Chromogenic radiative cooling element

Abstract

The present invention relates to a chromogenic radiative cooling element comprising a liquid crystal layer including a cholesteric liquid crystal that includes a reactive mesogen compound and a chiral dopant and has a pitch in the range of 50 nm to 550 nm, thus maintaining excellent cooling performance while producing various colors.

Description

Chromatic radiant cooling device

[0001] The present invention relates to a chromogenic radiant cooling device that implements various colors and exhibits cooling performance without external power.

[0002] Cooling requires energy consumption. Current refrigeration devices like refrigerators and air conditioners use electrical energy to compress a refrigerant, then absorb the heat generated when the compressed refrigerant expands to achieve cooling. In contrast, radiant cooling technology can achieve cooling without consuming energy.

[0003] Radiative cooling requires independent control of light absorption, reflection, and emission across each wavelength. In most cases, the heat source is incident sunlight. Sunlight heat is distributed across the UV, visible, and near-infrared wavelength ranges. Reflecting light in these wavelengths can block or dissipate heat from sunlight.

[0004] For heat dissipation, it must be able to radiate heat well into space by having high absorption or emissivity in the long-wave infrared region.

[0005] According to the Planck distribution, when the temperature is 300 K, the maximum heat dissipation condition is in the wavelength range of 6-20 ㎛. In the case of Earth, the atmospheric window area is approximately 8-13 ㎛, so in order to maximize the heat dissipation ability of a passive cooling element, the absorption or emissivity must be at its maximum in the 8-13 ㎛ area.

[0006] Infrared radiation in the window wavelength range of the atmosphere plays a key role in achieving radiative cooling by actual heat dissipation. If the wavelength range of the atmosphere can reflect 100% of the incident sunlight (radiated from the sun) in the ultraviolet-visible-near infrared range and radiate 100% of the long-wavelength infrared in the 8-13㎛ range of the window region of the atmosphere to the outside, the power output would be 158 W / m at an ambient temperature of 300 K. 2 The cooling performance can be implemented without energy consumption.

[0007] In addition, radiant cooling elements can be used in automobiles, buildings, containers, etc. to reduce the energy burden required for cooling. However, in order to implement color, only light of a specific wavelength must be reflected for color expression, and the light of the remaining wavelengths must be prevented from being absorbed for cooling. However, conventional radiant cooling elements are made of metal that can have high sunlight reflection, and they reflect light of a specific wavelength and absorb light of the remaining wavelengths, which is transmitted to the internal object and acts to increase the temperature of the object. If even a part of the sunlight is absorbed by the internal object, it is difficult to provide cooling performance in a temperature range lower than the atmospheric temperature. Therefore, conventional radiant cooling elements had a limitation in that they could not achieve both color expression and cooling performance at the same time.

[0008] The problem to be solved by the present invention is to provide a chromogenic radiant cooling device having excellent cooling performance while realizing various colors even under sunlight.

[0009] According to one embodiment of the present invention, a chromogenic radiative cooling device is provided, which includes a liquid crystal layer comprising a cholesteric liquid crystal having a pitch range of 50 nm to 550 nm, and which includes a reactive mesogenic compound and a chiral dopant.

[0010] The mesogenic compound is characterized by being represented by any one of the following chemical formulas 1 to 4.

[0011] [Chemical Formula 1]

[0012]

[0013] [Chemical Formula 2]

[0014]

[0015] [Chemical Formula 3]

[0016]

[0017] [Chemical Formula 4]

[0018]

[0019] The chromogenic radiant cooling element is characterized by further including a protective film layer formed on top of the liquid crystal layer.

[0020] The protective film layer of the chromogenic radiant cooling element is characterized by being made of a polymer or an inorganic material.

[0021] The polymer is characterized by including at least one of PDMS (Polydimethyl siloxane), PMMA (Poly(methyl methacrylate)), PVDF (Polyvinylidene fluoride), PUA (Poly urethane acrylate), PET (polyethylene terephthalate), PVC (polyvinyl chloride), and DPHA (Dipentaerythritol Hexaacrylate).

[0022] The inorganic material is characterized by including at least one of SiO2, Al2O3, Ta2O5, CaSO4, MgHPO4, ZrO2, BaSO4, AlPO4, HfO2, and Y2O3.

[0023] The chromogenic radiative cooling element is characterized by further including a reflective layer formed under the liquid crystal layer.

[0024] The reflective layer is characterized by including at least one of gold (Au), copper (Cu), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), silver (Ag), aluminum (Al), and platinum (Pt).

[0025] The chromogenic radiant cooling element is formed under the reflective layer and is characterized by further including a substrate layer made of any one of a Si wafer, glass, and PET (polyethylene terephthalate) film.

[0026] The chromogenic radiative cooling element is characterized by further including a transparent layer formed under the liquid crystal layer.

[0027] The transparent layer is characterized by being made of one of glass, PET (polyethylene terephthalate), and ITO (indium tin oxide).

[0028] According to one embodiment of the present invention, a chromogenic radiative cooling device including a liquid crystal layer comprising a cholesteric liquid crystal having a pitch range of 50 nm to 550 nm, and including a reactive mesogenic compound and a chiral dopant, can maintain excellent cooling performance while implementing various colors, and thus can be applied to buildings, electronic devices, etc. that require both cooling and aesthetics.

[0029] The effects of the present invention are not limited to the effects described above, and effects not mentioned will be clearly understood by those skilled in the art from the present specification and the attached drawings.

[0030] FIG. 1(a) to FIG. 1(g) are drawings illustrating a chromogenic radiant cooling element according to one embodiment of the present invention.

[0031] FIG. 2 is a conceptual diagram of a cholesteric liquid crystal included in a liquid crystal layer according to one embodiment of the present invention.

[0032] Figure 3 is an SEM image of a cross-section of a chromogenic radiant cooling element according to Example 1.

[0033] Figure 4 is a UV-Vis diffuse reflectance spectrum of a chromogenic radiant cooling device according to Example 1.

[0034] Figures 5(a) to (c) are images showing the color development of the cooling elements for Examples 1, 3, and 4, respectively.

[0035] Figure 6 is a graph showing the infrared absorption and emissivity of the chromogenic radiant cooling element according to Example 1.

[0036] Figure 7 is a graph illustrating an experiment on daytime external temperature change in an outdoor environment for Examples 1, 2 and Comparative Example 1.

[0037] The specific details for implementing the present invention will be described in detail with reference to the attached drawings below.

[0038] When a part of this specification is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0039] Throughout this specification, when it is said that an element is "on" another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0040] Throughout the present specification, cholesteric liquid crystal means a chiral nematic liquid crystal formed by adding a chiral dopant or a photo-sensitive chiral dopant that induces a periodic spiral structure to a nematic liquid crystal, and an additive such as a photoinitiator may be additionally included during the formation process.

[0041] Figures 1(a) to 1(g) schematically illustrate the structure of a chromogenic radiant cooling element according to one embodiment of the present invention. The structure of the chromogenic radiant cooling element is supplementarily described below using Figures 1(a) to 1(g).

[0042] FIG. 1(a) is a schematic diagram showing a chromogenic radiant cooling element including a liquid crystal layer (110) according to one embodiment of the present invention.

[0043] One embodiment of the present invention provides a chromogenic radiative cooling device comprising a liquid crystal layer including a cholesteric liquid crystal having a pitch range of 50 nm to 550 nm, and including a reactive mesogenic compound and a chiral dopant.

[0044] Figure 1(a) illustrates a structure in which a chromogenic radiation cooling element (100) according to one embodiment of the present invention is formed as a single liquid crystal layer (110) structure.

[0045] FIG. 2 is a conceptual diagram of a cholesteric liquid crystal included in a liquid crystal layer (110) according to one embodiment of the present invention. Specifically, it shows that both left-handed and right-handed orientations can be implemented by controlling the alignment direction. Cholesteric liquid crystals can express colors through light reflected by the pitch of their spiral structure, and can control the colors expressed by absorbing and emitting different colors depending on the type of the photoreactive mesogenic compound constituting them, the type and concentration of the chiral dopant, and external stimuli.

[0046] In addition, the wavelength of the reflected light is determined by the pitch (p) of the cholesteric liquid crystal, and the longer the peak, the more the long wavelength of the red series is reflected, and the shorter the pitch, the more the short wavelength of the blue series is reflected. In addition, by adjusting the pitch of the cholesteric liquid crystal, the wavelength of the green series near 550 nm among visible light can be reflected, and the cholesteric liquid crystal according to an embodiment of the present invention can implement a variety of desired colors by having a pitch range of 50 nm to 550 nm. Therefore, the chromogenic radiative cooling device according to an embodiment of the present invention can implement a variety of colors by including a liquid crystal layer including cholesteric liquid crystal, and can implement colors clearly even under sunlight by diffusing and reflecting light.

[0047] According to one embodiment of the present invention, the reactive mesogenic compound may be represented by any one of the following chemical formulas 1 to 4, but is not limited thereto.

[0048]

[0049] [Chemical Formula 1]

[0050]

[0051] [Chemical Formula 2]

[0052]

[0053] [Chemical Formula 3]

[0054]

[0055] [Chemical Formula 4]

[0056]

[0057]

[0058] Specifically, the mesogenic compounds represented by Chemical Formulas 1 to 4 contain a large number of functional groups such as CO, COC, CF, or CH that absorb / emit infrared rays in the atmospheric transmission layer wavelength range (8 ㎛ to 13 ㎛), and thus have high absorption or emissivity in the infrared region, thereby exhibiting excellent cooling properties. In addition, since mesogens have isomer properties, the color and temperature can be controlled by controlling phase change, transmission, scattering, and reflection by changing the content, and the color can be clearly expressed even under sunlight by diffusing and reflecting light.

[0059] A chiral dopant according to one embodiment of the present invention can be selected depending on the color to be implemented, and examples thereof include, but are not limited to, LC756 and S-811.

[0060] Referring to FIG. 1(b), a chromogenic radiant cooling element (100) according to one embodiment of the present invention may further include a protective film layer (130) formed on top of a liquid crystal layer (110). Specifically, by including the protective film layer, physical or chemical degeneration of the liquid crystal layer can be prevented, and it can play a role in supporting infrared absorption and radiation of the liquid crystal layer.

[0061] According to one embodiment of the present invention, the protective film layer may be composed of a polymer or an inorganic material. Specifically, by being composed of a polymer or an inorganic material, it can absorb and radiate infrared rays, thereby enhancing radiative cooling performance.

[0062] According to one embodiment of the present invention, the polymer may be at least one of PDMS (Polydimethyl siloxane), PMMA (Poly(methyl methacrylate)), PVDF (Polyvinylidene fluoride), PUA (Poly urethane acrylate), PET (polyethylene terephthalate), PVC (polyvinyl chloride), and DPHA (Dipentaerythritol Hexaacrylate). Since the polymer has high emissivity for all infrared wavelengths, the radiative cooling performance may be superior.

[0063] According to one embodiment of the present invention, the inorganic material may include at least one of SiO2, Al2O3, Ta2O5, CaSO4, MgHPO4, ZrO2, BaSO4, AlPO4, HfO2, and Y2O3. Since the polymer has high emissivity for all infrared wavelengths, the radiation cooling performance may be superior.

[0064] Referring to FIG. 1(c), a chromogenic radiation cooling element according to one embodiment of the present invention may further include a reflective layer (150) formed under a liquid crystal layer (110). Specifically, the reflective layer is formed under the liquid crystal layer to additionally reflect infrared rays transmitted without being reflected by the liquid crystal layer, thereby improving cooling performance.

[0065] According to one embodiment of the present invention, the reflective layer may include at least one of gold (Au), copper (Cu), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), silver (Ag), aluminum (Al), and platinum (Pt). Specifically, since the reflective layer is a specular metal, it can more easily reflect infrared rays that are not reflected by the liquid crystal layer, thereby improving cooling performance.

[0066] Referring to FIG. 1(d) or FIG. 1(e), a chromogenic radiation cooling element (100) according to one embodiment of the present invention may further include a substrate layer (170) formed under a reflective layer (150) and made of any one of a Si wafer, glass, and a PET (polyethylene terephthalate) film. By including the substrate layer, the durability of the chromogenic radiation cooling element manufactured may be improved.

[0067] Referring to FIG. 1(f) or FIG. 1(g), a chromogenic radiation cooling element according to one embodiment of the present invention may further include a transmission layer (190) formed under a liquid crystal layer (110).

[0068] According to one embodiment of the present invention, the transparent layer may be formed of any one of glass, polyethylene terephthalate (PET), and indium tin oxide (ITO). In addition, since the transparent layer is formed of a transparent material, it can form a transparent element whose interior is visible by transmitting a portion of light.

[0069] Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. However, these embodiments are intended to illustrate the present invention more specifically, and it will be apparent to those skilled in the art that the scope of the present invention is not limited thereby.

[0070]

[0071] Example 1

[0072] A mesogenic compound (LC242, Daken Chemical), a chiral dopant (ISO(6OBA)2, 4-Chem Lab.), a photoinitiator (2,2-dimethoxy-2-phenylacetophenone, Sigma-Aldrich), and xylene (0.44 g) were added to a 10 ml flat-bottom vial equipped with a stirring bar. The weight ratio of the mesogenic compound, the chiral dopant, and the photoinitiator varied from 94.8:5.2:1 to 92.8:7.2:1 depending on the color, and the total weight was maintained at 1 g. The mixed solution was heated at 110°C for 2 hours while stirring to prepare a composition for a liquid crystal film. This was applied to a silicon wafer having a laminated reflector made of aluminum metal, spin-coated at 500 rpm for 4 seconds, and then spin-coated at 9000 rpm for 40 seconds. After leaving it in a drying oven at 80℃ for 2 minutes, it was cured with UV at 85℃ in a nitrogen atmosphere for 15 minutes to form a liquid crystal layer with a thickness of approximately 5㎛.

[0073]

[0074] Example 2

[0075] A 100 μm thick protective film layer made of PDMS was additionally laminated on top of the liquid crystal layer of Example 1.

[0076]

[0077] Example 3

[0078] It was manufactured in the same manner as Example 2 except that the silicon wafer layer was removed in Example 2.

[0079]

[0080] Example 4

[0081] A mesogenic compound (LC242, Daken Chemical), a chiral dopant (ISO(6OBA)2, 4-Chem Lab.), a photoinitiator (2,2-dimethoxy-2-phenylacetophenone, Sigma-Aldrich), and xylene (0.44 g) were added to a 10 ml flat-bottom vial equipped with a stirring bar. The weight ratio of the mesogenic compound, the chiral dopant, and the photoinitiator varied from 94.8:5.2:1 to 92.8:7.2:1 depending on the color, and the total weight was maintained at 1 g. The mixed solution was stirred and heated at 110°C for 2 hours to prepare a composition for a liquid crystal film. This was applied to a glass substrate, spin-coated at 500 rpm for 4 seconds, and then spin-coated at 9000 rpm for 40 seconds. After leaving it in a drying oven at 80°C for 2 minutes, UV was applied to 85 o C, a liquid crystal layer of approximately 5 μm thickness was formed by curing for 15 minutes in a nitrogen atmosphere.

[0082]

[0083] Comparative Example 1

[0084] Control samples were prepared from JEVISCO Co. using commercial radiant cooling paints: red-orange (SD 1147), green (TN 0349), and blue (CL 1124). Two milligrams of each paint was applied undiluted to a silicon wafer coated with a reflector made of aluminum metal. The wafer was spin-coated at 500 rpm for 5 s and then at 2000 rpm for 20 s to form a 200 μm-thick layer. The applied paint layers were allowed to air-dry overnight at room temperature (25°C).

[0085]

[0086] Characteristic evaluation

[0087] Fig. 3 is a SEM image of a cross-section of a chromogenic radiative cooling element according to Example 1. Referring to Fig. 3, it can be confirmed that colors can be implemented depending on the pitch size of the cholesteric liquid crystal.

[0088] Fig. 4 is a UV-Vis diffuse reflection spectrum of a chromogenic radiant cooling device according to Example 1. Referring to Fig. 4, it can be confirmed that diffuse reflection is possible for all colors of red, green, and blue because the liquid crystal layer includes a cholesteric liquid crystal having a curved shape.

[0089] FIGS. 5(a) to 5(c) are images showing the color development of the cooling elements for Examples 1, 3, and 4, respectively. Referring to FIG. 5, it can be confirmed that the manufactured color-developing radiant cooling element is not limited to the opaque shape of Example 1 or Example 3 and the translucent shape of Example 4, and can implement various colors from blue to red. In particular, referring to FIG. 5(b), it can be confirmed that the color-developing radiant cooling element manufactured according to Example 3 has excellent flexibility and maintains color development performance even when bent.

[0090] Figure 6 is a graph showing the infrared absorption and emissivity of the chromogenic radiant cooling element according to Example 1. Specifically, it can be confirmed that it has high absorption and emissivity in the long-wavelength infrared region of 8 μm to 13 μm, which corresponds to the window of the atmosphere.

[0091] Figure 7 is a graph illustrating an experiment on external temperature changes during the day in an outdoor environment for Examples 1, 2, and Comparative Example 1, and was measured on June 3, 2023. Referring to Figure 7, it can be confirmed that both Examples 1 and 2 exhibit temperatures that are up to 30 degrees lower than Comparative Example 1, thereby confirming excellent cooling performance.

Claims

1. Contains a reactive mesogenic compound and a chiral dopant, A chromogenic radiative cooling device comprising a liquid crystal layer comprising cholesteric liquid crystals having a pitch range of 50 nm to 550 nm.

2. In paragraph 1, A chromogenic radiant cooling device characterized in that the reactive mesogenic compound is represented by one of the following chemical formulas 1 to 4. [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 3] [Chemical Formula 4] 3. In paragraph 1, A chromogenic radiant cooling element characterized in that it further includes a protective film layer formed on the upper portion of the liquid crystal layer.

4. In paragraph 3, A chromogenic radiant cooling element characterized in that the above protective film layer is made of a polymer or an inorganic material.

5. In paragraph 4, A chromogenic radiant cooling element characterized in that the polymer comprises at least one of PDMS (Polydimethyl siloxane), PMMA (Poly(methyl methacrylate)), PVDF (Polyvinylidene fluoride), PUA (Poly urethane acrylate), PET (polyethylene terephthalate), PVC (polyvinyl chloride), and DPHA (Dipentaerythritol Hexaacrylate).

6. In paragraph 4, A chromogenic radiant cooling element characterized in that the inorganic material comprises at least one of SiO2, Al2O3, Ta2O5, CaSO4, MgHPO4, ZrO2, BaSO4, AlPO4, HfO2, and Y2O3.

7. In paragraph 1, A chromogenic radiative cooling device characterized by further comprising a reflective layer formed under the liquid crystal layer.

8. In paragraph 7, A chromogenic radiant cooling element characterized in that the above reflective layer comprises at least one of gold (Au), copper (Cu), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), silver (Ag), aluminum (Al), and platinum (Pt).

9. In paragraph 7, A chromogenic radiant cooling element characterized in that it further includes a substrate layer formed under the above reflective layer and made of any one of a Si wafer, glass, and PET (polyethylene terephthalate) film.

10. In paragraph 1, A chromogenic radiative cooling device characterized by further comprising a transparent layer formed under the liquid crystal layer.

11. In paragraph 10, A chromogenic radiant cooling element characterized in that the above-mentioned transparent layer is made of any one of glass, PET (polyethylene terephthalate), and ITO (indium tin oxide).

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