A MXene-enhanced thermally conductive and wave-absorbing composite material and a preparation method thereof

Abstract

The present invention belongs to the field of thermal conductive wave absorbing composite materials, and discloses a method for preparing a MXene-enhanced thermal conductive wave absorbing composite material, wherein the thermal conductive wave absorbing skeleton is a composite material BN / MXene of boron nitride nanosheets and MXene, and the two are combined together by the electrostatic adsorption force of positive and negative charges. The continuous 3D network prepared by BNNS with a low dielectric constant provides an effective path for the transmission of heat, and the MXene with good wave absorbing performance that is uniformly dispersed but not connected is adsorbed on the basis of its skeleton, so as to prepare a dual-functional composite material with integrated thermal conductive wave absorbing performance. At the same time, the three-dimensional network structure prepared by the ice template method has certain gaps in space, which can cause multiple reflections and multiple scatterings of electromagnetic waves entering the material, increase the transmission path of electromagnetic waves, and help improve the wave absorbing performance of the composite material. The prepared composite material has good thermal conductivity and wave absorbing performance after testing.

Description

Technical Field

[0001] The present invention specifically relates to a MXene-enhanced heat-conducting and wave-absorbing composite material and a preparation method thereof, and belongs to the field of thermal interface materials and electromagnetic wave absorption. Background Art

[0002] The development trend of high integration and multifunctionality of electronic and electrical equipment has led to a continuous increase in its power, and with it comes the waste heat generated during the operation process. If this waste heat cannot be discharged from the inside of the equipment to the outside in time, the temperature of the heat-generating components will rise rapidly. This will accelerate the aging of electronic devices and affect the performance and service life of the equipment itself. Thermal interface materials such as thermal conductive silicone rubber can transfer waste heat to the radiator, and then transmit it to the outside by the radiator, thereby providing a relatively low-temperature working environment for the heat-generating components to solve the heat dissipation problem. In addition to waste heat, electronic equipment will also continuously emit electromagnetic waves to the outside world when working, causing additional electromagnetic pollution and information leakage. However, the working space inside the electronic equipment is relatively small, and most of the space has been occupied by thermal conductive silicone rubber, and it is impossible to add additional absorbing materials to eliminate electromagnetic pollution. In addition, the increase of absorbing materials will also have a negative impact on the heat dissipation of electronic equipment. Therefore, the development of integrated thermal conductive and absorbing composite materials is an effective means to solve the problems of heat dissipation and electromagnetic pollution at the same time. However, the preparation of integrated thermal conductive and wave absorbing composite materials is not simply achieved by adding thermal conductive and wave absorbing fillers into a polymer matrix. This is because there is a contradiction in the design between the thermal conductive and wave absorbing functions: to achieve the thermal conductive function, the filler must have strong continuity inside the polymer and a continuous thermal conductive pathway; while to achieve the wave absorbing performance, the filler must be evenly dispersed inside the polymer but isolated from each other. Once the fillers are connected, they will produce a shielding effect rather than a wave absorbing effect.

[0003] In order to resolve this contradiction, the present invention selects BN without wave absorbing properties as the main thermal conductive skeleton to exert its excellent thermal conductivity. After chemical treatment, it shows positive charge, and is combined with MXene, which has its own electronegativity, through the electrostatic adsorption force of positive and negative charges. By controlling the amount between the two, the small-particle MXene is adsorbed on the surface of the large-particle BN to prepare a BN / MXene composite filler. The thermal conductive wave absorbing skeleton prepared by the ice template method of this composite filler achieves the effect of continuous thermal conductive filler and isolated wave absorbing filler from each other, thereby achieving excellent thermal conductivity and wave absorbing properties. The process of preparing MXene involves a chemical etching process, which is bound to produce a large number of defects and active functional groups on the surface of the material. Under the action of an external electromagnetic field, these areas will provide active sites for the aggregation of charges, produce dipole polarization and interface polarization phenomena, and improve the wave absorbing performance of the material. In addition, MXene itself also has good thermal conductivity, so the addition of MXene does not reduce the thermal conductivity of the composite material, but will improve the thermal conductivity of the composite material. Summary of the invention

[0004] The present invention discloses a MXene-enhanced heat-conducting and wave-absorbing composite material and a preparation method thereof. The present invention selects a continuous 3D network prepared by BNNS with a low dielectric constant to provide an effective path for heat transmission, and adsorbs uniformly dispersed but unconnected MXene with good wave-absorbing performance on the basis of its skeleton, so as to prepare a dual-functional composite material with integrated heat conduction and wave-absorbing performance. At the same time, the three-dimensional network structure prepared by the ice template method has certain gaps in space, which can cause multiple reflections and multiple scatterings of electromagnetic waves entering the material, increase the transmission path of electromagnetic waves, and help improve the wave-absorbing performance of the composite material. The prepared composite material has good thermal conductivity and wave-absorbing performance after testing.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The thermally conductive and absorbing filler in the thermally conductive and absorbing composite material is boron nitride nanosheets (BNNS) and MXene, which are combined together by the electrostatic adsorption force of positive and negative charges to obtain BN / MXene thermally conductive and absorbing filler. The thermally conductive and absorbing filler is used to prepare a directional and arranged thermally conductive and absorbing skeleton in the vertical direction using an ice template method, and then the thermally conductive and absorbing composite material is prepared by pouring liquid silicone rubber.

[0007] The specific preparation steps are:

[0008] (1) Preparation of MXene: Ti 3 AlC 2 The MAX phase is placed in a hydrochloric acid solution of LiF to etch away the Al atomic layer to obtain MXene. The surface of the prepared MXene will have negatively charged functional groups such as F-, OH- and O-, so the prepared MXene is negatively charged; the concentration of the hydrochloric acid solution is 9 mol / L, and the concentration of lithium fluoride in the hydrochloric acid solution is 2g / 40mL; lithium fluoride and Ti 3 AlC 2 The mass ratio of MAX phase is 1:1; the etching conditions are: continuous stirring at 40°C for 36 hours.

[0009] (2) Preparation of BNNS: Hexagonal boron nitride with a diameter of (10-30) μm was placed in a ball mill at a ball-to-material mass ratio of (10-40):1, the ball milling speed was (300-500) r / min, and the ball milling time was (24-48) h. The ball-milled BNNS was centrifuged and then placed in an oven for drying to obtain BNNS;

[0010] (3) Preparation of BNNS with positive charge on the surface: The BNNS prepared in step (2) is placed in a hexadecyltrimethylammonium bromide solution with a concentration of (1-10) g / L and ultrasonically treated for (2-4) h, and then stirred for (10-30) h to make the surface of the BNNS positively charged, and then dried for use to obtain C-BNNS;

[0011] (4) Preparation of BN / MXene functional filler: C-BNNS and MXene are prepared into a suspension at a mass ratio of 20:(0.5-5), and then placed on a stirring platform and stirred at (100-300) rpm for (10-60) min, and then allowed to stand for 24 hours. Since the two have different positive and negative charges, they will be combined together by electrostatic adsorption during the standing process. The precipitate is repeatedly washed with water and centrifuged, and then dried at 50°C for later use, to obtain BN / MXene functional filler;

[0012] (5) Preparation of thermal conductive wave absorbing skeleton: The prepared BN / MXene functional filler and xanthan gum are prepared into a water suspension, the concentration of xanthan gum is (0.02-5) g / L, and the concentration of filler is (10-50) g / L, and the prepared suspension is placed on a directional freezing platform. Since the cold source is at the bottom, the ice crystals will grow vertically from the bottom to the top, so that the filler is squeezed into a vertical thermal conductive wave absorbing skeleton ice structure during the growth of ice crystals from bottom to top through the ice template method. This ice structure is then frozen by a freeze dryer at (-20--30) ° C for (2-5) days to remove the ice crystals, and a vertical thermal conductive wave absorbing skeleton can be obtained;

[0013] (6) Preparation of heat-conducting and wave-absorbing composite materials: The heat-conducting and wave-absorbing skeleton is poured into liquid silicone rubber to fill the gaps left by the evaporated ice crystals, and then cured to obtain the heat-conducting and wave-absorbing composite materials. The mass ratio of the components of the liquid silicone rubber, vinyl-terminated silicone oil, hydrogen-containing silicone oil, inhibitor and accelerator is 100: (10-20): (2-10): (1-10).

[0014] The relationship between the usage of the heat-conducting and wave-absorbing skeleton and the liquid silicone rubber is close to the mass ratio of the filler to water in the configured suspension.

[0015] Furthermore, as a preference, in the preparation of BN / MXene functional fillers, C-BNNS and MXene are mixed in a mass ratio of 20:0.75, and the optimal comprehensive performance of thermal conductivity and wave absorption can be achieved with a relatively small amount of MXene.

[0016] Compared with the prior art, the present invention has the following excellent effects:

[0017] In the preparation of BN / MXene functional fillers in the present invention, BNNS and MXene are combined through the electrostatic adsorption force of positive and negative charges, which reduces the interfacial thermal resistance between the two and improves the thermal conductivity. In addition, the method of first combining BNNS and MXene through the electrostatic adsorption force of positive and negative charges effectively isolates MXene by using BNNS, reduces the agglomeration of MXene, and the mutual isolation between MXene significantly improves the wave absorption performance of the composite material. In addition, by optimizing the amount of BN and MXene, matching the ice template method, the improvement of the comprehensive performance of wave absorption performance and thermal conductivity is guaranteed.

[0018] The heat-conducting and wave-absorbing composite material prepared by the present invention has good heat-conducting and wave-absorbing properties, wherein the heat-conducting properties are mainly derived from the BN / MXene heat-conducting path constructed by the ice template method and the good heat-conducting properties of the filler itself. In addition, the BNNS and MXene combined by the positive and negative charge adsorption help to reduce the problem of mismatch between the interfacial thermal resistance and phonon vibration between the fillers, and further improve the heat-conducting properties. The main source of the wave-absorbing properties is that the three-dimensional network structure prepared by the ice template method has certain gaps in space, which can cause multiple reflections and multiple scattering of electromagnetic waves entering the material, increase the transmission path of electromagnetic waves, and help improve the wave-absorbing properties of the composite material. The wave-absorbing properties of the composite material are mainly attributed to the multiple reflections of the three-dimensional structure, the conductive loss of MXene, the polarization relaxation, and the interface polarization loss generated at the heterogeneous interfaces of the composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Zeta potential diagrams of MXene, C-BNNS and BN / MXene;

[0020] Figure 2 This is a SEM image of the MXene-enhanced thermally conductive and wave-absorbing composite material prepared in Example 1;

[0021] Figure 3 This is a graph showing the wave absorption performance of the MXene-enhanced thermally conductive and wave absorbing composite material prepared in Example 1;

[0022] Figure 4 This is a graph showing the wave absorption performance of the MXene-enhanced thermally conductive and wave absorbing composite material prepared in Example 2;

[0023] Figure 5 This is a graph showing the wave absorption performance of the composite material prepared in Comparative Example 1;

[0024] Figure 6 This is a graph showing the wave absorption performance of the composite material prepared in Comparative Example 2;

[0025] Figure 7 This is a graph showing the wave absorption performance of the composite material prepared in Comparative Example 3;

[0026] Figure 8 This is a graph showing the wave absorption performance of the composite material prepared in Comparative Example 4;

[0027] Fig. 9 This is a graph showing the wave absorption performance of the material prepared in Comparative Example 5;

[0028] Fig.10 This is a graph showing the microwave absorption performance of the material prepared in Comparative Example 6. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail in conjunction with the embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] Example 1

[0031] The preparation method comprises the following steps:

[0032] 1) First, prepare 40 mL of 9 mol / L concentrated hydrochloric acid in a 100 mL polytetrafluoroethylene container, then weigh 2 g of lithium fluoride and slowly add it to the above solution, stirring for 30 min; weigh 2 g of Ti 3 AlC 2 The MAX phase was slowly added to the solution, and then the reaction mixture was placed in a 40°C water bath and stirred continuously for 36 hours. After the reaction was completed, it was repeatedly washed with water until the solution was neutral, and then the reaction mixture was placed in an ultrasonic treatment for 30 minutes. The reactants were then loaded into centrifuge tubes in batches, centrifuged at 3500 rpm for 20 minutes, and the supernatant was taken. Repeat the above steps until the supernatant was clear, and the supernatant was concentrated by centrifugation at 11000 rpm for 40 minutes, and then placed in a sample bottle filled with argon inert gas protection, and a sample was taken to test the concentration of the MXene solution;

[0033] 2) Weigh 4g BN and 80g stainless steel balls and place them in a ball mill for ball milling. The ball mill speed is set to 500r / min and the ball milling time is 24h. The treated BNNS is filtered and placed in a 50℃ oven for 24h for use. Prepare 500mL of 2g / L hexadecyltrimethylammonium bromide (CTAB) solution, add 4g BNNS to it, ultrasonically treat for 2h, and then stir for 20h to make the surface of BNNS positively charged. Centrifuge the treated BNNS and place it at 50℃ for drying to obtain C-BNNS. Weigh an appropriate amount of treated C-BNNS, and prepare a C-BNNS / MXene suspension with a mass ratio of C-BNNS:MXene of 20:0.75. Place it on a stirring platform and stir at 100rpm for 30min, then let it stand for 24h. Wash the precipitate repeatedly with water and centrifuge it 4 times, then place it at 50℃ for drying to obtain BN / MXene functional filler;

[0034] 3) The prepared BN / MXene functional filler and xanthan gum are configured into a water suspension, the concentration of xanthan gum is 0.05 g / L, and the concentration of filler is 20.75 g / L. The configured suspension is placed on a homemade directional freezing platform to prepare a vertical heat-conducting and wave-absorbing skeleton ice structure. The ice structure is then freeze-dried in a freeze dryer at (-20 to -30) ° C for 3 days to remove the ice crystals therein, and a vertical heat-conducting and wave-absorbing skeleton can be obtained;

[0035] 4) Vinyl-terminated silicone oil, hydrogen-containing silicone oil, and addition-type silicone rubber platinum inhibitor (delay agent) XY-308 are weighed at a mass ratio of 100:10:5, and then vacuum degassing and mixing is performed at a speed of 800 rpm. After uniform mixing, platinum catalyst is weighed at a mass ratio (vinyl-terminated silicone oil: platinum catalyst = 100:2) and vacuum degassing and mixing is performed at a speed of 1500 rpm. The heat-conducting and wave-absorbing skeleton prepared in step 3) is immersed in the prepared silicone rubber solution, heated to 80°C, and cured for 20 minutes;

[0036] 5) The cured composite material is sliced ​​into thin sheets with a thickness of 1.8 mm by a slicer, thereby obtaining a MXene-reinforced thermal conductive and wave absorbing composite material.

[0037] The above heat-conducting and wave-absorbing composite material was made into a 3cm diameter disc through a mold. Its thermal conductivity was tested using a Hotdisk thermal conductivity tester according to ISO 22007-2 standard. Six samples were tested and the average value was 0.83W / m·K, which was 315% higher than that of pure silicone rubber (thermal conductivity of 0.20W / m·K). Its wave-absorbing performance was tested by a vector network analyzer. The effective absorption bandwidth (R L≤-10dB) is 4.13GHz. This thermally conductive and absorbing composite material exhibits excellent thermal conductivity and wave absorption properties, and can be used in the field of electronic devices that require both thermal conductivity and wave absorption. The good thermal conductivity of the composite material mainly comes from the BN / MXene three-dimensional thermal conductive skeleton pathway constructed by the ice template method and the good thermal conductivity of the filler itself. In addition, the BNNS and MXene combined by the electrostatic adsorption force of positive and negative charges reduce the problem of interfacial thermal resistance and phonon vibration mismatch between fillers. The wave absorption performance of the composite material with good wave absorption performance is mainly attributed to the multiple reflections generated by the three-dimensional structure prepared by the ice template method, the conductive loss of MXene, polarization relaxation, and the interface polarization loss generated at the heterogeneous interfaces of the composite material.

[0038] Example 2

[0039] The preparation method comprises the following steps:

[0040] 1) First, prepare 40 mL of 9 mol / L concentrated hydrochloric acid in a 100 mL polytetrafluoroethylene container, then weigh 2 g of lithium fluoride and slowly add it to the above solution, stirring for 30 min; weigh 2 g of Ti 3 AlC 2 The MAX phase was slowly added to the solution, and then the reaction mixture was placed in a 40°C water bath and stirred continuously for 36 hours. After the reaction was completed, it was repeatedly washed with water until the solution was neutral, and then the reaction mixture was placed in an ultrasonic treatment for 30 minutes. The reactants were then loaded into centrifuge tubes in batches, centrifuged at 3500 rpm for 20 minutes, and the supernatant was taken. Repeat the above steps until the supernatant was clear, and the supernatant was concentrated by centrifugation at 11000 rpm for 40 minutes, and then placed in a sample bottle filled with argon inert gas protection, and a sample was taken to test the concentration of the MXene solution;

[0041] 2) Weigh 4g BN and 80g stainless steel balls and place them in a ball mill for ball milling. The ball mill speed is set to 400r / min and the ball milling time is 36h. The treated BNNS is filtered and placed in a 50℃ oven for 24h for use. Prepare 500mL of 4g / L hexadecyltrimethylammonium bromide (CTAB) solution, add 4g BNNS to it, ultrasonically treat for 2h, and then stir for 20h to make the surface of BNNS positively charged. Centrifuge the treated BNNS and place it at 50℃ for drying to obtain C-BNNS. Weigh an appropriate amount of treated C-BNNS, and prepare a C-BNNS / MXene suspension with a mass ratio of C-BNNS:MXene of 20:0.75. Place it on a stirring platform and stir at 100rpm for 30min, then let it stand for 24h. Wash the precipitate repeatedly with water and centrifuge it 4 times, then place it at 50℃ for drying to obtain BN / MXene functional filler;

[0042] 3) The prepared BN / MXene functional filler and xanthan gum are configured into a water suspension, the concentration of xanthan gum is 0.1 g / L, and the concentration of filler is 20.75 g / L. The configured suspension is placed on a homemade directional freezing platform to prepare a vertical heat-conducting and wave-absorbing skeleton ice structure. The ice structure is then freeze-dried in a freeze dryer at (-20 to -30) ° C for 3 days to remove the ice crystals therein, thereby obtaining a vertical heat-conducting and wave-absorbing skeleton;

[0043] 4) Vinyl-terminated silicone oil, hydrogen-containing silicone oil, and addition-type silicone rubber platinum inhibitor (delay agent) XY-308 are weighed at a mass ratio of 100:10:5, and then vacuum degassing and mixing is performed at a speed of 800 rpm. After uniform mixing, platinum catalyst is weighed at a mass ratio (vinyl-terminated silicone oil: platinum catalyst = 100:2) and vacuum degassing and mixing is performed at a speed of 1500 rpm. The heat-conducting and wave-absorbing skeleton prepared in step 3) is immersed in the prepared silicone rubber solution, heated to 80°C, and cured for 20 minutes;

[0044] 5) The cured composite material is sliced ​​into thin sheets with a thickness of 1.8 mm by a slicer, thereby obtaining a MXene-reinforced thermal conductive and wave absorbing composite material.

[0045] The above heat-conducting and wave-absorbing composite material was made into a 3cm diameter disc through a mold. Its thermal conductivity was tested using a Hotdisk thermal conductivity tester according to ISO 22007-2 standard. Six samples were tested and the average value was 0.81W / m·K, which was 305% higher than that of pure silicone rubber (thermal conductivity of 0.20W / m·K). Its wave-absorbing performance was tested by a vector network analyzer. The effective absorption bandwidth (R L ≤-10dB) is 4GHz. This thermal conductive and wave absorbing composite material exhibits excellent thermal conductivity and wave absorbing properties and can be used in the field of electronic devices that require both thermal conductivity and wave absorbing.

[0046] Comparative Example 1

[0047] The difference between this comparative example 1 and example 1 is that the BN is not treated.

[0048] 1) First, prepare 40 mL of 9 mol / L concentrated hydrochloric acid in a 100 mL polytetrafluoroethylene container, then weigh 2 g of lithium fluoride and slowly add it to the above solution, stirring for 30 min; weigh 2 g of Ti 3 AlC 2The MAX phase was slowly added to the solution, and then the reaction mixture was placed in a 40°C water bath and stirred continuously for 36 hours. After the reaction was completed, it was repeatedly washed with water until the solution was neutral, and then the reaction mixture was placed in an ultrasonic treatment for 30 minutes. The reactants were then loaded into centrifuge tubes in batches, centrifuged at 3500 rpm for 20 minutes, and the supernatant was taken. Repeat the above steps until the supernatant was clear, and the supernatant was concentrated by centrifugation at 11000 rpm for 40 minutes, and then placed in a sample bottle filled with argon inert gas protection, and a sample was taken to test the concentration of the MXene solution;

[0049] 2) Weigh 4g BN and 80g stainless steel balls and place them in a ball mill for ball milling. The ball milling speed is set to 500r / min and the ball milling time is 24h to directly obtain BNNS. Weigh BNNS and prepare a suspension with a mass ratio of BNNS:MXene of 20:0.75. Place it on a stirring platform and stir at 100rpm for 30min, then let it stand for 24h. Wash the precipitate repeatedly with water and centrifuge it 4 times, then place it at 50℃ for drying for later use to obtain BN / MXene composite filler;

[0050] 3) The BN / MXene composite filler and xanthan gum were prepared into a water suspension, the concentration of xanthan gum was 0.05 g / L, and the concentration of the filler was 20.75 g / L. The prepared suspension was placed on a homemade directional freezing platform to prepare a vertical heat-conducting and wave-absorbing skeleton ice structure. The ice structure was then cold-dried in a freeze dryer at (-20 to -30) ° C for 3 days to remove the ice crystals therein, and a vertical heat-conducting and wave-absorbing skeleton was obtained;

[0051] 4) Vinyl-terminated silicone oil, hydrogen-containing silicone oil, and addition-type silicone rubber platinum inhibitor (delay agent) XY-308 are weighed at a mass ratio of 100:10:5, and then vacuum degassing and mixing is performed at a speed of 800 rpm. After uniform mixing, platinum catalyst is weighed at a mass ratio (vinyl-terminated silicone oil: platinum catalyst = 100:2) and vacuum degassing and mixing is performed at a speed of 1500 rpm. The heat-conducting and wave-absorbing skeleton prepared in step 3) is immersed in the prepared silicone rubber solution, heated to 80°C, and cured for 20 minutes;

[0052] 5) The cured composite material is sliced ​​into thin sheets with a thickness of 1.8 mm using a slicer, thereby obtaining a thermal conductive and wave absorbing composite material.

[0053] The above heat-conducting and wave-absorbing composite material was made into a 3cm diameter disc through a mold. Its thermal conductivity was tested using a Hotdisk thermal conductivity tester according to ISO 22007-2 standard. Six samples were tested and the average value was 0.75W / m·K, which was only 275% higher than that of pure silicone rubber (thermal conductivity of 0.20W / m·K). Its wave-absorbing performance was tested by a vector network analyzer. The effective absorption bandwidth (R L ≤-10dB) is 2.6GHz. This is mainly because BNNS and MXene are not combined through the electrostatic adsorption force of positive and negative charges. Although the ice template method is also used to prepare the thermal conductive and absorbing skeleton, the direct binding force of the filler is poor, resulting in the introduction of interfacial thermal resistance, thereby reducing the thermal conductivity. In terms of absorbing performance, the combination of positive and negative charges that attract each other not only solves the problem of binding force. At the same time, an unexpected result is produced: BNNS and MXene are first combined through the electrostatic adsorption force of positive and negative charges, and the MXene is effectively isolated by BNNS. This isolation effect is beneficial to the improvement of absorbing performance. This comparative example is not combined through the positive and negative charge adsorption force, resulting in partial agglomeration of MXene in the system, which cannot isolate the MXene from each other, and thus greatly reduces the absorbing performance of the composite material.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 1 is that BNNS and MXene are directly mixed into the vinyl silicone rubber system by a simple blending method to directly prepare a composite material. In Example 1 and Comparative Example 1, the gaps finally filled by the vinyl silicone rubber are the gaps remaining after the water freezes and sublimates, and the density of the liquid vinyl silicone rubber is about 1.1 g / cm 3 , which is basically close to the density of water, so the mass ratio of the filler in Comparative Example 2 is weighed according to the mass ratio of the filler in the suspension.

[0056] The preparation method of the composite material comprises the following steps:

[0057] 1) First, prepare 40 mL of 9 mol / L concentrated hydrochloric acid in a 100 mL polytetrafluoroethylene container, then weigh 2 g of lithium fluoride and slowly add it to the above solution, stirring for 30 min; weigh 2 g of Ti 3 AlC 2The MAX phase was slowly added to the solution, and then the reaction mixture was placed in a 40°C water bath and stirred continuously for 36 hours. After the reaction was completed, it was repeatedly washed with water until the solution was neutral, and then the reaction mixture was placed in an ultrasonic treatment for 30 minutes. The reactants were then loaded into centrifuge tubes in batches, centrifuged at 3500 rpm for 20 minutes, and the supernatant was taken. Repeat the above steps until the supernatant was clear, and the supernatant was concentrated by centrifugation at 11000 rpm for 40 minutes. After freeze-drying, MXene powder was prepared for use;

[0058] 2) Weigh 4 g of BN and 80 g of stainless steel balls and place them in a ball mill for ball milling. The ball milling speed is set to 500 r / min and the ball milling time is 24 h to directly obtain BNNS.

[0059] 3) vinyl-terminated silicone oil, hydrogen-containing silicone oil, addition silicone rubber platinum inhibitor (delay agent) XY-308, MXene (0.75% of the total mass) and BNNS were weighed in proportion (20% of the total mass) and then vacuum degassed and mixed at a speed of 800 rpm. After mixing evenly, platinum catalyst was weighed in proportion and vacuum degassed and mixed at a speed of 1500 rpm;

[0060] 4) The mixed slurry is coated with a coating machine, and the coating thickness is 1.8 mm;

[0061] 5) The composite material is cured at 80° C. for 20 minutes.

[0062] The above heat-conducting and wave-absorbing composite material was made into a 3cm diameter disc through a mold. Its thermal conductivity was tested using a Hotdisk thermal conductivity tester according to ISO 22007-2 standard. Six samples were tested and the average value was 0.28W / m·K, which was only 40% higher than that of pure silicone rubber (thermal conductivity of 0.20W / m·K). Its wave-absorbing performance was tested by a vector network analyzer. The effective absorption bandwidth (R L≤-10dB) is 1.4GHz. The significant decrease in thermal conductivity mainly comes from two aspects: 1) The simple blending method causes the fillers to be arranged in a disorderly manner inside the matrix, and the fillers cannot fully exert their thermal conductivity in the system and cannot form an effective thermal conduction path; 2) BNNS and MXene are not combined through the electrostatic adsorption force of positive and negative charges, and the interface thermal resistance is introduced between the two, thereby reducing the thermal conductivity. The decrease in wave absorption performance comes from the following two aspects: 1) The ice template method is not used to prepare a special three-dimensional structure, which reduces the gaps inside the composite material and prevents the incoming electromagnetic waves from producing multiple emission effects; 2) Simple blending causes MXene to be unevenly dispersed throughout the system, which may form a partial agglomeration phenomenon, so that the MXenes cannot be isolated from each other, resulting in a significant decrease in the wave absorption performance of the composite material.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 1 is that the mass ratio of BNNS to MXene is reduced from 20:0.75 to 20:0.5.

[0065] The preparation method comprises the following steps:

[0066] 1) First, prepare 40 mL of 9 mol / L concentrated hydrochloric acid in a 100 mL polytetrafluoroethylene container, then weigh 2 g of lithium fluoride and slowly add it to the above solution, stirring for 30 min; weigh 2 g of Ti 3 AlC 2 The MAX phase was slowly added to the solution, and then the reaction mixture was placed in a 40°C water bath and stirred continuously for 36 hours. After the reaction was completed, it was repeatedly washed with water until the solution was neutral, and then the reaction mixture was placed in an ultrasonic treatment for 30 minutes. The reactants were then loaded into centrifuge tubes in batches, centrifuged at 3500 rpm for 20 minutes, and the supernatant was taken. Repeat the above steps until the supernatant was clear, and the supernatant was concentrated by centrifugation at 11000 rpm for 40 minutes, and then placed in a sample bottle filled with argon inert gas protection, and a sample was taken to test the concentration of the MXene solution;

[0067] 2) Weigh 4g BN and 80g stainless steel balls and place them in a ball mill for ball milling. The ball mill speed is set to 500r / min and the ball milling time is 24h. The treated BNNS is filtered and placed in a 50℃ oven for 24h for use. Prepare 500mL of 2g / L hexadecyltrimethylammonium bromide (CTAB) solution, add 4g BNNS to it, ultrasonically treat for 2h, and then stir for 20h to make the surface of BNNS positively charged. Centrifuge the treated BNNS and place it at 50℃ for drying to obtain C-BNNS. Weigh an appropriate amount of treated C-BNNS, and prepare a C-BNNS / MXene suspension with a mass ratio of C-BNNS:MXene of 20:0.5. Place it on a stirring platform and stir at 100rpm for 30min, then let it stand for 24h. Wash the precipitate repeatedly with water and centrifuge it 4 times, then place it at 50℃ for drying to obtain BN / MXene functional filler;

[0068] 3) The prepared BN / MXene functional filler and xanthan gum are configured into a water suspension, the concentration of xanthan gum is 0.05 g / L, and the concentration of the filler is 20.5 g / L. The configured suspension is placed on a homemade directional freezing platform to prepare a vertical heat-conducting and wave-absorbing skeleton ice structure. The ice structure is then cold-dried at (-20 to -30) ° C for 3 days in a freeze dryer to remove ice crystals therein, thereby obtaining a vertical heat-conducting and wave-absorbing skeleton;

[0069] 4) Vinyl-terminated silicone oil, hydrogen-containing silicone oil, and addition-type silicone rubber platinum inhibitor (delay agent) XY-308 are weighed at a mass ratio of 100:10:5, and then vacuum degassing and mixing is performed at a speed of 800 rpm. After uniform mixing, platinum catalyst is weighed at a mass ratio (vinyl-terminated silicone oil: platinum catalyst = 100:2) and vacuum degassing and mixing is performed at a speed of 1500 rpm. The heat-conducting and wave-absorbing skeleton prepared in step 3) is immersed in the prepared silicone rubber solution, heated to 80°C, and cured for 20 minutes;

[0070] 5) The cured composite material is sliced ​​into thin sheets with a thickness of 1.8 mm using a slicer, thereby obtaining a thermal conductive and wave absorbing composite material.

[0071] The above heat-conducting and wave-absorbing composite material was made into a 3cm diameter disc through a mold, and its thermal conductivity was tested using a Hotdisk thermal conductivity tester according to ISO 22007-2 standard. Six samples were tested and the average value was 0.77W / m·K, which was only 285% higher than that of pure silicone rubber (thermal conductivity of 0.20W / m·K). Its wave-absorbing performance was tested by a vector network analyzer, and the effective absorption bandwidth (RL≤-10dB) was 0GHz at a thickness of 1.8mm, that is, it had no wave-absorbing performance.

[0072] Comparative Example 4

[0073] The difference between Comparative Example 4 and Example 1 is that the mass ratio of BNNS to MXene is increased from 20:0.75 to 20:1.

[0074] The preparation method comprises the following steps:

[0075] 1) First, prepare 40 mL of 9 mol / L concentrated hydrochloric acid in a 100 mL polytetrafluoroethylene container, then weigh 2 g of lithium fluoride and slowly add it to the above solution, stirring for 30 min; weigh 2 g of Ti 3 AlC 2 The MAX phase was slowly added to the solution, and then the reaction mixture was placed in a 40°C water bath and stirred continuously for 36 hours. After the reaction was completed, it was repeatedly washed with water until the solution was neutral, and then the reaction mixture was placed in an ultrasonic treatment for 30 minutes. The reactants were then loaded into centrifuge tubes in batches, centrifuged at 3500 rpm for 20 minutes, and the supernatant was taken. Repeat the above steps until the supernatant was clear, and the supernatant was concentrated by centrifugation at 11000 rpm for 40 minutes, and then placed in a sample bottle filled with argon inert gas protection, and a sample was taken to test the concentration of the MXene solution;

[0076] 2) Weigh 4g BN and 80g stainless steel balls and place them in a ball mill for ball milling. The ball mill speed is set to 500r / min and the ball milling time is 24h. The treated BNNS is filtered and placed in a 50℃ oven for 24h for use. Prepare 500mL of 2g / L hexadecyltrimethylammonium bromide (CTAB) solution, add 4g BNNS to it, ultrasonically treat for 2h, and then stir for 20h to make the surface of BNNS positively charged. Centrifuge the treated BNNS and place it at 50℃ for drying to obtain C-BNNS. Weigh an appropriate amount of treated C-BNNS, and prepare a C-BNNS / MXene suspension with a mass ratio of C-BNNS:MXene of 20:1. Place it on a stirring platform and stir at 100rpm for 30min, then let it stand for 24h. Wash the precipitate repeatedly with water and centrifuge it 4 times, then place it at 50℃ for drying to obtain BN / MXene functional filler;

[0077] 3) The prepared BN / MXene functional filler and xanthan gum are configured into a water suspension, the concentration of xanthan gum is 0.05 g / L, and the concentration of the filler is 21 g / L. The configured suspension is placed on a homemade directional freezing platform to prepare a vertical heat-conducting and wave-absorbing skeleton ice structure. The ice structure is then cold-dried at (-20 to -30) ° C for 3 days in a freeze dryer to remove ice crystals, thereby obtaining a vertical heat-conducting and wave-absorbing skeleton;

[0078] 4) Vinyl-terminated silicone oil, hydrogen-containing silicone oil, and addition-type silicone rubber platinum inhibitor (delay agent) XY-308 are weighed at a mass ratio of 100:10:5, and then vacuum degassing and mixing is performed at a speed of 800 rpm. After uniform mixing, platinum catalyst is weighed at a mass ratio (vinyl-terminated silicone oil: platinum catalyst = 100:2) and vacuum degassing and mixing is performed at a speed of 1500 rpm. The heat-conducting and wave-absorbing skeleton prepared in step 3) is immersed in the prepared silicone rubber solution, heated to 80°C, and cured for 20 minutes;

[0079] 5) The cured composite material is sliced ​​into thin sheets with a thickness of 1.8 mm using a slicer, thereby obtaining a thermal conductive and wave absorbing composite material.

[0080] The above-mentioned thermal conductive and wave-absorbing composite material was made into a disc with a diameter of 3 cm through a mold. The thermal conductivity was tested using a Hotdisk thermal conductivity tester according to the ISO 22007-2 standard. Six samples were tested and the average value was 0.91 W / m·K, which was only 355% higher than that of pure silicone rubber (thermal conductivity of 0.20 W / m·K). The wave-absorbing performance was tested by a vector network analyzer. The effective absorption bandwidth (RL≤-10dB) was only 2.36 GHz at a thickness of 1.8 mm, and the wave-absorbing performance was greatly reduced. With the increase in the amount of MXene, the thermal conductivity increased, while the wave-absorbing performance decreased. Considering the thermal conductivity and wave-absorbing performance, the mass ratio of BNNS to MXene of 20:0.75 is the preferred result. This may be because as the amount of MXene increases, the MXenes are connected to each other to form a conductive path, but the wave-absorbing performance decreases with the increase in the amount.

[0081] Comparative Example 5

[0082] This comparative example 5 is a thermal conductive and wave absorbing material prepared using MXene alone.

[0083] The preparation method comprises the following steps:

[0084] 1) First, prepare 40mL of 9mol / L concentrated hydrochloric acid in a 100mL polytetrafluoroethylene container, then weigh 2g of lithium fluoride and slowly add it to the above solution, and start stirring for 30min; weigh 2g of Ti3AlC2 MAX phase and slowly add it to the solution, then place the reaction mixture in a 40°C water bath and stir continuously for 36h. After the reaction is completed, wash repeatedly with water until the solution is neutral, and then place the reaction mixture in ultrasound for 30min. Then load the reactants into centrifuge tubes in batches, centrifuge at 3500rpm for 20min, and take the supernatant. Repeat the above steps until the supernatant is clear, place the supernatant at 11000rpm for 40min to concentrate the supernatant, put it into a sample bottle filled with argon inert gas protection, and take a sample to test the concentration of the MXene solution;

[0085] 2) Prepare a suspension of 20.75 g / L MXene and 0.05 g / L xanthan gum, place the prepared suspension on a homemade directional freezing platform to prepare a vertical heat-conducting and wave-absorbing skeleton ice structure, and then use a freeze dryer to dry the ice structure at (-20 to -30) °C for 3 days to remove the ice crystals, thereby obtaining a vertical heat-conducting and wave-absorbing skeleton;

[0086] 3) Vinyl-terminated silicone oil, hydrogen-containing silicone oil, and addition-type silicone rubber platinum inhibitor (delay agent) XY-308 are weighed at a mass ratio of 100:10:5, and then vacuum degassing and mixing is performed at a speed of 800 rpm. After uniform mixing, platinum catalyst is weighed at a mass ratio (vinyl-terminated silicone oil: platinum catalyst = 100:2) and vacuum degassing and mixing is performed at a speed of 1500 rpm. The heat-conducting and wave-absorbing skeleton prepared in step 2) is immersed in the prepared silicone rubber solution, heated to 80°C, and cured for 20 minutes;

[0087] 4) The cured composite material is sliced ​​into thin sheets with a thickness of 1.8 mm by a slicer, thereby obtaining a thermal conductive and wave absorbing composite material.

[0088] The above heat-conducting and wave-absorbing composite material was made into a 3cm diameter disc through a mold, and its thermal conductivity was tested using a Hotdisk thermal conductivity tester according to ISO 22007-2 standard. Six samples were tested and the average value was 0.31W / m·K, which was only 55% higher than that of pure silicone rubber (thermal conductivity of 0.20W / m·K). The wave-absorbing performance was tested by a vector network analyzer, and the effective absorption bandwidth (RL≤-10dB) was only 0.94GHz at a thickness of 1.8mm, and the wave-absorbing performance was greatly reduced.

[0089] Comparative Example 6

[0090] This comparative example is a thermal conductive wave absorbing material prepared using BNNS alone. The preparation method includes the following steps:

[0091] 1) Weigh 4 g BN and 80 g stainless steel balls and place them in a ball mill for ball milling. The ball milling speed is set to 500 r / min and the ball milling time is 24 h to obtain BNNS;

[0092] 2) The prepared BNNS and xanthan gum are configured into a water suspension, the concentration of xanthan gum is 0.05 g / L, and the concentration of filler is 20.75 g / L. The configured suspension is placed on a homemade directional freezing platform to prepare a vertical heat-conducting and wave-absorbing skeleton ice structure. The ice structure is then cold-dried at (-20 to -30) ° C for 3 days in a freeze dryer to remove ice crystals therein, thereby obtaining a vertical heat-conducting and wave-absorbing skeleton;

[0093] 3) Vinyl-terminated silicone oil, hydrogen-containing silicone oil, and addition-type silicone rubber platinum inhibitor (delay agent) XY-308 are weighed at a mass ratio of 100:10:5, and then vacuum degassing and mixing is performed at a speed of 800 rpm. After uniform mixing, platinum catalyst is weighed at a mass ratio (vinyl-terminated silicone oil: platinum catalyst = 100:2) and vacuum degassing and mixing is performed at a speed of 1500 rpm. The thermal conductive skeleton prepared in step 2) is immersed in the prepared silicone rubber solution, heated to 80°C, and cured for 20 minutes;

[0094] 4) The cured composite material is sliced ​​into thin slices with a thickness of 1.8 mm by a slicer, thereby obtaining a thermally conductive composite material.

[0095] The above heat-conducting and wave-absorbing composite material was made into a 3cm diameter disc through a mold, and its thermal conductivity was tested using a Hotdisk thermal conductivity tester according to ISO 22007-2 standard. Six samples were tested and the average value was 0.45W / m·K, which was only 125% higher than that of pure silicone rubber (thermal conductivity of 0.20W / m·K), and the thermal conductivity was greatly reduced. The wave-absorbing performance was tested by a vector network analyzer, and the reflection loss at a thickness of 1.8mm was 0dB, and there was no region of RL≤-10dB, that is, it had no wave-absorbing performance.

Claims

1. A method for preparing a MXene-enhanced thermally conductive and wave-absorbing composite material. Features: The MXene-enhanced heat-conducting and wave-absorbing composite material is prepared by using the ice template method to prepare a directional heat-conducting and wave-absorbing skeleton in the vertical direction of the BNNS / MXene functional filler, and then pouring liquid silicone rubber; The BNNS / MXene functional filler is prepared by combining boron nitride nanosheets and MXene through the electrostatic adsorption force of positive and negative charges; The preparation method comprises the following steps: (1) Prepare MXene with negative surface charge and BNNS with positive surface charge respectively; (2) The BNNS with positive charge on the surface and the MXene with negative charge on the surface are prepared into a suspension in a mass ratio of 20:0.75, and then placed on a stirring platform and stirred at 100-300 rpm for 10-60 min, and then allowed to stand for 24 h. The two materials with different positive and negative charges will be combined together by electrostatic adsorption during the standing process. After the precipitate is obtained, it is repeatedly washed with water, centrifuged and dried to obtain the BNNS / MXene functional filler; (3) The BNNS / MXene functional filler and xanthan gum are configured into a water suspension, and the configured suspension is placed on a directional freezing platform with the cold source at the bottom. Ice crystals will grow vertically from the bottom to the top, thereby squeezing the filler into a vertical heat-conducting and wave-absorbing skeleton ice structure during the growth of ice crystals from bottom to top through the ice template method. This ice structure is then cold-dried in a freeze dryer to remove the ice crystals, thereby obtaining a vertical heat-conducting and wave-absorbing skeleton; (4) pouring liquid silicone rubber into the prepared heat-conducting and wave-absorbing skeleton to fill the gaps left by the evaporated ice crystals, and then curing to obtain a MXene-enhanced heat-conducting and wave-absorbing composite material; Preparation of MXene with negative surface charge: Ti 3 AlC 2 The MAX phase is placed in a hydrochloric acid solution of LiF and the Al atomic layer is etched away; Preparation of BNNS with positive charge on the surface: Hexagonal boron nitride with a diameter of 10 to 30 μm is placed in a ball mill according to a ball-to-material mass ratio of (10 to 40): 1, the ball milling speed is 300 to 500 r / min, the ball milling time is 24 to 48 hours, and the ball mill is centrifuged and placed in an oven for drying to obtain BNNS; BNNS is placed in a hexadecyltrimethylammonium bromide solution with a concentration of 1 to 10 g / L and ultrasonically treated for 2 to 4 hours, and then dried to obtain BNNS with positive charge on the surface; The concentration of xanthan gum in the suspension of step (3) is 0.02-5 g / L, and the concentration of BNNS / MXene functional filler is 10-50 g / L.

2. The method for preparing the MXene-enhanced thermally conductive and wave-absorbing composite material according to claim 1, Features: In step (4), the prepared heat-conducting and wave-absorbing skeleton is immersed in the prepared silicone rubber solution, heated to 80° C., and cured for 20 minutes.

3. The method for preparing the MXene-enhanced thermally conductive and wave-absorbing composite material according to claim 1, Features: The preparation of MXene with negative charge on the surface includes the following steps: 40 mL of 9 mol / L concentrated hydrochloric acid is prepared in a 100 mL polytetrafluoroethylene container, and then 2 g of lithium fluoride is weighed and slowly added to the above solution, and stirring is started for 30 min; 2 g of Ti 3 AlC 2 The MAX phase was slowly added to the solution, and then the reaction mixture was placed in a 40°C water bath and stirred continuously for 36 hours. After the reaction was completed, it was repeatedly washed with water until the solution was neutral, and then the reaction mixture was placed in an ultrasonic treatment for 30 minutes. The reactants were then loaded into centrifuge tubes in batches, centrifuged at 3500 rpm for 20 minutes, and the supernatant was taken. The above steps were repeated until the supernatant was clear, and the supernatant was concentrated by centrifugation at 11000 rpm for 40 minutes, and the sample bottle was filled with argon inert gas protection, and the concentration of the MXene solution was tested by sampling.

4. The method for preparing the MXene-enhanced thermally conductive and wave-absorbing composite material according to claim 1, Features: The mass ratio of the terminal vinyl silicone oil, hydrogen-containing silicone oil, inhibitor and accelerator in the liquid silicone rubber is 100: (10-20): (2-10): (1-10). The preparation method of the liquid silicone rubber comprises the following steps: the terminal vinyl silicone oil, hydrogen-containing silicone oil and platinum inhibitor of the addition type silicone rubber are weighed in mass ratio and then subjected to vacuum degassing and mixing at a rotation speed of 800 rpm; after uniform mixing, the platinum catalyst is weighed in mass ratio and then subjected to vacuum degassing and mixing at a rotation speed of 1500 rpm.

5. A MXene-reinforced thermally conductive and wave-absorbing composite material prepared according to the method according to any one of claims 1 to 4.

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