Polymeric Foams with Nanoscopic Cellular Structures Facilitated by UiO-66-X as High-Efficiency Nucleators

Nanocellular polymer foams are highly valued for their light weight, high strength, and unique nanostructures, offering significant potential for diverse applications. However, their fabrication and practical use are constrained by the low cell nucleation efficiency and the necessity for extremely high-pressure foaming processes. In this work, we successfully fabricated polymethyl methacrylate (PMMA) nanocellular foam featuring a cell density on the order of 10¹³ cells cm^-3 at a relatively low foaming pressure of 6.0 MPa. This accomplishment was achieved through the use of UiO-66-X nanoparticles as nucleation facilitators, which exhibited a high nucleation efficiency of 1.94. Four distinct UiO-66-X nanoparticles, each adorned with different functional groups, were synthesized and proven to act as efficacious nucleators for PMMA nanofoams. The successful synthesis of UiO-66-X nanoparticles and the integration of functional groups were corroborated through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The cell dimensions and density of the PMMA nanocellual foam were characterized via SEM analyses. Our findings revealed that the incorporation of UiO-66-X nanoparticles dramatically minimized the cell size of the PMMA foam, thereby attaining an elevated cell density. This enhancement is attributed to a reduction in the free energy for cell nucleation within nanocavities situated at the matrix-nucleator interface. Consequently, the meticulous design of high-performance nucleating particles and the judicious selection of foam matrix constituents emerge as pivotal strategies in the quest for polymer cellular materials exhibiting nanoscale cell dimensions. These insights significantly advance the fabrication of polymer foams with enhanced thermal insulation properties and have broad implications for the realm of honeycomb materials science. By optimizing nucleation mechanisms and material combinations, this work paves the way for the development of advanced cellular polymers tailored for applications where superior insulation or light weight yet robust structures are paramount.