When deformed beyond their elastic limits, crystalline solids flow plastically via particle rearrangements localized around structural defects. Disordered solids also flow, but without obvious structural defects. We link structure to plasticity in disordered solids via a microscopic structural quantity, “softness,” designed by machine learning to be maximally predictive of rearrangements. Experimental results and computations enabled us to measure the spatial correlations and strain response of softness, as well as two measures of plasticity: the size of rearrangements and the yield strain. All four quantities maintained remarkable commonality in their values for disordered packings of objects ranging from atoms to grains, spanning seven orders of magnitude in diameter and 13 orders of magnitude in elastic modulus. These commonalities link the spatial correlations and strain response of softness to rearrangement size and yield strain, respectively.

Polymer nanocomposite films (PNCFs) with extremely high concentrations of nanoparticles are important components in energy storage and conversion devices and also find use as protective coatings in various applications. PNCFs with high loadings of nanoparticles, however, are difficult to prepare because of the poor processability of polymer-nanoparticle mixtures with high concentrations of nanoparticles even at an elevated temperature. This problem is exacerbated when anisotropic nanoparticles are the desired filler materials. Here we report a straightforward method for generating PNCFs with extremely high loadings of nanoparticles. Our method is based on what we call capillary rise infiltration (CaRI) of polymer into a dense packing of nanoparticles. CaRI consists of two simple steps: (1) the preparation of a two-layer film, consisting of a porous layer of nanoparticles and a layer of polymer and (2) annealing of the bilayer structure above the temperature that imparts mobility to the polymer (e.g., glass transition of the polymer). The second step leads to polymer infiltration into the interstices of the nanoparticle layer, reminiscent of the capillary rise of simple fluid into a narrow capillary or a packing of granules. We use in situ spectroscopic ellipsometry and a three-layer Cauchy model to follow the capillary rise of polystyrene into the random network of nanoparticles. The infiltration of polystyrene into a densely packed TiO2 nanoparticle layer is shown to follow the classical Lucas-Washburn type of behaviour. We also demonstrate that PNCFs with densely packed anisotropic TiO2 nanoparticles can be readily generated by spin coating anisotropic TiO2 nanoparticles atop a polystyrene film and subsequently thermally annealing the bilayer film. We show that CaRI leads to PNCFs with modulus, hardness and scratch resistance that are far superior to the properties of films of the component materials. In addition, CaRI fills in cracks that may exist in the nanoparticle layer, leading to the healing of nanoparticle films and the formation of defect-free PNCFs. We believe this approach is widely applicable for the preparation of PNCFs with extremely high loading of nanoparticles and potentially provides a unique approach to study capillarity-induced transport of polymers under extreme confinement.

In this work, we present the fabrication of nanoporous polymer-infiltrated nanoparticle films (PINFs) with either uniform or graded porosity based on undersaturated capillary rise infiltration (UCaRI) and study the processing-structure-property relationship of these nanoporous PINFs. The UCaRI process involves first generating a bilayer film of a randomly packed nanoparticle layer atop a polymer layer, such that the volume of the polymer is less than the void volume in the nanoparticle packing. Subsequently, the bilayer film is annealed above the glass transition temperature of the polymer to induce polymer infiltration into the voids of the nanoparticle packing. Using in situ spectroscopic ellipsometry and molecular dynamics simulations, we observe that the polymer transport occurs in two stages: capillarity-induced infiltration, followed by gradual spreading, likely via surface diffusion. By varying the annealing time, UCaRI enables the generation of graded or uniform nanoporous PINFs. We also show that these nanoporous PINFs have tunable optical and mechanical properties, which can be tailored simply by changing the nanoparticle to polymer layer thickness ratio in the initial bilayer. The UCaRI approach is versatile and widely applicable to various polymers, which allows generation of nanoporous PINFs for multiple applications.

Properties of polymers in polymer nanocomposites and nanopores have been shown to deviate from their respective bulk properties due to physical confinement as well as polymer-particle interfacial interactions. However, separating the confinement effects from the interfacial effects under extreme nanoconfinement is experimentally challenging. Capillary rise infiltration enables polymer infiltration into nanoparticle (NP) packings, thereby confining polymers within extremely small pores and dramatically increasing the interfacial area, providing a good system to systematically distinguish the role of each effect on polymer properties. In this study, we investigate the effect of spatial confinement on the glass transition temperature ( T) of polystyrene (PS) infiltrated into SiO NP films. The degree of confinement is tuned by varying the molecular weight of polymers, the size of NPs (diameters between 11 and 100 nm, producing 3-30 nm average pore sizes), and the fill-fraction of PS in the NP films. We show that in these dense NP packings the T of confined PS, which interacts weakly with SiO NPs, significantly increases with decreasing pore size such that for the two molecular weights of PS studied the T increases by up to 50 K in 11 nm NP packings, while T is close to the bulk T in 100 nm NP packings. Interestingly, as the fill-fraction of PS is decreased, resulting in the accumulation of the polymer in the contacts between nanoparticles, hence an increased specific interfacial area, the T further increases relative to the fully filled films by another 5-8 K, indicating the strong role of geometrical confinement as opposed to the interfacial effects on the measured T values.

We explore the effect of confinement and polymer-nanoparticle interactions on the viscosity of unentangled polymers undergoing capillary rise infiltration (CaRI) in dense packings of nanoparticles. In CaRI, a polymer is thermally induced to wick into the dense packings of nanoparticles, leading to the formation of polymer-infiltrated nanoparticle films, a new class of thin film nanocomposites with extremely high concentrations of nanoparticles. To understand the effect of this extreme nanoconfinement, as well as polymer-nanoparticle interactions on the polymer viscosity in CaRI films, we use two polymers that are known to have very different interactions with SiO2 nanoparticles. Using in situ spectroscopic ellipsometry, we monitor the polymer infiltration process, from which we infer the polymer viscosity based on the Lucas-Washburn model. Our results suggest that physical confinement increases the viscosity by approximately two orders of magnitude. Furthermore, confinement also increases the glass transition temperature of both polymers. Thus, under extreme nanoconfinement, the physical confinement has a more significant impact than the polymer-nanoparticle interactions on the viscosity of unentangled polymers, measured through infiltration dynamics, as well as the glass transition temperature. These findings will provide fundamental frameworks for designing processes to enable the fabrication of CaRI nanocomposite films with a wide range of nanoparticles and polymers.