Novel Fumed Silica–Based Shape–Stabilized Phase Change Materials with Magnetically Boosted Charging Efficiency and Bi–Functional Thermotherapy Ability

In this work, 1-octadecanol (OD) was combined with fumed silica (F-SiO₂) and Fe₃O₄ nanoparticles to form OD/F-SiO₂/Fe₃O₄ shape-stabilized phase change materials (SSPCMs) with low thermal conductivities (TCs) and magnetically boosted charging efficacy. The SSPCMs were studied with varying OD contents of 50-80% and Fe₃O₄ contents of 5.0-12.5%. F-SiO₂ possessed a suitable porosity to stabilize up to 70% OD without liquid leakage. The 70% OD/F-SiO₂/Fe₃O₄ SSPCM exhibited a high heat storage capacity of 147.6 J/g and excellent durability after 500 accelerated thermal cycles. In comparison to pure OD with a low TC of 0.284 W/(m·K), those of 50-70% OD SSPCMs were further reduced to 0.156-0.193 W/(m·K) owing to the addition of F-SiO₂ and Fe₃O₄ nanoparticles with low TCs. In addition, the SSPCMs possessed superparamagnetism inherited from Fe₃O₄ nanoparticles, enabling boosted magnetothermal conversion and storage ability. Indeed, under a low alternating magnetic field (intensity of 0.056 mT), the prepared 70% OD/F-SiO₂/Fe₃O₄ SSPCM was rapidly heated from ∼34 to 76 °C in 360 s, which was 6.4 and 3.8-fold superior to being heated by a convective oven at 100 and 150 °C, respectively. A thermal pad derived from the 70% OD/F-SiO₂/Fe₃O₄ SSPCM exhibited a bi-functional thermotherapy, simultaneously maintaining heat release within 50-55 °C for 30 min and 40-50 °C for 16 min, which was highly suited for high and mid-level thermotherapy, respectively. These merits endow the OD/F-SiO₂/Fe₃O₄ SSPCMs with a promising potential in practical thermotherapy applications.