Carbon nanotube foam composite phase change microcapsule and preparation method thereof

Abstract

The invention belongs to the technical field of phase change materials, and particularly relates to a carbon nanotube foam composite phase change microcapsule and a preparation method thereof. The carbon nanotube foam composite phase change microcapsule comprises carbon nanotube foam and a solid phase change material packaged in the carbon nanotube foam, and the solid phase change material is selected from one of n-octadecane, fatty acid, neopentyl glycol and polyethylene glycol. According to the method, the high porosity and the porous structure of the carbon nanotube foam are utilized, so that the loading capacity of the phase change material is enhanced, and the heat conductivity and the shape stability of the composite material are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of phase change materials, and more particularly relates to a carbon nanotube foam composite phase change microcapsule and a preparation method thereof. BACKGROUND

[0002] The phase change capsule is a new type of functional material, which encapsulates the phase change material in the microcapsule, so that it has better stability and applicability while maintaining the phase change characteristics. The micro characteristics of this phase change capsule combine with macro application, showing great potential in energy storage, heat pipe and other fields. However, the current phase change capsule wall material (such as high polymer material) has low thermal conductivity, which hinders the rapid heat transfer to the core material, resulting in the decrease of overall heat storage and heat release efficiency. Secondly, after experiencing multiple phase change cycles, the shell wall of the phase change capsule will gradually fail due to thermal expansion and contraction or chemical corrosion, the core material leakage rate increases, and the energy storage density decreases.

[0003] Chinese patent CN 111518518 A discloses a multi-walled graphene oxide phase change microcapsule material and a preparation method, the specific steps of which include: after the reduction of graphene oxide (rGO), the surfactant and long-chain n-alkane are emulsified and dispersed, the precursor such as tetraethyl orthosilicate is added, and the phase change microcapsule is formed after 16 hours of reaction under the catalysis of ammonia. The thermal conductivity of the material is 0.1784-0.1997 W / m·K, although the thermal conductivity of the pure alkane phase change microcapsule is improved by 57.33-62.83% after the addition of graphene oxide, but the degree of performance improvement may still have certain limitations.

[0004] Therefore, there is an urgent need for a composite phase change microcapsule material with excellent performance. SUMMARY

[0005] (I) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a carbon nanotube foam composite phase change microcapsule and a preparation method thereof, which solves the technical problems of microcapsule shell wall failure, core material leakage rate increase and energy storage density decrease after multiple phase change cycles.

[0007] (II) Technical solutions

[0008] In the first aspect, the present application provides a carbon nanotube foam composite phase change microcapsule, which comprises a carbon nanotube foam and a solid phase change material encapsulated in the carbon nanotube foam, wherein the solid phase change material is selected from one of n-octadecane, fatty acid, neopentyl glycol and polyethylene glycol.

[0009] In the second aspect, the present application provides a preparation method of the carbon nanotube foam composite phase change microcapsule of the first aspect, comprising the following steps:

[0010] S1, uniformly mixing the excess solid phase change material with the chemically modified carbon nanotube foam by dry mixing;

[0011] S2, heating the mixture obtained in step S1 in a vacuum oven to ensure complete melting of the solid phase change material, which makes the phase change material more easily combined with the carbon nanotube foam, and the liquid phase change material can completely fill the pore structure of the carbon nanotube foam under the driving of capillary action and pressure difference;

[0012] S3, heating in the oven to remove the remaining phase change material on the surface of the carbon nanotube foam, repeating multiple times until no phase change material is observed in the filter paper; finally obtaining the carbon nanotube foam composite phase change microcapsule.

[0013] Optionally, surface functionalization treatment of the carbon nanotube foam: placing the carbon nanotube foam in concentrated nitric acid with a mass fraction of 65-70%, ultrasonic refluxing at 60-120℃ for several hours, washing the product with deionized water until the pH value of the filtrate reaches 7; vacuum drying at 80℃ to ensure that the air in the pores of the carbon nanotube foam is completely discharged; this step chemically modifies the surface of the carbon nanotube foam by nitric acid oxidation.

[0014] Optionally, the average pore size of the carbon nanotube foam is 50-100nm, the inner diameter of the carbon nanotube foam is 10-20nm, and the outer diameter is 30-50nm.

[0015] The carbon nanotube foam is synthesized by chemical vapor deposition (CVD); ferrocene powder is dissolved in dichlorobenzene and introduced into a quartz tube at a feed rate of 0.13mL / min, using Ar and H2 as carrier gas, and the reaction temperature is set to 860℃.

[0016] Optionally, the ultrasonic-assisted refluxing time of the carbon nanotube foam is 4-24h.

[0017] Optionally, the vacuum drying time at 80℃ is 12-24h.

[0018] Optionally, the solid phase change material is selected from one of n-octadecane, fatty acid, neopentyl glycol and polyethylene glycol.

[0019] Optionally, the mass ratio of the solid phase change material to the chemically modified carbon nanotube foam is 10-30:1.

[0020] Optionally, in step S1, the dry mixing method is mechanical grinding.

[0021] Optionally, in step S2, the heating temperature is 60-100℃.

[0022] Optionally, in step S2, the mixture is heated in a vacuum oven for 4-10 hours.

[0023] Optionally, in step S3, the heating temperature for removing the remaining phase change material on the surface of the carbon nanotube foam is consistent with the temperature in step S2.

[0024] Optionally, the application of the carbon nanotube foam composite phase change microcapsule in building materials and industrial energy storage materials.

[0025] (III) Beneficial effects

[0026] The carbon nanotube foam composite phase change material of the present application adopts a three-dimensional network structure of carbon nanotube foam as an encapsulation shell of the phase change material, forming a composite structure system with carbon nanotube foam as the shell and phase change material as the core; at the structural level, it has the characteristics of ultra-light weight and ultra-high specific surface area, and can form a three-dimensional network architecture with uniform pore size distribution and through pores through precise control.

[0027] The present application effectively solves the material leakage problem caused by volume expansion during the solid-liquid phase change process of traditional phase change materials through the unique high strength and high elasticity mechanical properties of carbon nanotube foam, significantly improves the cycle stability of the encapsulation system; in addition, its three-dimensional porous structure not only enhances the mechanical strength of the microcapsule, but also provides a stable support frame, ensuring the structural integrity in repeated phase change cycles.

[0028] The three-dimensionally interconnected pore network of the present application can realize a loading rate of phase change material of up to 85wt% or more through capillary force and surface wetting effect, and at the same time, construct a three-dimensional rapid heat conduction channel, so as to improve the heat storage / heat release rate of the composite material. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Thermal conductivity of the carbon nanotube foam composite n-octadecane phase change material of Example 1 to Example 5 of the present application. DETAILED DESCRIPTION

[0030] In order to better explain the present application, the following will be described in detail through specific embodiments in combination with the accompanying drawings.

[0031] The microcapsule of the present application is prepared by a vacuum impregnation method to prepare a carbon nanotube foam composite phase change material, i.e. the carbon nanotube foam is placed in a vacuum environment, and the internal pores are fully impregnated with phase change material under the action of negative pressure, so as to realize the close combination of phase change material and carbon nanotube foam.

[0032] The carbon nanotube foam of the present application has the characteristics of ultra-light, high specific surface area and controllable pore structure in structure, and also has the mechanical advantages of high strength and high elasticity, and the electrically conductive and thermally conductive performance significantly better than that of traditional materials. The combination of high temperature resistance, corrosion resistance and three-dimensional interconnected pore structure provides an ideal carrier for the packaging of phase change materials. The three-dimensional interconnected pore network can realize a load rate of the phase change material of more than 85% through capillary force and surface wetting effect, and at the same time, a three-dimensional rapid heat conduction channel is constructed, so that the heat storage and release rate of the composite material is improved; the present application effectively solves the problem of core material leakage caused by volume expansion in the solid-liquid phase change process of traditional phase change materials through the unique high strength and high elasticity mechanical properties of the carbon nanotube foam, and significantly improves the cycle stability of the packaging system.

[0033] S1, surface functionalization treatment of the carbon nanotube foam: placing the carbon nanotube foam in concentrated nitric acid with a mass fraction of 65-70%, ultrasonic refluxing at 60-120℃ for several hours, washing the product with deionized water until the pH value of the filtrate reaches 7, and vacuum drying at 80℃ to ensure that the air in the pores of the carbon nanotube foam is completely discharged; this step chemically modifies the surface of the carbon nanotube foam through nitric acid oxidation.

[0034] S2, uniformly mixing excess solid phase change material with the carbon nanotube foam by dry mixing.

[0035] S3, heating the mixture obtained in step S2 in a vacuum oven to ensure that the solid phase change material is completely melted, which makes the phase change material more easily combined with the carbon nanotube foam, and the liquid phase change material can completely fill into the pore structure of the carbon nanotube foam under the driving of capillary action and pressure difference.

[0036] S4, heating in an oven to remove the remaining phase change material on the surface of the carbon nanotube foam, repeating multiple times until no phase change material is observed in the filter paper; finally, the carbon nanotube foam composite phase change microcapsule is obtained.

[0037] Example 1

[0038] The preparation method of the carbon nanotube foam composite phase change microcapsule of the present embodiment comprises the following steps:

[0039] S1, surface functionalization treatment of the carbon nanotube foam: placing the carbon nanotube foam in concentrated nitric acid with a mass fraction of 68%, ultrasonic assisted refluxing at 60℃ for 4h, washing the product with deionized water until the pH value of the filtrate reaches 7, and vacuum drying at 80℃ for 12h.

[0040] S2, uniformly mixing 1.5g of solid n-octadecane with 0.075g of carbon nanotube foam by ball milling.

[0041] S3, the mixture obtained in step S2 is heated at 100°C in a vacuum oven for 10h.

[0042] S4, the residual n-octadecane on the surface of the carbon nanotube foam is removed by heating in an oven at 100°C, repeated multiple times until no phase change material n-octadecane is observed in the filter paper. Finally, the phase change material of carbon nanotube foam composite n-octadecane is obtained.

[0043] Example 2

[0044] The preparation method of the carbon nanotube foam composite phase change microcapsule of the present example comprises the following steps:

[0045] S1, surface functionalization treatment of carbon nanotube foam: place the carbon nanotube foam in concentrated nitric acid with a mass fraction of 68%, ultrasonic-assisted reflux at 80°C for 4h, wash the product thoroughly with deionized water until the filtrate pH value reaches 7, and vacuum dry at 80°C for 16h.

[0046] S2, uniformly mix 1.5g of solid n-octadecane with 0.075g of carbon nanotube foam by mechanical grinding.

[0047] S3, heat the mixture obtained in step S2 in a vacuum oven at 100°C for 6h.

[0048] S4, the residual n-octadecane on the surface of the carbon nanotube foam is removed by heating in an oven at 100°C, repeated multiple times until no phase change material n-octadecane is observed in the filter paper. Finally, the phase change material of carbon nanotube foam composite n-octadecane is obtained.

[0049] Example 3

[0050] The preparation method of the carbon nanotube foam composite phase change microcapsule of the present example comprises the following steps:

[0051] S1, surface functionalization treatment of carbon nanotube foam: place the carbon nanotube foam in concentrated nitric acid with a mass fraction of 68%, ultrasonic-assisted reflux at 100°C for 4h, wash the product thoroughly with deionized water until the filtrate pH value reaches 7, and vacuum dry at 80°C for 12h.

[0052] S2, uniformly mix 1.5g of solid n-octadecane with 0.075g of carbon nanotube foam by mechanical grinding.

[0053] S3, heat the mixture obtained in step S2 in a vacuum oven at 80°C for 6h.

[0054] S4, the residual n-octadecane on the surface of the carbon nanotube foam is removed by heating in an oven at 80°C, repeated multiple times until no phase change material n-octadecane is observed in the filter paper; finally, the phase change material of carbon nanotube foam composite n-octadecane is obtained.

[0055] Example 4

[0056] The preparation method of the carbon nanotube foam composite phase change microcapsule of the present example comprises the following steps:

[0057] S1, surface functionalization treatment of carbon nanotube foam: place the carbon nanotube foam in concentrated nitric acid with a mass fraction of 68%, ultrasonic-assisted reflux at 120°C for 4h, wash the product thoroughly with deionized water until the pH value of the filtrate reaches 7, and vacuum dry at 80°C for 24h.

[0058] S2, uniformly mix 1.5g of solid n-octadecane with 0.075g of carbon nanotube foam by ball milling.

[0059] S3, heat the mixture obtained in step S2 in a vacuum oven at 80°C for 6h.

[0060] S4, remove the remaining n-octadecane on the surface of the carbon nanotube foam by heating in an 80°C oven, repeat multiple times until no phase change material n-octadecane is observed in the filter paper; finally obtain the carbon nanotube foam composite n-octadecane phase change material.

[0061] Example 5

[0062] The preparation method of the carbon nanotube foam composite phase change microcapsule of the present example comprises the following steps:

[0063] S1, surface functionalization treatment of carbon nanotube foam: place the carbon nanotube foam in concentrated nitric acid with a mass fraction of 68%, ultrasonic-assisted reflux at 80°C for 8h, wash the product thoroughly with deionized water until the pH value of the filtrate reaches 7, and vacuum dry at 80°C for 24h.

[0064] S2, uniformly mix 2.25g of solid n-octadecane with 0.075g of carbon nanotube foam by ball milling.

[0065] S3, heat the mixture obtained in step S2 in a vacuum oven at 80°C for 6h.

[0066] S4, remove the remaining n-octadecane on the surface of the carbon nanotube foam by heating in an 80°C oven, repeat multiple times until no phase change material n-octadecane is observed in the filter paper; finally obtain the carbon nanotube foam composite n-octadecane phase change material.

[0067] The loading rate of the carbon nanotube foam is calculated by formula (1), wherein W a represents the weight of the carbon nanotube foam after forming a composite material with the phase change material, W b is the weight of the initial carbon nanotube foam.

[0068] η = (Wa -W b ) / W a x 100% (1)

[0069] Table 1: Loading rate of carbon nanotube foam composite phase change material of n-octadecane of examples 1-5

[0070]

[0071] As can be seen from the above, the three-dimensional interconnected pore network of the application can realize a loading rate of phase change material up to 90% through capillary force and surface wetting effect, and at the same time, a three-dimensional rapid heat conduction channel is constructed, so that the heat storage / heat release rate of the composite material is improved.

[0072] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A carbon nanotube foam composite phase change microcapsule, characterized in that, The carbon nanotube foam composite phase change microcapsule includes carbon nanotube foam and a solid phase change material encapsulated in the carbon nanotube foam. The solid phase change material is selected from one of n-octadecane, fatty acid, neopentyl glycol and polyethylene glycol.

2. The method for preparing carbon nanotube foam composite phase change microcapsules according to claim 1, characterized in that, Includes the following steps: S1, the solid phase change material and the chemically modified carbon nanotube foam are uniformly mixed by dry mixing; S2, The mixture obtained in step S1 is heated in a vacuum oven to ensure that the solid phase change material is completely melted, so that the liquid phase change material can be completely filled into the pore structure of the carbon nanotube foam under the drive of capillary action and pressure difference. S3, heat in an oven to remove the remaining phase change material on the surface of the carbon nanotube foam, to obtain carbon nanotube foam composite phase change microcapsules.

3. The preparation method according to claim 2, characterized in that, In S1, the chemical modification method of the carbon nanotube foam is as follows: the carbon nanotube foam is placed in concentrated nitric acid with a mass fraction of 65-70%, ultrasonically refluxed at 60-120°C, the product is washed with deionized water until the filtrate is neutral, and then vacuum dried.

4. The preparation method according to claim 2 or 3, characterized in that, The carbon nanotube foam has an average pore size of 50-100 nm, an inner diameter of 10-20 nm, and an outer diameter of 30-50 nm.

5. The preparation method according to claim 3, characterized in that, The ultrasonic reflux time is 4-24 hours.

6. The preparation method according to claim 3, characterized in that, The drying conditions are: vacuum drying at 80℃ for 12-24 hours.

7. The preparation method according to claim 2, characterized in that, In S2, the solid phase change material is selected from one of n-octadecane, fatty acids, neopentyl glycol, and polyethylene glycol.

8. The preparation method according to claim 2, characterized in that, In S2, the mixing mass ratio of the solid phase change material to the chemically modified carbon nanotube foam is 10-30:

1.

9. The preparation method according to claim 2, characterized in that, In step S2, the heating temperature is 60-100℃, and the mixture is heated in a vacuum oven for 4-10 hours.

10. The application of the carbon nanotube foam composite phase change microcapsules as described in claim 1 or the carbon nanotube foam composite phase change microcapsules obtained by any of the preparation methods described in claims 2-9 in building materials and industrial energy storage materials.

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