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-nanoparticle
composite films (PNCFs) with high loadings
of nanoparticles (NPs) (>50 vol %) have applications in multiple
areas,
and an understanding of their mechanical properties is essential for
their broader use. The high-volume fraction and small size of the
NPs lead to physical confinement of the polymers that can drastically
change the properties of polymers relative to the bulk. We investigate
the fracture behavior of a class of highly loaded PNCFs prepared by
polymer infiltration into NP packings. These polymer-infiltrated nanoparticle
films (PINFs) have applications as multifunctional coatings and membranes
and provide a platform to understand the behavior of polymers that
are highly confined. Here, the extent of confinement in PINFs is tuned
from 0.1 to 44 and the fracture toughness of PINFs is increased by
up to a factor of 12 by varying the molecular weight of the polymers
over 3 orders of magnitude and using NPs with diameters ranging from
9 to 100 nm. The results show that brittle, low molecular weight (MW)
polymers can significantly toughen NP packings, and this toughening
effect becomes less pronounced with increasing NP size. In contrast,
high MW polymers capable of forming interchain entanglements are more
effective in toughening large NP packings. We propose that confinement
has competing effects of polymer bridging increasing toughness and
chain disentanglement decreasing toughness. These findings provide
insight into the fracture behavior of confined polymers and will guide
the development of mechanically robust PINFs as well as other highly
loaded PNCFs.
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.
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