Hydrogels enable negative pressure in water for efficient heat utilization and transfer

TL;DR

This paper introduces a novel hydrogel-based system that generates high negative water pressure, enabling efficient heat transfer and energy conversion, with potential applications in heat pipes and power generation.

Contribution

It presents a new hydrogel structure capable of sustaining large negative pressure and demonstrates its use in heat transfer and energy harvesting devices.

Findings

Achieved a negative pressure of -1.61 MPa using hydrogel films.

Generated 1.06 V voltage from environmental energy via streaming potential.

Realized a high heat transfer density of 11.2 kW/cm² with a 1-meter flow length.

Abstract

Metastable water in negative pressure can provide giant passive driving pressure up to several megapascals for efficient evaporation-driven flow, however, the practical applications with negative pressure are rare due to the challenges of generating and maintaining large negative pressure. In this work, we report a novel structure with thin hydrogel films as evaporation surfaces and robust porous substrates as the supports, and obtain a high negative pressure of -1.61 MPa through water evaporation. Molecular dynamics simulations elucidate the essential role of strong interaction between water molecules and polymer chains in generating the negative pressure. With such a large negative pressure, we demonstrate a streaming potential generator that spontaneously converts environmental energy into electricity and outputs a voltage of 1.06 V. Moreover, we propose a "negative pressure heat pipe" for the first time, which achieves a high heat transfer density of 11.2 kW cm-2 with a flow length of 1 m, showing the potential of negative pressure in efficient heat utilization and transfer.