Viscoplastic and Granular Behavior in Films of Colloidal Nanocrystals

Abstract

Nanoindentation measurements of electrophoretically deposited films of colloidal CdSe nanocrystals, capped by organic ligands, show the films have an elastic stiffness modulus of approximately 10 GPa and exhibit viscoplasticity. This mechanical response suggests polymeric features that are attributable to the ligands. After particle cross-linking and partial ligand removal, the films exhibit more features of granularity.

Tolerance to structural disorder and tunable mechanical behavior in self-assembled superlattices of polymer-grafted nanocrystals

“…4). The elastic moduli measured here are comparable to the values for nanocrystal arrays containing short, alkyl ligands measured through AFM membrane deflection (7)(8)(9) and nanoindentation (19)(20)(21), and are higher than the modulus of polystyrene-grafted silica nanoparticle films with similar polymer molecular weight and concentrated polymer brushes (24). The Halpin-Tsai model was used to separate the contribution of the polymeric and inorganic components to the superlattice elastic modulus in superlattices prepared at RT-covered (38,47).…”

“…This class of superlattices provides an ideal framework for developing a mechanistic understanding of the novel mechanical properties of nanocrystal superlattices because superlattice structure, dimensions, and ligand length can be varied across a wide range of conditions and the effect of each of these parameters can be independently evaluated. In comparison, previous work showed that the elastic modulus, ductility, and hardness of nanocrystal arrays are influenced by ligand and nanocrystal type, and nanocrystal packing, but the alkyl ligands in these studies differed in length only by a few carboncarbon bonds, and structural variations were not quantified (7,9,(19)(20)(21). Polymer-grafted nanocrystal superlattices also differ from composites made from nanoparticles grafted to polymers with lengths of tens to thousands of monomers, because these composites usually contain aggregates or randomly dispersed nanoparticles instead of precisely ordered, periodic microstructures (22)(23)(24)(25)(26)(27).…”

Nanomechanical Properties of TiO2 Granular Thin Films

“…This forms a highly porous, granular structure, where the mechanical properties are highly influenced by the relatively weak binding between the particles. It has been reported that granular films show compaction behavior of a loosely packed granular material because neighboring grains slide around and past each other, which results in completely different mechanical properties, compared with non-granular films, such as sputtered films or bulk materials (47,72).…”

Mechanical properties of Al2O3 inverse opals by means of nanoindentation

“…This work is aimed to analyze the micromechanical response of alumina inverse opals [4,8]. Although the mechanical response of silica colloidal crystals [5], capped nanocrystals and supercrystals films [6,7,12], and polymer-stabilized or sintered aggregates [13], has been studied by nanoindentation at the nanometric length scale; similar information at the micrometric length scale of Al 2 O 3 inverse opals is not available in the open literature. In this study, nanoindentation techniques are used for reliable micromechanical characterization of Al 2 O 3 inverse opal under different contact stresses, mainly to determine the elastic and elasto-to-plastic properties.…”

“…Although it is possible to fabricate inverse opals by lithographic or ion beam techniques [4], self-assembly process is more flexible and cost effective for production [5,6,7]. Conventional selfassembly technologies have achieved either large area layers or highly ordered layers, but hardly both of them [8].…”