Polymer-infiltrated nanoparticle films (PINFs) are a new class of nanocomposites that offer synergistic properties and functionality derived from unusually high fractions of nanomaterials. Recently, two versatile techniques,capillary rise infiltration (CaRI) and solvent-driven infiltration of polymer (SIP), have been introduced that exploit capillary forces in films of densely packed nanoparticles. In CaRI, a highly loaded PINF is produced by thermally induced wicking of polymer melt into the nanoparticle packing pores. In SIP, exposure of a polymer–nanoparticle bilayer to solvent vapor atmosphere induces capillary condensation of solvent in the pores of nanoparticle packing, leading to infiltration of polymer into the solvent-filled pores. CaRI/SIP PINFs show superior properties compared with polymer nanocomposite films made using traditional methods, including superb mechanical properties, thermal stability, heat transfer, and optical properties. This review discusses fundamental aspects of the infiltration process and highlights potential applications in separations, structural coatings, and polymer upcycling—a process to convert polymer wastes into useful chemicals.
Polymer‐infiltrated nanoparticle films (PINFs) that have high volume fractions (>50 vol%) of nanoparticles (NPs) possess enhanced properties making them ideal for various applications. Capillary rise infiltration (CaRI) of polymer and solvent‐driven infiltration of polymer (SIP) into pre‐assembled NP films have emerged as versatile approaches to fabricate PINFs. Although these methods are ideal for fabricating PINFs with homogenous structure, several applications including separations, and photonic/optical coatings would benefit from a method that enables scalable manufacturing of heterostructured (i.e., films with variation in structural properties such as porosity, composition, refractive indices, etc.) PINFs. In this work, a new technique is developed for fabricating heterostructured PINFs with cavities based on CaRI. A bilayer composed of densely packed inorganic NP layer atop polymer NP layer is thermally annealed above the glass transition temperature of the polymer NP, which induces CaRI of the polymer into the interstices of the inorganic NP layer. Exploiting the difference in the sizes of the two particles, heterostructured double stack PINFs composed of a PINF and a layer with large cavities are produced at a moderate temperature (<200 °C). Using these heterostructured PINFs, Bragg reflectors that can detect the presence of wetting agents in water are fabricated.
High internal phase emulsions (HIPEs) and foams are ubiquitous in our daily lives. They are considered f luid composites with an extremely high-volume fraction of f luid fillers. As all other composite materials do, HIPEs and foams exhibit enhanced properties compared with the simple base fluids without liquid/gas fillers. They can disperse a huge amount of immiscible fluids in other fluids, and fluid fillers remarkably change their physicochemical properties, especially their rheological properties. Their unique structural and compositional features make this material special: A large amount of a dispersed phase is in a very small amount of a continuous phase, and they have an unusual flow behavior as soft glassy materials. Because their fluid nature allows many other materials (e.g., small molecules, polymers, colloids) to be easily dispersed inside, they have a huge potential to be transformed into functional materials that cannot easily be obtained with other hard materials. Here, we summarize the recent progress on HIPEs and foams, particularly in terms of four themes: (1) fabrication techniques, (2) stabilizers and their requirements, (3) flow behavior relating to rheological properties, and (4) porous materials templated from HIPEs and foams. We also discuss future directions and what needs to be done for each theme. Finally, although there have been numerous studies on HIPEs and foams, we present the general outlook for HIPEs and foams to better understand them so that they can be applied to new and unprecedented applications.
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