Passive thermal management using thermoresponsive hydrogel

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.