Application of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and polyethyleneimine (PEI) in thermal management

Abstract

Throughout the past century, society has experienced profound industrialization, electrification, and informatization, accompanied by an escalating need for effective thermal management. This requirement emerges in a variety of sectors, including industrial processes and electronics, where excessive heat may result in equipment damage, reduced efficiency, and potential safety hazards. Concurrently, low-grade waste heat is a prevalent byproduct of these processes and is also encountered in everyday environments. Targeting efficiency and decreased emissions, polymer materials emerge as promising candidates for thermal management applications including efficient transfer, storage, dissipation and conversion of heat. To enhance heat dissipation on exceptionally hot surfaces, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was selected to counteract the Leidenfrost effect that impedes heat transfer at elevated temperatures. The formation of unique granulated PVDF-HFP matrix involves two pivotal processes: a non-solvent induced phase separation (NIPS) for producing the porous precursor film, and a heating-induced Rayleigh-Bernard convection for the morphological evolution. Hydrodynamic experiments and high-speed imaging demonstrate that the matrix can create non-uniform temperatures, facilitate lateral wicking, augment thermal cooling, and suppress the Leidenfrost effect. Furthermore, due to the inherent thermal oxidation stability and mechanical strength of PVDF-HFP, it is capable of withstanding quenching on different substrates at temperatures exceeding 400 °C. Another application of PVDF-HFP is radiative cooling, a process where an object emits thermal radiation to its surroundings without significantly absorbing environmental heat. Exploiting the hierarchical porous structure induced by NIPS, the micropores and nanopores in PVDF-HFP effectively scatter sunlight, thereby reducing solar thermal absorption. The integration of fluorinated silicon dioxide into the porous PVDF-HFP matrix not only enhances emitting radiation across the atmospheric window but also imparts self-cleaning properties, promising sustained high-performance cooling in demanding environments. The efficacy of this polymer composite is underscored by COMSOL simulations, which show a temperature reduction of nearly 17 °C below ambient levels during a 24-hour period in autumn in Hong Kong. Beyond further advancing the PVDF-HFP with enhanced reflectance for practical radiative cooling applications, we also recognize the potential of polymers in low-grade heat harvesting. Ionic thermoelectrics, a burgeoning field within thermoelectric materials that operate on electrochemical systems. Our exploration of various polymer electrolytes has uncovered a unique mechanism that significantly increases the Seebeck coefficient in ionic thermoelectric devices, activated by the temperature-sensitive behaviors of polymer species at the electrode-electrolyte interface. The as-fabricated aqueous thermocell that comprise polyethyleneimine (PEI) as the solute achieves an exceptionally high Seebeck coefficient of 4.8 mV K-1, which is further validated by theoretical calculations and molecular dynamic simulations. Remarkably, the Seebeck coefficient is believed to be further amplified by integrating a PVDF-HFP constrained framework, synergizing with the thermodiffusion effect. Overall, our research underscores the critical role of polymer materials in advancing thermal management strategies, steering us towards a more efficient and energy-conserving future. This realization emphasizes not only the necessity of innovative approaches in managing heat but also the potential of polymers in fulfilling these needs across various industries and applications.