Radiative Cooling Coating with Dual-Polymer Emissivity
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Solution Overview
Problem
Current passive radiative cooling technologies face challenges in effectively cooling 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, which reflects solar radiation and enhances thermal emissivity, 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 cooling can be achieved without external energy, but the temperature reduction below ambient levels is limited
Solution Approach 1:
The patent employs a composite coating formulation combining multiple polymers with non-overlapping emissivity peaks and solar reflector materials. This composite structure enables simultaneous high solar reflectance and enhanced infrared emissivity, achieving significant temperature reductions (up to 10°C below ambient) while maintaining net cooling power through synergistic material interaction.
Solution Approach 2:
The patent utilizes polymers with specifically engineered emissivity parameters, achieving peak emissivity values greater than 0.85 at non-overlapping wavelengths between 4-35 μm. By optimizing these spectral parameters and combining them with solar reflector materials having reflectance greater than 0.95, the coating achieves enhanced net cooling power while maintaining practical water insolubility.
2Temperature
If solar reflector material is added to enhance cooling, then thermal emissivity improves, but the complexity of the coating formulation increases
Solution Approach 1:
The patent merges solar reflector materials with polymer binders in a single coating formulation, where the solar reflector particles are embedded within the polymer matrix. This integration allows simultaneous achievement of high solar reflectance and thermal emissivity without requiring separate layers or complex multi-component systems, thereby reducing overall formulation complexity.
Solution Approach 2:
The polymer binder serves multiple functions: it provides structural integrity, ensures practical water insolubility, contributes to non-overlapping emissivity peaks, and embeds solar reflector materials. This multi-functionality reduces the need for additional separate components, simplifying the overall coating formulation while maintaining enhanced thermal emissivity.
3Loss of energy
If multiple polymers with non-overlapping emissivity peaks are used, then net emissivity increases, but the manufacturing precision requirements increase
Solution Approach 1:
The patent selects polymers with inherently non-overlapping emissivity peak wavelengths, such as polyvinyl butyral (PVB) with a peak at 7.2 μm and polyethyl methacrylate (PEMA) with a peak at 9.7 μm. This parameter selection approach ensures net emissivity greater than individual polymers while avoiding the need for precise peak alignment during manufacturing, as the non-overlapping characteristics are intrinsic to the material choices.
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 formulation achieves passive radiative cooling of up to 10 degrees Celsius below ambient temperature during the day and provides net cooling power, reducing the temperature of surfaces by emitting more thermal energy than absorbed, without requiring water or electricity.
Implementation Method 1
a solar reflector material embedded in the binder... the solar reflector material reflects solar radiation at wavelengths from 0.3 to 2.5 μm
Implementation Method 2
Radiative cooling is the process by which an object loses heat by thermal radiation... The first polymer has a first emissivity peak value greater than 0.85 at a first wavelength between 4 and 35 micrometers (m)
Data Source
AI summary
Disclosed herein in is a radiative cooling formulation including a solvent for providing a viscosity of a radiative cooling material for application onto a surface to be passively cooled. The radiative cooling formulation includes a binder for the radiative cooling material's integrity and bonding to the surface to be passively cooled. The radiative cooling formulation includes a polymer, which, in combination with the binder, provides one or more properties in the radiative cooling material, including a reflectance of or greater than 55% in a wavelengths range of 0.3 to 2.5 microns and a first thermal emissivity peak value greater than 0.85 at a first wavelength in a range of 8 to 13 microns (μm). For example, the polymer is a latex material including a styrene based copolymer.