We describe a successful strategy to substantially enhance cell nucleation efficiency in polymer foams by using designer nanoparticles as nucleating agents. Bare and poly­(dimethylsilane) (PDMS)-grafted raspberry-like silica nanoparticles with diameters ranging from ∼80 nm to ∼200 nm were synthesized and utilized as highly efficient cell nucleators in CO2-blown nanocellular polymethyl methacrylate (PMMA) foams. The successful synthesis of core–shell nanoparticles was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller measurements, and transmission electron microscopy. The cell size and cell density of the obtained PMMA micro- and nanocellular foams were determined by scanning electron microscopy. The results show that increased surface roughness enhances the nucleation efficiency of the designer silica particles. This effect is ascribed to a decreased nucleation free energy for foam cell nucleation in the nanocavities at the melt–nucleator interface. For PDMS grafted raspberry-like silica nanoparticles with diameters of 155 and 200 nm, multiple cell nucleation events were observed. These hybrid particles had nucleation efficiencies of 3.7 and 6.2, respectively. The surprising increase in nucleation efficiency to above unity is ascribed to the significant increase in CO2 absorption and capillary condensation in the corresponding PMMA during saturation. This increase results in the presence of large amounts of the physical blowing agent close to energetically favorable nucleation points. Additionally, it is shown that as a consequence of cell coalescence, the increased number of foam cells is rapidly reduced during the first seconds of foaming. Hence, the design of highly efficient nucleating particles, as well as careful selection of foam matrix materials, seems to be of pivotal importance for obtaining polymer cellular materials with cell dimensions at the nanoscale. These findings contribute to the fabrication of polymer foams with high thermal insulation capacity and have relevance in general to the area of cellular materials.

We describe an in situ facile synthetic approach to prepare carbon quantum dot (CQD) fluorescent markers (FMs) for polyethylene (PE) in the presence of agglomerated silica nanoparticles (SiO2 NPs) under mild reaction conditions. First SiO2 NPs, prepared by the Stöber method, were dispersed in toluene. This dispersion was added to a PE solution in toluene. After heating (either in air or under Ar) a fluorescent mixture was obtained. After drying, PE films were obtained by compression molding, which showed strong blue fluorescence, attributed to CQDs. SiO2 NPs loading values varied between 0.5 and 4 wt %. Subsequent to isolation, the fluorescent CQDs were characterized by TEM, UV–vis, and fluorescence spectroscopy. TEM imaging unveiled a lattice spacing value of 0.21 nm of the isolated fluorescent particles which is typical for (100) graphite plane lattice spacing in CQDs. UV spectroscopy and fluorescence measurements show characteristic absorption and excitation spectra for the aromatic core and oxidized surface defects typically observed for CQDs. The emission maximum for PE/CQD samples increased from 394 to 408 nm when the reaction temperature was decreased from 110 to 90 °C, which is attributed to increasing oxygen content in the reaction mixture upon decreasing the reaction temperature. When the reaction was performed under Ar, the PE/CQD samples emitted in the ultraviolet region (286 nm). Finally, we demonstrated that PE samples marked with CQDs can be easily visually identified upon irradiating with 367 nm light. Thus, the marked PE can be used, for example, as a labeling ingredient in master batches for component identification and in recycling.

Silicon-containing nanoparticles are considered a promising class of materials with exciting physical properties and the potential to revolutionize many emerging application areas. This Chapter introduces the fundamental aspects of silicon-containing nanoparticles and their most common production approaches. In addition, we provide a comprehensive overview of the frontiers of silicon-containing nanoparticle research for the growing fields of printable Silicon-containing electronics, theranostics, nanocellular polymer foaming, and catalysis. We include an introduction to readily applicable particle surface modification strategies as well. Finally, the limitations and challenges for the successful commercialization of silicon-containing nanoparticles in the application fields mentioned are also presented and discussed.

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