Abstract
As the interface between human and machine becomes blurred, hydrogel incorporated electronics and devices have emerged to be a new class of flexible/stretchable electronic and ionic devices due to their extraordinary properties, such as softness, mechanically robustness, and biocompatibility. However, heat dissipation in these devices could be a critical issue and remains unexplored. Here, we report the experimental measurements and equilibrium molecular dynamics simulations of thermal conduction in polyacrylamide (PAAm) hydrogels. The thermal conductivity of PAAm hydrogels can be modulated by both the effective crosslinking density and water content in hydrogels. The effective crosslinking density dependent thermal conductivity in hydrogels varies from 0.33 to 0.51 Wm−1K−1, giving a 54% enhancement. We attribute the crosslinking effect to the competition between the increased conduction pathways and the enhanced phonon scattering effect. Moreover, water content can act as filler in polymers which leads to nearly 40% enhancement in thermal conductivity in PAAm hydrogels with water content vary from 23 to 88 wt %. Furthermore, we find the thermal conductivity of PAAm hydrogel is insensitive to temperature in the range of 25–40 °C. Our study offers fundamental understanding of thermal transport in soft materials and provides design guidance for hydrogel-based devices.
Highlights
Soft hydrogels, such as living tissues and cartilages, are one of the main components of human bodies
Heat dissipation in hydrogel-based electronic devices, as well as soft electronics, remains largely unexplored, which may be arisen from the fact that hydrogels used in above domains usually fulfill simple actions based on environmental sensitivity without much participating of electronic components
We explore the thermal conduction mechanism in hydrogels through equilibrium swelling ratio measurements, scanning electron microscope (SEM) characterization, and equilibrium molecular dynamic (EMD) simulation
Summary
Soft hydrogels, such as living tissues and cartilages, are one of the main components of human bodies. The intrinsic nature of hydrogels in between a solid and a liquid brings broad applications such as tissue engineering [2], cell encapsulation [3], drug delivery [4], and soft actuators [1]. The emerging hydrogel-based applications are focused on soft electronics, soft robotics, and machines [5]. Heat dissipation in hydrogel-based electronic devices, as well as soft electronics, remains largely unexplored, which may be arisen from the fact that hydrogels used in above domains usually fulfill simple actions based on environmental sensitivity without much participating of electronic components.
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