Needle based droplet microfluidic synthesis of high thermal conductivity Ferrofluid microcapsules for thermal management

• The core/shell structured OMF-HDDA microcapsules exhibit excellent size uniformity with a coefficient of variation less than 5 %. • The OMF-HDDA microcapsules obtain 1 MPa stiffness in a 300 mT direct current (DC) magnetic field, roughly a thousand-fold enhancement compared to that in the absence of a magnetic field. • The photothermal effect of OMF-HDDA microcapsules was confirmed through their heat generation under alternating magnetic fields. • In comparison to water, the application of OMF-HDDA microcapsules in thermal management of electronic chip demonstrate 36.86 % higher temperature control capacity with thermal conductivity of 1.232 W/m·K at magnetic flux density of 300 mT. Efficient heat dissipation remains a critical challenge in advanced thermal management systems, particularly in high-performance electronics and energy-intensive applications. This study presents a novel thermal regulation microcapsule that integrates the magnetic properties of the core material with the stability and tunability of the shell material, offering significant application potential. Using needle-based double emulsion microfluidics, oil magnetic fluid (OMF) was encapsulated within a hexanediol diacrylate (HDDA) shell, achieving precise structural and size control with an average diameter of 406.87 μm and size variation below 5%. Thermal characterization demonstrated that microcapsule heat dissipation efficiency depends on size, temperature, and magnetic flux density, with a thermal conductivity of 1.232 W/m·K under a 300 mT magnetic field, outperforming conventional materials. Mechanical testing revealed variable stiffness, reaching ∼1 MPa in a 300 mT direct current magnetic field, a thousandfold increase compared to non-magnetic conditions. Furthermore, photothermal effects under an alternating magnetic field confirmed their capacity for energy conversion via heat generation. In electronic chip cooling tests, OMF-HDDA microcapsules achieved a 36.86% enhancement in heat dissipation compared to traditional coolants. These findings highlight the microcapsules' innovative potential as a high-performance, environmentally friendly solution for next-generation thermal management systems.