Bilayer Radiative Cooling Coating for Color and Thermal Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing passive daytime radiative cooling (PDRC) solutions face limitations in achieving high cooling performance while maintaining color and scalability, as they often have high broadband visible reflectance, which is undesirable aesthetically and can cause eye safety issues, and current colored radiative coolers are either expensive or inefficient in infrared reflection.
Innovation Solution
A bilayer coating system comprising a thin colorant layer and a thicker scattering layer, where the scattering layer is made of porous polymers like poly(vinylidene fluoride-co-hexafluoropropene) or titanium dioxide, designed to backscatter near-infrared and short-wavelength infrared light, allowing for selective absorption of visible wavelengths and efficient radiative cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If broadband solar reflectance materials (white or metallized) are used to maximize radiative cooling, then cooling performance is improved, but aesthetic appearance and eye safety deteriorate due to strong white or silvery glares
Solution Approach 1:
The patent applies different optical properties to different wavelength regions: the coating selectively reflects near-infrared and short-wavelength infrared light (0.7-3.0 μm) while allowing visible light to pass through or be absorbed by the substrate. This creates local quality differentiation in the optical response, achieving high solar reflectance in thermal regions while maintaining aesthetic visible appearance and reducing harmful glare
Solution Approach 2:
The patent uses composite materials combining organic dyes or pigments with polymer matrices to achieve selective wavelength absorption. The composite structure enables the coating to absorb specific visible wavelengths for coloration while the underlying substrate provides infrared reflection, combining multiple material properties to resolve the contradiction between cooling performance and aesthetic/eye safety requirements
2Ease of manufacture
If colored paints based on TiO2 particles and dye mixtures are used to achieve color and scalability, then manufacturing ease and scalability are improved, but infrared and ultraviolet absorption increases causing the coating to become hot under sunlight
Solution Approach 1:
The patent segments the coating into distinct functional layers: a top colorant layer containing dyes or pigments for visible wavelength absorption and coloration, and a underlying scattering layer for infrared reflection. This segmentation allows each layer to perform its specific function optimally - the colorant layer provides scalability and color while the scattering layer provides infrared reflection to prevent overheating
Solution Approach 2:
The patent introduces a scattering layer as an intermediary between the colorant layer and the substrate. This intermediary layer backscatters infrared and ultraviolet radiation, preventing the colorant layer from absorbing excessive thermal radiation. The scattering layer acts as a mediator that protects the color-providing materials from overheating while maintaining the scalability of paint-based application methods
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The bilayer coating achieves significant infrared reflectance and temperature reduction under sunlight, maintaining color appearance and scalability, outperforming monolayer commercial paints in radiative cooling efficiency with minimal absorption of infrared radiation.
Implementation Method 1
the scattering layer configured to backscatter solar wavelengths of near infrared light and short-wavelength infrared light
Implementation Method 2
the colorant layer configured to selectively absorb one or more wavelengths of visible light
Implementation Method 3
Passive daytime radiative cooling (PDRC), a phenomenon where a surface reflects sunlight and radiates heat through the long wavelength infrared (LWIR) atmospheric window into the cold outer space
Data Source
AI summary
A coating including a relatively thin visible-absorptive layer atop a relatively thick non-absorptive, solar-scattering underlayer. The thin top layer enables efficient absorption of appropriate visible wavelengths to show specific colors, and minimizes absorption in the infrared radiation in sunlight due to its relatively small thickness. Meanwhile, the bottom layer maximizes the backscattering of infrared light without absorption to reduce solar heating.