Integrated ordered structure materials, methods of making and applications thereof

Abstract

The application discloses an integrated ordered structure material and a preparation method and application thereof. The prepared integrated ordered structure material comprises a high-enthalpy bottom layer and a low-infrared-emissivity top layer arranged in sequence. The high-enthalpy bottom layer is a heat-stable gel layer solidified by a high-capacity phase change material. The low-infrared-emissivity top layer is an infrared-transparent resin layer filled with metal fillers. The integrated ordered structure material can cope with reliable infrared stealth in a wide temperature range, and can exhibit excellent compatible stealth protection capability for static and dynamic heat sources, and reliable infrared "false display" capability. The integrated ordered structure material successfully breaks the dependence of traditional materials on a narrow application temperature range, and has a wide application prospect in the field of long-term infrared thermal stealth.

Description

Technical Field

[0001] The present invention relates to the technical field of stealth materials, in particular to the technical field of infrared stealth materials. Background Art

[0002] Unlike visible light and radar detection, which use reflected signals to obtain information, infrared radiation is passive and therefore needs to be hidden. According to the Stefan-Boltzmann law, the total amount of radiation emitted by an object is proportional to its emissivity and the fourth power of its absolute temperature. Therefore, the key to reducing radiation intensity and improving infrared stealth capability lies in reducing infrared emissivity and controlling the target surface temperature in order to improve the target's stealth effect.

[0003] Emissivity engineering is considered a promising approach, including but not limited to photonic crystals, doped semiconductors, and infrared coatings. Among them, the unique filtering properties of photonic crystals can effectively reduce the emissivity of atmospheric windows, as shown by Zhang et al. (J.-K. Zhang, J.-M. Shi, D.-P. Zhao, Y.-Z. Chen, Optical Engineering. 2017,56.) A one-dimensional heterostructure photonic crystal was obtained by vacuum evaporation sputtering of Te and ZnSe, and the emissivity of the one-dimensional heterostructure photonic crystal in the 3-5-μm and 8-14 μm bands was 0.072 and 0.194, respectively; the tunability and compatibility of semiconductor doped infrared stealth technology are attractive in multi-band stealth, such as Xu et al. (C. Xu, B. Wang, M.Yan, Y. Pang, Y. Meng, W. Wang, J. Wang, Q. Fan, S. Qu, Infrared Physics & Technology. Journal of Materials Science: Materials in Electronics. 2020, 105.) designed a metasurface with an ITO / dielectric / ITO sandwich structure and achieved a low infrared emissivity of 0.52 by adjusting the filling ratio of ITO. Infrared coatings, due to their high infrared reflectivity, can hide objects from infrared detection and have become a new area of ​​interest. For example, Huang et al. (X. Huang, W. Rao, Y.Chen, W. Ding, H. Zhu, M. Yu, J. Chen, Q. Zhang, Carbon. ACS Applied Materials & Interfaces.2016, 27, 5543-5548.) Inexpensive and readily available homogeneous aluminum was incorporated into different resin substrates as a metal filler. The effects of different simple coating methods, such as spraying, brushing, blade coating, and flow coating, on the radiation characteristics of the coating were compared. Ultimately, an infrared coating with an emissivity of 0.31 was obtained by spraying. From the perspective of scalability, the infrared coating preparation method is simple and can be quickly implemented without changing the target shape and structure. It is not restricted by the target geometry and structure, which is conducive to large-scale and comprehensive application.

[0004] In order to meet the long-term camouflage requirements in a wide temperature range, we need to improve the versatility of stealth methods. Combining thermal management technology with emissivity engineering is a potential and reliable way to solve this problem. Chemical Engineering Journal. 2023, 213.) Chitosan-derived carbon aerogel is used as a skeleton and loaded with vanadium dioxide (VO2), a transition metal phase change material with thermotropic emissivity. The emissivity of the resulting composite structure gradually decreases with increasing temperature, reaching 0.581 at 100°C. The average temperature of the composite structure after standing for 180 seconds in a 120°C environment is 32.8°C, demonstrating excellent thermal stealth performance. However, such biomass-derived carbon aerogels are often very strong. Although this allows them to withstand loads exceeding 3,000 to 5,000 times their own weight, it also causes them to lose elasticity and flexibility (making them unable to conform to arbitrary targets).

[0005] Hydrogels have attracted widespread attention in many fields as ideal flexible substrates due to their flexibility, stretchability and biocompatibility; Zhu et al. (T.-y. Zhu, W.-j. Jiang, S. Wu, Z.-j. Huang, Y.-l. Liu, X.-d. Qi, Y. Wang, Figure 1 2024, 16, 15372-15382.) Polyacrylamide was used to encapsulate sodium sulfate decahydrate and conductive filler MXene / PEDOT:PSS, and the surface temperature of the obtained flexible phase-change organic hydrogel was 42.1°C after covering a 65°C hot target for 6 minutes; In addition, Zhou et al. (Y.-C.Zhou, J. Yang, L. Bai, R.-Y. Bao, M.-B. Yang, W. Yang, Figure 2 Figure 32022, 446.) By integrating polyvinyl alcohol hydrogel substrate with paraffin phase change microspheres, a flexible phase change hydrogel with excellent mechanical and thermophysical properties was prepared (it can provide nearly 30 min of stealth protection for a 50℃ heat source); although the phase change hydrogel exhibits excellent flexibility and stretchability, a large amount of water contained therein can evaporate and dissipate in the high temperature range, thereby resulting in that the infrared stealth based on the hydrogel is mostly limited to the low temperature field (i.e. below 70℃); in addition, since there is a threshold for the phase change heat absorption of the phase change material, it can only achieve short-term infrared stealth; at present, long-term infrared camouflage of important targets in extreme environments is still a great challenge and needs to be solved. SUMMARY

[0006] The purpose of the present application is to solve the problems in the prior art, and to propose an integrated ordered structure material and its preparation method and application. The prepared integrated ordered structure material not only can cope with reliable infrared stealth in a wide temperature range, but also can exhibit excellent compatibility stealth protection ability for static and dynamic heat sources, and show reliable infrared "false" ability, successfully breaking the dependence of traditional materials on narrow application temperature range, and having wide application prospect in the field of long-term infrared thermal stealth.

[0007] To achieve the above-mentioned purpose, the present application realizes the following technical scheme:

[0008] The integrated ordered structure material comprises a high-enthalpy bottom layer and a low-infrared-emissivity top layer arranged in sequence, the high-enthalpy bottom layer is a heat-stable gel layer loaded with high-capacity phase change material, and the low-infrared-emissivity top layer is an infrared-transparent resin layer filled with metal fillers; wherein the high-enthalpy bottom layer can absorb heat in the heat conduction process by using phase change enthalpy to increase the axial heat transfer resistance, and the low-infrared-emissivity top layer can realize "thermal camouflage" of apparent temperature by using multi-stage reflection of thermal radiation of metal fillers.

[0009] As a preferred, a high-thermal-resistance middle layer is further arranged between the high-enthalpy bottom layer and the low-infrared-emissivity top layer, and the high-thermal-resistance middle layer is a polydimethylsiloxane resin layer. Wherein, on the one hand, the high-thermal-resistance middle layer can effectively weaken the heat transfer in the structure, reduce the infrared radiation intensity of the local high temperature area, make the surface temperature distribution of the structure more uniform to reduce the detectability of the target under the infrared detection equipment, on the other hand, it can also reduce the influence of temperature gradient on the thermal stress of infrared coating, thereby slowing down the aging and corrosion speed of the coating, prolonging the service life of the stealth system; such three-layer design can make the stealth system have heat absorption, heat insulation and low radiation performance at the same time, thereby combining heat management technology and emissivity engineering organically.

[0010] Further, the high thermal resistance middle layer is coated on all or part of the surface of the high enthalpy bottom layer except the bottom surface, and the low infrared emissivity top layer is coated on the top surface of the high thermal resistance middle layer; wherein the high thermal resistance middle layer can enhance the adhesion between the high enthalpy bottom layer and the low infrared emissivity top layer to avoid the double-layer from being detached by stress friction; this is because the infrared transparent resin layer can form a firm chemical bond with the polydimethylsiloxane resin layer by using polar groups, so that the low infrared emissivity top layer exhibits excellent 1st level adhesive strength.

[0011] Further, the thickness of the high thermal resistance middle layer is controlled to be 3.0-5.0 mm, and the thickness of the low infrared emissivity top layer is controlled to be 220-280 um.

[0012] Further, the high enthalpy bottom layer exhibits a progressive close-packed worm-like rod structure, and the low infrared emissivity top layer is in a layer-by-layer stacked form of metal fillers in the infrared transparent resin layer; wherein the low infrared emissivity top layer can reflect thermal radiation by the layer-by-layer stacked metal fillers in multiple stages, thereby reducing the absorption and emission rates (Kirchhoff's law) of the stealth coating to thermal radiation and regulating the radiation temperature.

[0013] A preparation method of an integrated ordered structure material, comprising the following steps:

[0014] a) Preparation of the high enthalpy bottom layer: polyvinyl alcohol, fatty acid, acidic reagent and aldehyde crosslinking agent are sequentially mixed and reacted, and then the mixed solution is solidified and formed, and sequentially subjected to washing and drying treatment to obtain a fatty acid-based phase change gel layer as the high enthalpy bottom layer;

[0015] b) Preparation of the high thermal resistance middle layer: dimethylsiloxane monomer and crosslinking agent are uniformly mixed and poured into a mold containing the high enthalpy bottom layer, and then the mixed solution is solidified outside the high enthalpy bottom layer to form the high thermal resistance middle layer;

[0016] c) Preparation of the low infrared emissivity top layer: metal fillers are uniformly dispersed in an infrared transparent resin base material, and then the dispersion liquid is sprayed outside the high thermal resistance middle layer and solidified to form the low infrared emissivity top layer.

[0017] As preferred, in the step a), the loading amount of the fatty acid is 60-80 wt%, the mass-volume ratio of the fatty acid to the acidic agent is 0.001-0.003 g / ul, the volume ratio of the acidic agent to the aldehyde cross-linking agent is 6-10:1, the fatty acid is one or a combination of several of caproic acid, lauric acid, myristic acid, palmitic acid and stearic acid, the acidic agent is hydrochloric acid, and the aldehyde cross-linking agent is one or a combination of several of formaldehyde, acetaldehyde, n-butyraldehyde, glutaraldehyde and crotonaldehyde; wherein the fatty acid is a kind of alkanoic acid with general carboxylic acid chemical properties, and the aldehyde cross-linking agent is an aldehyde substance capable of condensation reaction with polyvinyl alcohol under acidic conditions; in addition, stearic acid is a preferred choice due to its relatively high melting point (76℃) and heat enthalpy (208.3 kJ / kg), better heat absorption and storage capacity, and natural and wide source (extracted from vegetable oil and animal fat); glutaraldehyde is a preferred choice due to its dialdehyde structure, which can more effectively chemically cross-link with polyvinyl alcohol through condensation reaction and form stable covalent bonds, thereby significantly improving the cross-linking degree and mechanical properties, heat resistance, chemical resistance, and biological and tissue compatibility of the material.

[0018] Further, in the step a), the polyvinyl alcohol is first dissolved in deionized water, and then the fatty acid and hydrochloric acid are added in sequence, followed by the addition of the aldehyde cross-linking agent after stirring for a period of time, and then the mixture is quickly transferred to a mold, and after the phase change gel is formed (the phase change gel can be quickly formed within 5 min), the phase change gel layer is demolded and washed with deionized water and vacuum dried in an oven to obtain the fatty acid-based phase change gel layer.

[0019] Further, in the step a), the polyvinyl alcohol is first dissolved at a temperature of 60-100℃, and then the fatty acid, hydrochloric acid and aldehyde cross-linking agent are sequentially dissolved after the solution temperature drops to room temperature, the vacuum drying temperature is 45-65℃, and the vacuum drying time is 15-25h.

[0020] As preferred, in the step b), the cross-linking agent is one or a combination of several of methyltrichlorosilane, propylsilane and phenyltrichlorosilane, and the mass ratio of the dimethylsiloxane monomer to the cross-linking agent is 8-12:1.

[0021] Further, in the step b), the mixed solution is subjected to defoaming treatment before being cured on the high-enthalpy bottom layer.

[0022] Further, in the step b), the defoaming is performed at room temperature for 20-40 min, the curing temperature is 45-65℃, and the curing time is 4-8h.

[0023] As preferred, in the step c), the loading amount of the metal filler is 30-70wt%, the metal filler is one or a combination of several of aluminum powder, iron powder, zinc powder, silver powder and gold powder, the shape of the metal filler is one or a combination of several of spherical, rod-like, scale-like and irregular, the maximum distance between two points on the surface where the metal filler is located is controlled to be 20-25um, and the infrared transparent resin is one or a combination of several of fluorocarbon resin, epoxy resin, polyurethane resin and acrylic resin; wherein the infrared transparent resin is an infrared transparent substance without strong absorption in the far infrared wave band; in addition, the fluorocarbon resin has excellent heat resistance and chemical resistance due to the firm C-F bond as the skeleton, and can remain stable under high temperature and various chemical environments, and is particularly suitable for fields requiring long-term durability; the metal filler has a low absorption rate due to the close arrangement of atoms into a close-packed structure, thereby showing a low emissivity in the infrared wave band; in terms of shape, scale-like powder is preferentially selected due to the large diameter-thickness ratio and good spreading property, and is easy to float to the surface of the coating.

[0024] Further, in the step c), the dispersion liquid is first adjusted in viscosity by a viscosity adjusting agent before being sprayed and is first dried after being sprayed.

[0025] Further, in the step c), the viscosity adjusting agent is butyl acetate, and the dispersion liquid is adjusted to have good flowability and no obvious particles formed by filler agglomeration, is left to stand for defoaming for 10-14h at room temperature, and is cured at a temperature of 45-65℃ for 4-8h.

[0026] The integrated ordered structure material is applied to infrared stealth; taking a three-layer structure as an example, on the one hand, a heat-stable gel layer (i.e. high-enthalpy bottom layer) loaded with a high-enthalpy phase change material with high-enthalpy characteristics will serve as a super-absorbing layer of heat and will form a heat barrier together with a polydimethylsiloxane resin layer (i.e. high-thermal-resistance middle layer) with high-thermal-resistance characteristics to realize dynamic coordinated temperature control, and on the other hand, a low-infrared-emissivity top layer can exhibit low infrared emissivity by using multi-stage reflection of infrared waves by metal fillers; such a design combining heat management technology and emissivity engineering can easily realize long-term infrared detection concealment effect; the integrated ordered structure material has the functions of heat absorption, heat insulation and thermal radiation attenuation, and can realize reliable and persistent infrared stealth for both static and dynamic high-temperature heat sources.

[0027] The beneficial effects of the present application are as follows:

[0028] 1) By adopting high-enthalpy bottom layer and low-infrared emissivity top layer as the base layer, on the one hand, the high-enthalpy bottom layer can fully absorb the heat in the heat conduction process by using the phase change enthalpy to increase the axial heat transfer resistance, on the other hand, the low-infrared emissivity top layer can also use the multi-stage reflection of thermal radiation by metal fillers to achieve the "thermal camouflage" of apparent temperature;

[0029] 2) By adding a high-thermal-resistance middle layer between the high-enthalpy bottom layer and the low-infrared emissivity top layer to form a sandwich-like composite system, not only the high-efficiency heat absorption, heat insulation and low-radiation performance are integrated, but also the excellent high-temperature flexibility makes the series structure effectively adhere to any surface and implement high-efficiency infrared camouflage for 10h, finally ensuring that the obtained integrated ordered structure material exhibits excellent compatibility and invisibility protection ability to static and dynamic heat sources, and has more versatility and universality, breaking the dependence of traditional hydrogel-based infrared stealth materials on narrow application temperature range, and having a wide application prospect in the field of infrared thermal stealth;

[0030] 3) By wrapping the high-thermal-resistance middle layer around all or part of the surface of the high-enthalpy bottom layer except the bottom surface, and then directly loading the low-infrared emissivity top layer on the high-thermal-resistance middle layer by spraying and curing, the adhesion between the high-enthalpy bottom layer and the low-infrared emissivity top layer is enhanced, and the double-layer stress friction detachment is avoided (the polar groups in the low-infrared emissivity top layer can form a firm chemical bond with the high-thermal-resistance middle layer made of polydimethylsiloxane resin, so that the low-infrared emissivity top layer shows excellent 1st level adhesive strength);

[0031] 4) The integrated ordered structure material disclosed in the present application can be applied in single layer (only low infrared emissivity top layer), double layer combination (high enthalpy bottom layer and low infrared emissivity top layer) and three layer combination (high enthalpy bottom layer, high thermal resistance middle layer and low infrared emissivity top layer) to adapt to different thermal targets in different states and temperatures (for low temperature thermal target such as human body, only the low infrared emissivity top layer in single layer can exhibit excellent thermal camouflage ability; for static medium temperature heat source such as 80℃, the composite structure composed of high enthalpy bottom layer and low infrared emissivity top layer can effectively protect the medium temperature heat source from the aspects of heat conduction and heat radiation; for dynamic medium temperature heat source with fluctuation in temperature in the range of 45-80℃, the composite structure composed of high enthalpy bottom layer and low infrared emissivity top layer can successfully inhibit temperature fluctuation by using temperature hysteresis generated by phase change behavior; for static high temperature heat source such as 100℃, the composite structure composed of high enthalpy bottom layer, high thermal resistance middle layer and low infrared emissivity top layer can effectively weaken the heat transfer in the axial direction of the structure by using low thermal conductivity and thickness-adjustable polydimethylsiloxane resin, solving the camouflage "weakness" of single / two combined components in high temperature stealth; for dynamic high temperature heat source with fluctuation in temperature in the range of 45-100℃, the composite structure composed of high enthalpy bottom layer, high thermal resistance middle layer and low infrared emissivity top layer can effectively weaken the temperature rise by using high phase change enthalpy through melting behavior in the heating process and solidification behavior in the cooling process, thereby greatly reducing the exposure risk of dynamic thermal target with high frequency temperature change).

[0032] The features and advantages of the present application will be described in detail with examples in conjunction with the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 4 is a preparation flow chart of the high enthalpy bottom layer of example one;

[0034] Figure 5 is a preparation flow chart of the low infrared emissivity top layer of example one;

[0035] Figure 6 is a structure schematic diagram of the integrated ordered structure material of example one;

[0036] Figure 7 is an infrared stealth mechanism diagram of the integrated ordered structure material of example one;

[0037] Figure 8 is an SEM diagram of the low infrared emissivity top layer prepared in example one and example two;

[0038] Figure 9 is an infrared emissivity, mirror gloss and adhesion strength diagram of the low infrared emissivity top layer prepared in example one and example two;

[0039] Figure 10 FTIR spectra of PVA hydrogel, SA, PVA, and the fatty acid-based phase change gel layer prepared in Example 1;

[0040] Figure 11 The mechanical properties and physical images of the fatty acid-based phase change gel layers prepared in Example 1 and Example 3 at room temperature and 80°C;

[0041] Figure 12 1 is an SEM image of the fatty acid-based phase change gel layer prepared in Example 1 and Example 3;

[0042] Figure 13 1 is a DSC graph of pure stearic acid and the fatty acid-based phase change gel layers prepared in Example 1 and Example 3;

[0043] Figure 14 1 is a time-temperature curve of the integrated ordered structure material prepared in Example 1 and Example 4 on a heating platform at 100° C.;

[0044] Figure 15 This is an infrared thermal imaging image of the low infrared emissivity top layer prepared in Example 1 on the human body surface;

[0045] Figure 16 This is an infrared thermal image of the fatty acid-based phase change gel / infrared coating composite structure prepared in Example 1 on a static 80°C heating table;

[0046] Figure 17 This is an infrared thermal image of the fatty acid-based phase change gel / infrared coating composite structure prepared in Example 1 placed on a dynamic heat source (45-80°C);

[0047] Figure 1 This is a diagram of the stealth mechanism of the composite structure composed of BPCG-75 and FC / Al-5 / 5 in Test Example 7;

[0048] Figure 2 This is an infrared thermal image of the integrated ordered structure material prepared in Example 1 on a static 100°C heating stage;

[0049] Figure 3 This is an infrared thermal imaging image of the integrated ordered structure material prepared in Example 1 on a dynamic heat source (45-100°C). DETAILED DESCRIPTION

[0050] Example 1:

[0051] The integrated ordered structure material was prepared according to the following steps:

[0052] a) Preparation of high enthalpy bottom layer:

[0053] SeeFigure 4 Firstly, 0.5 g of polyvinyl alcohol powder (PVA powder) was weighed and dissolved in 9.5 ml of deionized water under the condition of heating and stirring at 80°C (stirring for 1.5 h to promote the full dissolution and dispersion of polyvinyl alcohol); after the temperature of the polyvinyl alcohol solution (PVA solution) was reduced to room temperature, 1.5 g of stearic acid and 800 ul of hydrochloric acid were sequentially added to the polyvinyl alcohol solution and stirred for 1 h to allow the polyvinyl alcohol to fully esterify with stearic acid under acidic conditions; then, 100 ul of glutaraldehyde solution was added to the polyvinyl alcohol / stearic acid mixed solution (PVA / SA solution), and the polyvinyl alcohol / stearic acid / glutaraldehyde hydrogel (PVA / SA / GA hydrogel) could be quickly formed within 5 min; next, the hydrogel was washed with deionized water until the pH of the washing liquid was 7, and then it was placed in an oven at 55°C for drying for 20 h to promote the complete evaporation of its moisture, thereby obtaining the final fatty acid-based phase change gel (PVA / SA / GA phase change gel), marked as BPCG-75; wherein 75 represents the mass fraction of stearic acid in the composite phase change material;

[0054] b) Preparation of high thermal resistance middle layer:

[0055] A certain mass of dimethylsiloxane monomer and crosslinking agent were weighed according to a mass ratio of 10:1 and poured into a mold containing BPCG-75 after being uniformly stirred; next, after standing at room temperature for 30 min to eliminate bubbles, the combined component was transferred to a vacuum drying oven at 55°C, and a high thermal resistance middle layer was obtained after high-temperature curing for 6 hours, and was marked as P4; wherein 4 represents the thickness of the polydimethylsiloxane resin layer and the unit is mm;

[0056] c) Preparation of low infrared emissivity top layer:

[0057] Referring to Figure 5, 0.03 g of fluorocarbon resin-A and 0.2 g of fluorocarbon resin-B were weighed into a glass container, stirred and mixed thoroughly to obtain a resin matrix for coating; then, 0.115 g of flaky Al powder was weighed and dispersed into the resin matrix, and an appropriate amount of butyl acetate was added to adjust the viscosity of the coating to a suitable range (until it has good fluidity and no obvious particulate matter is observed in the solution due to filler agglomeration; the part of the liquid except the Al powder is FEVE / Butylacetate solution; then, using a lithium electric air pump spray pen, the obtained coating was uniformly sprayed onto the P4 surface at 15 PSI (by controlling the spraying distance and time, the coating thickness was limited to 250 um); after drying at room temperature for 12 h until the solvent butyl acetate was completely volatilized, the coating was placed in an oven at 55°C for 5 h, and finally a low-emissivity infrared coating (FC / Al coating) was obtained and recorded as FC / Al-5 / 5; where 5 / 5 represents the mass ratio of fluorocarbon resin (0.23 x 50%, and 50% is the solid content (solid content refers to the ratio of the final mass to the initial mass after heating at 100°C under vacuum for 30 min)) to Al powder.

[0058] Finally, the structure and infrared stealth mechanism of the obtained integrated ordered structure material based on biomass phase change gel are as shown in Figure 6 and Figure 6 (FC / Al represents the low infrared emissivity top layer, PDMS represents the high thermal resistance middle layer, and BPCG represents the high enthalpy bottom layer, and the same below); the integrated ordered structure material has the following advantages:

[0059] 1) On the one hand, stearic acid as the main phase change material is widely present in nature (can be directly extracted from animal fat and vegetable fat) and is environmentally friendly, and on the other hand, fluorocarbon resin as the top thermal radiation component has the characteristics of infrared transparency and chemical stability, which can effectively encapsulate cheap and easily available flaky aluminum powder, thereby forming extremely low far infrared emissivity;

[0060] 2) The preparation method is low in cost and simple in process, mainly through crosslinking preparation and thermal curing connection;

[0061] 3) The structure is simple and is a stable cylindrical whole composed of three parts (it should be emphasized that the shape of the integrated ordered structure material is determined by the shape of the mold, and the mold can be cylindrical, prismatic, circular truncated cone or other special shapes, and those skilled in the art should make adaptive modifications to the shape of the stealth system under the guidance of the embodiments of the present application, and the embodiments will not be illustrated again);

[0062] 4) It has thermal-induced flexibility and can exhibit excellent compatibility stealth protection capability to static and dynamic uneven heat source surfaces.

[0063] Example Two:

[0064] The loading of Al powder was changed from 50wt% to 30wt%, 40wt%, 60wt% and 70wt%; other conditions were the same as Example One.

[0065] Example Three:

[0066] The loading of stearic acid was changed from 75wt% to 60wt%, 65wt%, 70wt% and 80wt%; other conditions were the same as Example One.

[0067] Example Four:

[0068] The thickness of the polydimethylsiloxane resin layer was changed from 4.0mm to 3.0mm, 3.5mm, 4.5mm and 5.0mm; other conditions were the same as Example One.

[0069] Test Example One:

[0070] For Example One and Example Two, the morphological characteristics and optical properties of the infrared coating (i.e. the low infrared emissivity top layer) are listed in Figure 5 and Figure 6 respectively; wherein FC / Al-5 / 5 is the pattern of Example One with the loading of Al powder controlled at 50wt%, while FC / Al-7 / 3, FC / Al-6 / 4, FC / Al-4 / 6 and FC / Al-3 / 7 are the patterns of Example Two with the loading of Al powder controlled at 30wt%, 40wt%, 60wt% and 70wt% respectively, and the same below; in addition, in Figure 6 , the incident angle of mirror gloss is 60°.

[0071] As shown in Figure 6 , when the content of aluminum powder is low (such as FC / Al-7 / 3), the functional filler cannot completely cover the entire surface of the coating; the strong infrared light absorption caused by a large number of pores and the deformed orientation of aluminum powder caused by stress shrinkage will increase the emissivity of the coating (see part (a) of Figure 5 ); when the content of aluminum powder is too high (such as FC / Al-4 / 6 and FC / Al-3 / 7), due to the brightness of the metal, this structure produces strong reflection of visible light, thereby increasing the exposure risk of the coating in the visual (see part (b) of Figure 1 ); and for FC / Al-5 / 5, the compact surface formed by the appropriate filler concentration ensures the ordered parallel arrangement of the flaky aluminum powder, and the emissivity can be optimized from 0.255 when the content of aluminum powder is 30wt% to 0.221, so that the coating has excellent ultra-low infrared emissivity, and enhances its ability to reflect far-infrared radiation in the wavelength range of 8~14μm; in addition, good mechanical properties are also a basic requirement for the expansion of the application of the infrared coating; see Figure 7In part (c), since the polar groups in the fluorocarbon resin can form a strong chemical bond with the substrate, when the aluminum powder content is lower than 50wt%, the FC / Al-x coating exhibits excellent level 1 bonding strength and can firmly adhere to the substrate surface, achieving effective thermal camouflage protection for thermal targets.

[0072] After comprehensively considering the infrared emissivity, glossiness and mechanical properties of the infrared coating, it was finally determined that the optimal total filler content in the coating was 50wt% and the average film thickness was 258um (see Figure 7 (f) of the .

[0073] Test Example 2:

[0074] In order to improve the versatility of camouflage technology, the present invention further incorporates thermal management technology on the basis of stealth coating, thereby expanding the temperature range of "thermal stealth"; wherein, the composite phase change gel (i.e., fatty acid-based phase change gel layer) is prepared by two-step cross-linking of polyvinyl alcohol and stearic acid; Figure 8 As shown, in order to improve the encapsulation rate of the phase change material, in the first cross-linking step, the present invention utilizes the esterification reaction between polyvinyl alcohol and stearic acid under acidic conditions to promote the linking of part of the stearic acid to the long chain of polyvinyl alcohol to form chained stearic acid; to further encapsulate the remaining free stearic acid and improve the high-temperature anti-leakage properties of BPCG, glutaraldehyde is introduced into the polyvinyl alcohol / stearic acid mixed solution and rapidly undergoes a condensation reaction with polyvinyl alcohol under acidic conditions (the large number of acetal bonds generated ensure the formation of a secondary cross-linked network, further strengthening the internal structure of BPCG and enhancing its reliability in practical applications); then, after simple solvent replacement and drying treatment, BPCG with high enthalpy characteristics is synthesized.

[0075] For Example 1, this test example uses FTIR spectroscopy to characterize the molecular structure and chemical bonds of the fatty acid-based phase change gel layer, and the results are as follows: Figure 8 shown.

[0076] Overall, BPCG-75 retains all characteristic peaks of polyvinyl alcohol and stearic acid. Specifically, compared with polyvinyl alcohol, BPCG-75 has a −1 The stretching vibration peak of OH at 1025 cm-1 is weakened, and the peak at 1025 cm-1 appears. −1 The COC stretching vibration absorption peak at , which indicates that the carboxylic acid in the stearic acid component reacts with the hydroxyl group in the polyvinyl alcohol to form an esterification reaction; In addition, Figure 8 In this experiment, PVA represents polyvinyl alcohol and SA represents stearic acid. To further illustrate the cross-linking effect of glutaraldehyde, a polyvinyl alcohol hydrogel without stearic acid (i.e., PVA hydrogel) was also prepared. −1The significant decrease in the peak at 1118 cm −1 The peak at 3437 cm is slightly blue-shifted and −1 The slight red shift of the peak at supports the hypothesis that the cross-linking of the alcohol group of polyvinyl alcohol and the CHO group of glutaraldehyde leads to the formation of ether (CO-) and acetal ring (COC); thus, the use of FTIR provides strong evidence for the two-step cross-linking of the fatty acid-based phase change gel layer.

[0077] Test Example 3:

[0078] For Example 1 and Example 3, this test example used a universal material testing machine to conduct tensile tests on each sample, and the results are as follows: Figure 8 shown; among them, Figure 8 Part (a) shows the elastic modulus, tensile strength and elongation at break of each sample of Example 1 and Example 3 at room temperature, while Figure 9 Part (b) shows the stress-strain curve of BPCG-75 at 80°C; BPCG-60, BPCG-65, BPCG-70, and BPCG-80 represent stearic acid loadings of 60 wt%, 65 wt%, 70 wt%, and 80 wt%, respectively, the same below.

[0079] See Figure 10 As shown in Table 1, due to the evaporation of the solvent water in the phase change gel, the polyvinyl alcohol layer directly encapsulates stearic acid through a two-step cross-linking reaction. The polyvinyl alcohol as the continuous phase is interrupted by the discretely distributed stearic acid, and stress concentration points appear during the stretching process. Therefore, all samples show brittle fracture characteristics at room temperature, and the overall elongation at break is below 6%; Interestingly, with the increase of stearic acid content, the elastic modulus and tensile strength of the fatty acid-based phase change gel layer decrease as a whole, and the elongation at break shows a "volcano" type change, and reaches a peak at BPCG-75; the reason for this phenomenon may be related to Compared with stearic acid, the hardness of dry polyvinyl alcohol gel is higher; in addition, compared with other styles, the three-dimensional continuous fibrous grid of BPCG-75 is denser (the compact network structure is conducive to dispersing the concentrated stress during the stretching process, thereby causing a decrease in tensile strength and an increase in elongation at break); when the temperature is further increased to above the melting point of stearic acid, the stearic acid in a liquid flow state causes the tensile stress to be widely distributed, effectively reducing the tendency to brittle fracture, and showing amazing flexibility and stretchability; for Example 1, its elastic modulus, tensile strength and elongation at break are 3.70 MPa, 0.59 MPa and 85.78% respectively, and it can be easily bent under the pressure of an adult's palm (such as Figure 10 (as shown in part (c) of the ).

[0080] Therefore, from the perspective of mechanical properties, BPCG-75 not only shows relatively better adaptability at room temperature, but also has excellent flexibility in high temperature environment, and is more easily to meet the needs of complex application environment; in addition, Figure 10 The surface morphology characteristics of BPCG-60, BPCG-65, BPCG-70, BPCG-75 and BPCG-80 are shown; when the relative content of stearic acid is increased from 60wt% to 75wt%, with the gradual deepening of the two-step crosslinking degree, it respectively shows the progressive dense packing of the worm-like rod structure in the SEM pattern; however, when the content of stearic acid is too high, such as BPCG-80 (the loading amount of stearic acid is 80wt%), too much stearic acid will be wrapped on the surface of the rod structure, thereby forming the "rock" like appearance of block layer interlacing; therefore, the moderate amount of phase change material encapsulation is crucial for the formation of three-dimensional continuous fiber-like grid in the composite structure (with 75wt% of stearic acid addition as the best).

[0081] Table 1 Mechanical properties of each pattern of Example One and Example Three

[0082]

[0083] Test Example Four:

[0084] For Example One and Example Three, the heat flow curves of the phase change process of each pattern are tested by using a differential scanning calorimeter, and the results are listed in Figure 10 ; wherein, Figure 11 Part (a) of is the DSC curve of stearic acid, Figure 11 Part (b) of is the results of each pattern in the heating stage, and part (c) is the results of each pattern in the cooling stage.

[0085] Compared with the spontaneous phase change of stearic acid (see Figure 12 Part (a)), the phase change peaks of each pattern show a stage-like heat absorption and release; this two-stage phase change behavior may be caused by the different properties of the chain stearic acid and the free stearic acid in each pattern; wherein, compared with the chain stearic acid, the chemical environment of the free stearic acid is more free and is not restricted by the associated ester bond, so that it yields to heat first in the temperature rising stage; with the further increase of temperature, the stronger phase change heat driving force improves the lattice change and the movement tendency of the molecular chain of the chain stearic acid, thereby prompting each pattern to show a double-peak endothermic behavior; for the same reason, in the temperature decreasing stage, the phase change of the free stearic acid and the chain stearic acid in turn contributes to the first and second exothermic peaks on the DSC curve.

[0086] Overall, due to the polymer base polyvinyl alcohol and the amount of crosslinking agent is always far less than the main phase change material stearic acid, the above each formula of the phase change parameters and pure stearic acid, there is no big change (see Table 2).

[0087] Table 2 DSC curve data of each formula of Example 1 and Example 3

[0088]

[0089] In addition, in Table 2, the unit of temperature is ℃, and the unit of enthalpy is J / g.

[0090] Test Example Five:

[0091] For Example 1 and Example 4, this test example uses a data collector to record the surface temperature of the stealth system, and the results are listed in Figure 13 .

[0092] As Figure 14 shown, the contribution of the polydimethylsiloxane resin layer thickened by 0.5mm to thermal insulation is weakened in turn, and the surface middle temperature of the series structure is balanced at 70℃, 63℃, 59℃, 56℃ and 54℃ in turn; therefore, the weakening degree of temperature for each 0.5mm thickened polydimethylsiloxane resin layer is nonlinear; blindly thickening the polydimethylsiloxane resin layer can effectively reduce the average surface temperature of the stealth system, but this is at the expense of the overall height of the series structure (reducing its application potential in narrow space).

[0093] Test Example Six:

[0094] Taking Example 1 as an example, for low-temperature heat targets such as human body (people as a kind of constant temperature animal with high infrared ε, the apparent temperature is about 36℃), a single layer of low infrared emissivity top layer can already exhibit excellent thermal camouflage ability; specifically, after FC / Al-5 / 5 is sprayed on the surface of the butyronitrile glove by high-pressure air gun (15PSI) and worn for 60min, the average radiation temperature is stabilized at 25.1℃ (see Figure 15 ); compared with the temperature of the bare exposed part (38.1℃), FC / Al-5 / 5 effectively reduces the temperature difference between the human body and the environment, significantly changes the thermal infrared radiation characteristics of the human body, and can realize reliable infrared detection protection for the human heat source.

[0095] Test Example Seven:

[0096] Taking Example 1 as an example, for a static medium-temperature heat source of 80°C, the composite structure composed of BPCG-75 and FC / Al-5 / 5 can achieve effective stealth protection for the medium-temperature heat source from the perspectives of heat conduction and heat radiation. Specifically, after 120 minutes, the average surface temperature of the composite structure stabilized at around 63.9°C. After the infrared coating further attenuated the heat radiation, its average radiation temperature was only 41.4°C (see Figure 16 In addition, for dynamic medium-temperature heat sources with temperature fluctuations in the range of 45 to 80°C, the composite structure successfully suppressed temperature fluctuations by utilizing the temperature hysteresis generated by phase change behavior (the temperature fluctuation range can be reduced from 37.4°C to 19.6°C), and the fluctuation of radiation temperature was stabilized within 9.2°C (see Figure 17 ).

[0097] The stealth mechanism of the composite structure is as follows ​ As shown in the figure, BPCG-75, as a super absorber of heat, can fully absorb the heat of the heat conduction process by utilizing the phase change enthalpy (high thermal enthalpy of 152.6 kJ / kg), optimize the radiation bright spot of the single infrared coating in a medium-temperature environment, and increase the axial heat transfer resistance; at the same time, the layers of flaky Al powder in FC / Al-5 / 5 can reflect thermal radiation at multiple levels, achieving "thermal camouflage" of the apparent temperature.

[0098] Test Example 8:

[0099] Taking Example 1 as an example, for a static high-temperature heat source of 100°C, a stealth system composed of BPCG-75, P4, and FC / Al-5 / 5 can utilize polydimethylsiloxane resin with a thermal conductivity of only 0.15 W / m·K to effectively weaken the axial heat transfer in the structure, solving the camouflage weakness of single or two-by-two components during high-temperature stealth. The average radiation temperature after 10 hours is only 39.4°C (see ​ For dynamic high-temperature heat sources with temperatures fluctuating between 45 and 100°C, the stealth system effectively reduces the temperature increase by melting during the heating process and solidifying during the cooling process, utilizing its high phase change enthalpy. With the polydimethylsiloxane resin effectively slowing down the internal temperature response to external changes and the reliable thermal radiation attenuation of the infrared coating, the fluctuation of the radiant temperature is ultimately limited to a range of 8.6°C (see ​ ), the temperature fluctuation suppression rate is as high as 84.4%, which greatly reduces the exposure risk of dynamic thermal targets with high-frequency temperature changes.

[0100] The above embodiments are intended to illustrate the present invention, not to limit the present invention. Any solution that is a simple transformation of the present invention falls within the protection scope of the present invention.

Claims

1. A method for the preparation of integrated ordered structure materials, characterized by: The integrated ordered structure material comprises a high-enthalpy bottom layer and a low-infrared emissivity top layer arranged in sequence, the high-enthalpy bottom layer is a heat-stable gel layer immobilized with high-capacity phase change material, the low-infrared emissivity top layer is an infrared-transparent resin layer filled with metal fillers, and a high-thermal-resistance middle layer is arranged between the high-enthalpy bottom layer and the low-infrared emissivity top layer, the high-thermal-resistance middle layer is a polydimethylsiloxane resin layer; The method comprises the following steps: Step a) preparation of the high-enthalpy bottom layer: polyvinyl alcohol, fatty acid, acidic reagent and aldehyde crosslinking agent are sequentially mixed and reacted, and then a fatty acid-based phase change gel layer is obtained by solidification, washing and drying to serve as the high-enthalpy bottom layer; Step b) preparation of the high-thermal-resistance middle layer: dimethylsiloxane monomer and crosslinking agent are uniformly mixed and poured into a mold containing the high-enthalpy bottom layer, and then the mixed solution is solidified outside the high-enthalpy bottom layer to form the high-thermal-resistance middle layer; Step c) preparation of the low-infrared emissivity top layer: metal fillers are uniformly dispersed in an infrared-transparent resin base material, and then the dispersion is sprayed onto the outside of the high-thermal-resistance middle layer and solidified to form the low-infrared emissivity top layer.

2. The method of claim 1, wherein: The high-thermal-resistance middle layer is coated on all or part of the surface of the high-enthalpy bottom layer except the bottom surface, and the low-infrared emissivity top layer is coated on the top surface of the high-thermal-resistance middle layer.

3. The method of producing an integrated ordered structure material according to claim 2, wherein: The thickness of the high-thermal-resistance middle layer is controlled to be 3.0-5.0 mm, and the thickness of the low-infrared emissivity top layer is controlled to be 220-280 um.

4. The method of producing an integrated ordered structure material according to claim 3, wherein: The high-enthalpy bottom layer exhibits a progressive dense packing of worm-like rod structures, and the low-infrared emissivity top layer is in a layer-by-layer stacked form of metal fillers in the infrared-transparent resin layer.

5. The method of claim 1, wherein: In the step a), the loading amount of the fatty acid is 60-80 wt%, the mass-volume ratio of the fatty acid to the acidic reagent is 0.001-0.003 g / ul, the volume ratio of the acidic reagent to the aldehyde crosslinking agent is 6-10:1, the fatty acid is one or a combination of several of caproic acid, lauric acid, myristic acid, palmitic acid and stearic acid, the acidic reagent is hydrochloric acid, and the aldehyde crosslinking agent is one or a combination of several of formaldehyde, acetaldehyde, n-butyraldehyde, glutaraldehyde and crotonaldehyde.

6. The method of claim 1, wherein: In the step b), the mass ratio of the dimethylsiloxane monomer to the crosslinking agent is 8-12:

1.

7. The method of claim 1, wherein: In the step c), the loading amount of the metal fillers is 30-70 wt%, the metal fillers are one or a combination of several of aluminum powder, iron powder, zinc powder, silver powder and gold powder, the shape of the metal fillers is one or a combination of several of spherical, rod-like, flaky and irregular, the maximum distance between two points on the surface of the metal fillers is controlled to be 20-25 um, and the infrared-transparent resin is one or a combination of several of fluorocarbon resin, epoxy resin, polyurethane resin and acrylic resin.

8. Use of the integrated ordered structure material prepared by the method of any one of claims 1 to 4 in infrared stealth.

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