Thin films including nanoparticles with solar reflectance properties for building materials
Disclosed are solar-reflective building materials, including roofing articles, that include nanoparticle-containing thin films; such articles display high reflectance of near-infrared radiation and high transmission of radiation in the visible light range so as to reduce the heat island effects experienced by the articles while also maintaining an aesthetically pleasing appearance. Also disclosed are related methods of fabricating such articles.
1. A roofing article, comprising:
an essentially opaque substrate at least partially surmounted by at least one thin film having an average thickness in the range of from about 20 nm to about 500 nm,
the at least one thin film comprising at least one population of nanoparticles residing in a matrix,
the matrix having a first refractive index,
the at least one population of nanoparticles having a second refractive index,
at least one of the population of nanoparticles having at least one characteristic dimension in the range of from about 10 nm to about 500 nm,
the at least one thin film transmitting at least about 5% of radiation having a wavelength of between about 300 nm and about 700 nm, and
the at least one thin film reflecting at least about 20% of radiation having a wavelength of between about 700 nm and about 2500 nm.
2. The roofing article of claim 1 , wherein the roofing article has an emissivity of at least about 75% for radiation having a wavelength in the range of greater than about 2500 nm.
3. The roofing article of claim 1 , wherein the at least one thin film absorbs less than about 60% of radiation having a wavelength of between about 300 nm and 2500 nm.
4. The roofing article of claim 1 , wherein the matrix comprises a polymer, silica, a silicate, a phosphate, or any combination thereof.
5. The roofing article of claim 1 , wherein the combination of the thin film's percentage transmission of radiation having a wavelength of between about 300 nm and about 700 nm and the thin film's percentage reflectance of radiation having a wavelength of between about 700 nm and about 2500 nm is greater than 50%.
6. The roofing article of claim 1 , wherein a nanoparticle is characterized as being spherical, cylindrical, oblong, ovoid, acicular, cubic, hollow, polygonal or any combination thereof.
7. The roofing article of claim 1 , wherein a nanoparticle comprises a high-index material, a metal, a metal oxide, a conducting material, a semiconducting material, or any combination thereof.
8. The roofing article of claim 7 , wherein the metal comprises aluminum, silver, gold, or any combination thereof.
9. The roofing article of claim 7 , wherein the nanoparticle comprises LaB 6 , a metal oxide selected from the group consisting of SnO 2 :F, In 2 O 3 :Sn, ZnO:Al, or any combination thereof.
10. The roofing article of claim 7 , wherein the high-index material comprises TiO 2 , Fe 2 O 3 , or any combination thereof.
11. The roofing article of claim 7 , wherein the high-index material comprises a material having a refractive index of at least about 2.
12. The roofing article of claim 1 , wherein the difference between the first refractive index and the second refractive index is at least about 1.
13. The roofing article of claim 1 , wherein the roofing article has an L* value of less than about 65.
14. The roofing article of claim 1 , wherein the roofing article comprises a sealant, an algaecide, a biocide, or my combination thereof.
15. A method of fabricating a building material, comprising:
disposing onto at least a portion of an essentially opaque substrate at least one thin film having an average thickness in the range of from about 20 nm to about 500 nm,
the at least one thin film comprising at least one matrix and a population of nanoparticles,
at least one nanoparticle having at least one average characteristic dimension in the range of from about 10 nm to about 500 nm,
the at least one thin film transmitting from about 5% to about 100% of radiation having a wavelength of between about 300 nm and about 700 nm,
the at least one thin film reflecting at least about 20% of radiation having a wavelength of between about 700 nm and about 2500 nm.
16. The method of claim 15 , wherein the at least one film is disposed onto the upper surface of the substrate by spraying, sol-gel spraying, electrospraying, laminating, fluidized bed processing, or any combination thereof.
17. The method of claim 15 , wherein the disposing of the at least one thin film onto the upper surface of the substrate is performed at less than about 100° C.
18. A roofing article, comprising:
an essentially opaque substrate at least partially surmounted by a thin film having an average thickness in the range of from about 20 nm to about 500 nm,
the at least one thin film comprising a matrix and at least one population of nanoparticles,
at least one of the population of nanoparticles having at least one characteristic dimension in the range of from about 10 nm to about 500 nm,
the at least one thin film transmitting at least about 5% of radiation having a wavelength of between about 300 nm and about 700 nm, and
the at least one thin film reflecting at least about 20% of radiation having a wavelength of between about 700 nm and about 2500 nm.
19. The roofing article of claim 18 , wherein the roofing article has an emissivity of at least about 75% for radiation having a wavelength of at least about 2500 nm.
20. A method of fabricating a roofing article, comprising:
spraying a sol onto at least a portion of a shingle,
the sol comprising a matrix and at least one population of nanoparticles,
at least one of the population of nanoparticles having at least one characteristic dimension in the range of from about 10 nm to about 500 nm,
processing the sol to give rise to a thin film having a thickness in the range of from about 50 nm to about 200 nm,
the at least one thin film transmitting at least about 5% of radiation having a wavelength of between about 300 nm and about 700 nm, and
the at least one thin film reflecting at least about 20% of radiation having a wavelength of between about 700 nm and about 2500 nm.
21. The method of claim 20 , wherein the roofing article has an emissivity of at least about 75% for radiation having a wavelength of at least about 2500 nm.
22. An opaque building material, comprising:
an essentially opaque substrate at least partially surmounted by at least one thin film having an average thickness in the range of from about 20 nm to about 500 nm,
the at least one thin film comprising at least one population of nanoparticles residing in a matrix,
at least one of the population of nanoparticles having at least one characteristic dimension in the range of from about 10 nm to about 500 nm,
the at least one thin film transmitting at least about 5% of radiation having a wavelength of between about 300 nm and about 700 nm, and
the at least one thin film reflecting at least about 20% of radiation having a wavelength of between about 700 nm and about 2500 nm.
23. The opaque building material of claim 22 , wherein the opaque building material is selected from the group consisting of roofing materials, siding materials, fencing materials, rail materials, and decking materials.
24. The opaque building material of claim 22 , wherein the opaque building material has an emissivity of at least about 75% for radiation having a wavelength of greater than about 2500 nm.
25. The roofing article of claim 18 , wherein the thin film has an average thickness in the range of from about 200 nm to about 500 nm.
26. The roofing material of claim 22 , wherein the thin film has an average thickness in the range of from about 200 nm to about 500 nm.
27. The roofing material of claim 1 , wherein the thin film at least partially surmounts one or more granules.
28. The roofing material of claim 18 , wherein the thin film at least partially surmounts one or more granules.
29. The roofing article of claim 18 , further comprising a sealant, an algaecide, a biocide, or my combination thereof.
30. The opaque building material of claim 22 , further comprising a sealant, an algaecide, a biocide, or my combination thereof.