# US 11,999,152 B2 · Passive thermal management using thermoresponsive hydrogel

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- Number: US 11,999,152 B2
- Document ID: US11999152B2
- Status: Granted
- Kind: B2
- Application number: 17/554,177
- Filed: 2021-12-17
- Published: 2023-06-22
- Granted: 2024-06-04
- Earliest claimed: 2021-12-17
- Assignees: Toyota Motor Engineering & Manufacturing North America, Inc.; The Board of Trustees of the University of Illinois
- Applicants: Toyota Motor Engineering & Manufacturing North America, Inc; The Board of Trustees of the University of Illinois
- Inventors: Shailesh N. Joshi; Dajie Xie; Paul Braun
- Web page: https://patentgrep.com/patent/US11999152B2

## CPC

- B32B 5/18: characterised by features of a layer {of} foamed material
- F28F 13/18: by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing
- B32B 3/04: characterised by {at least one} layer folded at the edge, e.g. over another layer {; characterised by at least one layer enveloping or enclosing a material}
- B32B 5/32: {at least two} layers being foamed {and next to each other}
- B32B 9/007: {comprising carbon, e.g. graphite, composite carbon}
- B32B 27/32: comprising polyolefins {(comprising vinyl (co)polymers or acrylic (co)polymers B32B27/30)}
- B32B 37/14: characterised by the properties of the layers
- F24S 70/20: characterised by absorbing coatings; characterised by surface treatment for increasing absorption
- B32B 2255/26: Polymeric coating
- B32B 2264/108: Carbon, e.g. graphite particles
- B32B 2266/0257: Polyamide
- B32B 2266/122: Hydrogel, i.e. a gel containing an aqueous composition
- B32B 2305/026: Porous
- B32B 2307/30: having particular thermal properties
- B32B 2307/412: Transparent
- C08J 3/075: Macromolecular gels
- C08J 2333/26: Homopolymers or copolymers of acrylamide or methacrylamide
- B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- F28F: DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION (water and air traps, air venting F16)
- F24S: SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS (for producing mechanical power from solar energy F03G6/00)
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)

## Abstract

A passive thermal management system and methods of using a thermoresponsive hydrogel coating configured to autonomously switch between a heating state and a cooling state based on ambient temperature. At temperature greater than a lower critical solution temperature of the thermoresponsive hydrogel, the thermoresponsive hydrogel coating becomes solar reflective and has enhanced radiative cooling ability to achieve daytime radiative cooling. At temperatures less than the lower critical solution temperature, the thermoresponsive hydrogel coating becomes transparent to facilitate absorption of solar radiation by sun absorber.

## Claims

### Claim 1

A passive thermal management system, comprising:
a substrate; and
a thermally responsive multilayer structure on the substrate, the thermally responsive multilayer structure including:
an inner porous layer on the substrate, wherein the inner porous layer serves as a water reservoir, and
an outer composite layer on the inner porous layer, the outer composite layer being composed of a thermally switchable sublayer and an optically absorptive sublayer, the thermally switchable sublayer configured to autonomously transition between a heating absorbing state and a heat dissipation state in response to a change in ambient temperature, the optically absorptive sublayer configured to absorb solar radiation; and
one or more encapsulating layers on the multilayer structure, wherein the at least one encapsulating layer is composed of an optically transparent material;
wherein the thermally switchable sublayer comprises a thermally responsive polymer hydrogel, and wherein the optically absorptive sublayer comprises a carbon-based material;
wherein at a temperature less than a lower critical solution temperature of the thermally switchable sublayer, the thermally switchable sublayer absorbs water from the water reservoir, and
wherein at a temperature greater than the lower critical solution temperature of the thermally switchable sublayer, the thermally switchable sublayer releases water to be absorbed by the water reservoir.

### Claim 2 (depends on 1)

The passive thermal management system of claim 1, wherein:
the thermally responsive polymer hydrogel comprises a thermochromic Poly(N-isopropylacrylamide (PNIPAM) hydrogel, and
the carbon-based material comprises graphite.

### Claim 3

A passive thermal management system, comprising:
a substrate; and
a thermally responsive multilayer structure on the substrate, the thermally responsive multilayer structure including:
an inner porous layer on the substrate, wherein the inner porous layer serves as a water reservoir;
an outer composite layer on the inner porous layer, the outer composite layer being composed of a thermally switchable sublayer and an optically absorptive sublayer; and
an encapsulating layer comprising an optically transparent material formed on the multilayer structure;
wherein the thermally switchable sublayer comprises means for autonomously transitioning between a heating absorbing state and a heat dissipation state in response to a change in ambient temperature;
wherein the optically absorptive sublayer comprises means for absorbing solar radiation;
wherein at a temperature less than a lower critical solution temperature of the thermally switchable sublayer, the thermally switchable sublayer absorbs water from the water reservoir, and
wherein at a temperature greater than the lower critical solution temperature of the thermally switchable sublayer, the thermally switchable sublayer releases water to be absorbed by the water reservoir.