HIGH MODULUS, HIGH THERMAL CONDUCTIVITY BILAYER RADIATIVE PASSIVE COOLANT
A polymer bilayer includes a layer of a porous fluoropolymer directly overlying a layer of polyethylene. The polyethylene layer may be porous or dense and may include an ultra-high molecular weight polymer. The polymer bilayer may be co-integrated with structures (e.g., wearable devices) exposed to high thermal loads (>0-1000 W/m 2 ) and provide passive cooling thereof. For instance, passive cooling of AR/VR glasses under different solar loads may be achieved by a polymer bilayer that is both highly reflective across solar heating wavelengths and highly emissive in the long-wavelength infrared. The high reflectance decreases energy absorption across the solar spectrum while the high emissivity promotes radiative heat transfer to the surroundings.
1 . A polymer bilayer comprising:
a first layer comprising a porous fluoropolymer; and
a second layer comprising polyethylene overlying the first layer.
2 . The polymer bilayer of claim 1 , having a short wavelength (0.25<λ<5 μm) infrared reflectance of at least approximately 10%, and a long wavelength (8<λ<14 μm) infrared reflectance of less than approximately 10%.
3 . The polymer bilayer of claim 1 , wherein the first layer comprises a non-porous fluoropolymer support layer directly overlying the porous fluoropolymer.
4 . The polymer bilayer of claim 1 , wherein the porous fluoropolymer comprises polyvinylidene fluoride (PVDF).
5 . The polymer bilayer of claim 1 , wherein the porous fluoropolymer is selected from the group consisting of PVDF-CTFE, PVDF-HFP, PVDF-TFE, PVDF-TrFE, PVDF-TrFE-TFE, and combinations thereof.
6 . The polymer bilayer of claim 1 , wherein the porous fluoropolymer comprises a porosity of at least approximately 15 vol. %.
7 . The polymer bilayer of claim 1 , wherein the porous fluoropolymer comprises pores having an average pore size of at least approximately 100 nm.
8 . The polymer bilayer of claim 1 , wherein the polyethylene comprises a molecular weight of at least approximately 300,000 g/mol.
9 . The polymer bilayer of claim 1 , wherein the second layer comprises a low molecular weight wax.
10 . The polymer bilayer of claim 1 , wherein the second layer is substantially dense.
11 . The polymer bilayer of claim 1 , wherein the second layer comprises a porosity of at least approximately 1 vol. %.
12 . The polymer bilayer of claim 1 , wherein the second layer comprises pores having an average pore size of at least approximately 50 nm.
13 . The polymer bilayer of claim 1 , wherein the second layer comprises an additive selected from the group consisting of an antioxidant and a pigment.
14 . The polymer bilayer of claim 1 , wherein the second layer comprises a thermal conductivity of at least approximately 5 W/mK.
15 . The polymer bilayer of claim 1 , wherein the second layer comprises a Young's modulus of at least approximately 2 GPa and a tensile strength of at least approximately 0.7 GPa.
16 . The polymer bilayer of claim 1 , wherein the porous fluoropolymer and the polyethylene each have a solar spectrum reflectance of at least approximately 40%.
17 . The polymer bilayer of claim 1 , wherein the porous fluoropolymer and the polyethylene each have a long wavelength infrared emissivity of at least approximately 40%.
18 . The polymer bilayer of claim 1 , wherein a thickness of the first layer ranges from approximately 0.2 mm to approximately 1 mm and a thickness of the second layer ranges from approximately 10 micrometers to approximately 1 mm.
19 . A polymer bilayer comprising:
a first layer comprising a porous fluoropolymer; and
a second layer comprising ultra-high molecular weight polyethylene directly overlying the first layer.
20 . A method comprising:
forming a first layer comprising a porous fluoropolymer;
forming a second layer comprising polyethylene having a molecular weight of at least approximately 300,000 g/mol; and
laminating the first layer to the second layer to form a polymer bilayer having a short wavelength (0.25<λ<5 μm) infrared reflectance of at least approximately 10% and a long wavelength (8<λ<14 μm) infrared reflectance of less than approximately 10%.