were added to the cement system at 1%, 3% and 5% by mass of Jiahua G-grade oil well cement. The preparation method of the cement slurry referred to the standard GB / T.19139-2012 "Test Methods for Oil Well Cement". Figure 4 The hydration heat curve of the cement slurry with phase change microcapsules prepared in Example 1. The maximum hydration heat temperature of the pure cement slurry (Ref.) without any admixtures is 51.5°C. The cement slurries with 1%, 3% and 5% phase change microcapsules added (corresponding to Figure 4 CET 1％ , CET 3％ , CET 5％The maximum hydration heat temperatures were 47°C, 45°C, and 43°C, respectively. Compared to pure cement slurry, these temperatures were reduced by 8.7%, 12.6%, and 16.5%, respectively. This is due to the phase change material absorbing the heat released by cement hydration during the melting process. This demonstrates that the phase change microcapsules prepared in Example 1 can successfully regulate the exothermic temperature of cement hydration.

[0091] The phase change microcapsules prepared in Example 1 were added to the cement slurry system at 1%, 3% and 5% of the mass of Jiahua G-grade oil well cement. The preparation method of the cement slurry, the preparation method of the compressive strength sample and the test method were based on the standard GB / T.19139-2012 "Test Methods for Oil Well Cement". Figure 5 The compressive strength data for the phase-change microcapsules prepared in Example 1 are shown. As can be seen from the figure, the addition of microcapsules at different dosages consistently improves the early compressive strength of cement, with the compressive strength of pure cement reaching 22.14 MPa after 3 days of curing. The compressive strengths of cement paste containing 1%, 3%, and 5% phase-change microcapsules were 22.59 MPa, 22.92 MPa, and 23.09 MPa, respectively, after three days of curing, demonstrating that phase-change microcapsules enhance the early compressive strength of cement paste. This increase in the compressive strength of cement paste is attributed to the hydroxyl groups in the epoxy resin improving the dispersibility of cement particles. Hydroxyl groups and other polar groups adsorb onto cement particles, leading to electrostatic repulsion and reducing particle agglomeration. This results in a more even distribution of cement particles and fewer interparticle gaps, thereby increasing the compressive strength of the cement paste. Furthermore, compared to large micron-sized particles, nanoparticles are more easily and evenly dispersed in cement paste, preventing the formation of large pores in the cement paste that reduce its compressive strength.

[0092] The high thermal conductivity nanoscale phase change microcapsules of the present invention have thermal regulation capabilities, can effectively reduce the heat of cement hydration, improve the early compressive strength of cement paste, and ensure cementing safety. The high thermal conductivity nanoscale phase change microcapsules have a phase change material as a core and an epoxy resin as a shell. The epoxy resin is wrapped around the phase change material through emulsification and in-situ deposition methods to form phase change microcapsules, thereby avoiding leakage of the phase change material during use. The phase change material can reduce the hydration heat temperature by absorbing the heat released by cement hydration. The hydroxyl groups on the surface of the epoxy resin promote the uniform dispersion of cement particles, improve the density of the cement paste, and further improve the compressive strength of the cement paste. The high thermal conductivity nanoscale phase change microcapsules have the characteristics of simple preparation process, wide source of raw materials, easy practical engineering application, regulation of cement slurry hydration heat, and improvement of the compressive strength of cement paste.

[0093] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing high thermal conductivity nanoscale phase change microcapsules, characterized in that: The following steps are involved: A silane coupling agent is used to perform hydrophobic treatment on the high thermal conductivity nanomaterial to obtain a hydrophobic high thermal conductivity nanomaterial; Mixing phase change material, epoxy resin and curing agent to obtain an oil phase solution; adding a hydrophobized high thermal conductivity nanomaterial to the oil phase solution and mixing uniformly to obtain an oil phase mixture; dissolving a cationic emulsifier and a nonionic emulsifier in water to obtain an aqueous solution; adding the oil phase mixture to the aqueous solution under stirring conditions to obtain an emulsion; The emulsion is reacted and then centrifuged to obtain a solid; the solid is freeze-dried to obtain the high thermal conductivity nanoscale phase change microcapsules; The high thermal conductivity nanomaterial is boron nitride; The phase change material is methyl stearate or ethyl stearate; The curing agent is 4,4'-diaminodicyclohexylmethane or 3,3'-diethyl-4,4'-diaminodiphenylmethane; The cationic emulsifier is dodecyltrimethylammonium bromide or dodecyltrimethylammonium chloride; The nonionic emulsifier is dodecylphenol polyoxyethylene ether, sorbitan fatty acid ester or polysorbate-20.

2. The method for preparing high thermal conductivity nanoscale phase change microcapsules according to claim 1, characterized in that: The silane coupling agent is vinyltriethoxysilane, vinyltrimethoxysilane or octadecyltrimethoxysilane; the mass ratio of the silane coupling agent to the high thermal conductivity nanomaterial is (1-2):1; the hydrophobic treatment is specifically adding the high thermal conductivity nanomaterial to a silane coupling agent solution and reacting at 60-80° C. for 4-6 hours; the solvent of the silane coupling agent solution is acetic acid aqueous solution; and the pH of the silane coupling agent solution is 2-6.

3. The method for preparing high thermal conductivity nanoscale phase change microcapsules according to claim 1, characterized in that: The epoxy resin is epoxy resin E-51, epoxy resin CYDH-3000 or epoxy resin NP170; the mass ratio of the phase change material to the epoxy resin is (2-3):1; the mass ratio of the epoxy resin to the curing agent is 1:0.

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4. The method for preparing high thermal conductivity nanoscale phase change microcapsules according to claim 1, characterized in that: The mass ratio of the oil phase solution to the hydrophobized high thermal conductivity nanomaterial is (8.5-10):(0.09-0.3).

5. The method for preparing high thermal conductivity nanoscale phase change microcapsules according to claim 1, characterized in that: The concentration of the cationic emulsifier in the aqueous solution is 0.13-0.15 g / mL; the concentration of the nonionic emulsifier in the aqueous solution is 0.4-0.45 g / mL.

6. The method for preparing high thermal conductivity nanoscale phase change microcapsules according to claim 1, characterized in that: The mass volume ratio of the oil phase mixture to the aqueous solution is (9-11) g:100 mL; the stirring condition is: stirring at a speed of 8000-12000 r / min for 8-10 minutes.

7. The method for preparing high thermal conductivity nanoscale phase change microcapsules according to claim 1, characterized in that: The reaction temperature is 80-100° C. and the reaction time is 4-6 hours.

8. High thermal conductivity nanoscale phase change microcapsules prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the high thermal conductivity nano-scale phase change microcapsules according to claim 8 in cement.

10. The use according to claim 9, characterized in that The amount of the high thermal conductivity nano-scale phase change microcapsules added to cement is 1-5% of the mass of the cement.

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