Radiative Cooling Coating with Dual-Polymer Emissivity
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Solution Overview
Problem
Current passive radiative cooling technologies are limited in their ability to effectively cool surfaces exposed to sunlight without consuming external energy, particularly in achieving significant temperature reductions below ambient levels.
Innovation Solution
A radiative cooling formulation comprising a binder with two polymers having non-overlapping emissivity peak values greater than 0.85 at wavelengths between 4 and 35 μm, combined with a solar reflector material that reflects solar radiation, embedded in a coating applied to various substrates, allowing for passive cooling without external energy input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional passive radiative cooling materials are used, then some cooling effect is achieved, but the temperature reduction below ambient levels is limited and insufficient for significant cooling applications
Solution Approach 1:
The patent employs a composite coating formulation combining multiple polymers with non-overlapping emissivity peaks, water-insoluble solar reflector particles, and a hydrophobic top layer. This composite structure enables simultaneous high solar reflectance and high infrared emissivity, achieving temperatures at least 5°C below ambient levels, thereby resolving the contradiction between achieving significant temperature reduction and maintaining reliable cooling effectiveness.
Solution Approach 2:
The coating is designed with spatially differentiated functional layers: a top hydrophobic layer for water repellency and a bottom polymer matrix with specific emissivity characteristics for thermal radiation. Each layer performs its specific function optimally, with the bottom layer providing high emissivity in the 8-13 μm atmospheric window while the top layer maintains solar reflectance, achieving reliable cooling under varied environmental conditions.
2Device complexity
If single polymer binders are used in radiative cooling coatings, then the coating structure is simple, but the net emissivity is insufficient to achieve significant cooling power
Solution Approach 1:
The patent uses a composite binder system with at least two different polymers, each contributing distinct emissivity peaks in the infrared spectrum. This multi-polymer approach creates a synergistic effect where the combined net emissivity exceeds that of individual polymers, enabling significant net cooling power while maintaining reasonable formulation complexity through a systematic combination of compatible polymer materials.
3Temperature
If coatings with high solar reflectance are used, then heating from solar radiation is reduced, but the ability to emit thermal radiation in the atmospheric window may be compromised
Solution Approach 1:
The coating structure separates solar reflection and thermal emission functions into different layers and wavelength ranges. The solar reflector particles (0.5-5 μm) handle solar radiation reflection, while the polymer binder matrix with its emissivity peaks in the 8-13 μm atmospheric window handles thermal radiation emission. This spectral and spatial separation allows both high solar reflectance and high thermal emission without compromise.
Solution Approach 2:
The composite formulation combines water-insoluble solar reflector particles with polymers having specific infrared emissivity characteristics. The particles provide solar reflectance while the polymer matrix provides high emissivity in the atmospheric window, creating a material that simultaneously reduces solar heating and enhances thermal radiation loss, resolving the contradiction between these two opposing requirements.
4Power
If coatings are designed for high emissivity in the atmospheric window, then radiative cooling is enhanced, but the coating may become more susceptible to water absorption and degradation
Solution Approach 1:
The coating is segmented into distinct functional layers: a bottom polymer matrix layer providing high emissivity for radiative cooling, and a top hydrophobic layer providing water repellency and environmental stability. This segmentation allows each layer to be optimized for its specific function without compromising the other, achieving both high radiative cooling power and improved durability.
Solution Approach 2:
The coating uses a composite structure combining emissive polymer materials with hydrophobic protective layers. The hydrophobic top layer (containing fluorinated or silane-based compounds) protects the underlying emissive layer from water absorption and environmental degradation, while allowing the emissive polymers to maintain their radiative cooling function, thus resolving the contradiction between cooling performance and durability.
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 solution achieves passive radiative cooling of at least 5 degrees Celsius below ambient temperature and provides net cooling power, effectively reducing surface temperatures through thermal radiation to the atmosphere, even under solar illumination, without requiring water or electricity.
Implementation Method 1
The radiative cooling formulation further includes a solar reflector material embedded in the binder
Implementation Method 2
Radiative cooling is the process by which an object loses heat by thermal radiation (e.g., electromagnetic radiation generated by thermal motion of charged particles in matter)
Implementation Method 3
The first polymer has a first emissivity peak value greater than 0.85 at a first wavelength between 4 and 35 micrometers (μm) and the second polymer has a second emissivity peak value greater than 0.85 at wavelengths between 4 and 35 μm
Data Source
AI summary
Disclosed herein in is a radiative cooling formulation including a first component with >55% reflectance in a wavelengths range of 0.3 to 2.5 microns, a second component with a first thermal emissivity peak value greater than 0.85 at a first wavelength in a range of 8 to 13 microns (μm), and a third component to mechanically bind together a mixture of the first component and second component.