Self-assembly is universal for any given matter across all scales.

Self-assembly of nanoparticles (NPs) as liquid dispersions has been extensively researched over the last couple decades.   NPs have unique properties which are often vastly different from their macroscale states, with myriad potential applications in electronics, photonics and biology.   However, incorporation of these properties into macroscale functional applications has been limited.   An essential challenge is the integration of such unique properties into assemblies for macroscale devices.  

 

By exploring self-assembly of solid-state nanomaterials we aim to more fully comprehend underlying mechanisms and dynamics in order to devise a wide range of advantageous applications.   Our research relies upon concepts from chemical engineering, materials science, biology and mathematics to assemble macroscale solid-state materials and to analyze their unique properties.   We aspire to uncover multifarious technological holy grails such as stretchable conductors, chiroptical meta-materials and tunable gratings adding values by lowering cost, minimizing preparation time and employing macroscale large area samples.

 

Stretchable Nanoparticle Conductors

We first demonstrated an example of excellent stretchable conductors from self-assembly of NPs.   Free-standing stretchable conductors were prepared by layer-by-layer (LBL) assembly.   High conductivity and stretchability were observed and the properties originated from dynamic self-organization of NPs.   Modified percolation theory to incorporate the self-assembly gave excellent match with experimental data.

 (from left to right)   Photograph of a free-standing Au NP composite.   Calculated conductivity dependence on strain for composites described by percolation theory.   TEM images of NP layers under strain of 0%, 30%, and 50%.

(from left to right)   Photograph of a free-standing Au NP composite.   Calculated conductivity dependence on strain for composites described by percolation theory.   TEM images of NP layers under strain of 0%, 30%, and 50%.

Yoonseob Kim et al., Nature 500, 59–63 (2013)  [download pdf] [supplementary info]

 

Reconfigurable Chiroptical Nanocomposites

The recent study first demonstrated the chiroptical nanocomposites for the applications of metamaterials devices and optoelectronics.   They were LBL assembled from NPs and single-walled carbon nanotubes (SWNT).   Chiroptical activities were reversibly tunable by macroscale stresses.   S-like non-planar nano-assemblies are responsible for the optical activities and this was confirmed by computational simulations.

 (from left to right)   Chiroptical nanocomposites from gold NPs.   Circular dichroism (CD) spectra of the composites under strains of 0, 10, 25 and 50%.     Stimulated emission depletion microscopy images of chiroptically assembled NPs in mirror symmetry.

(from left to right)   Chiroptical nanocomposites from gold NPs.   Circular dichroism (CD) spectra of the composites under strains of 0, 10, 25 and 50%.   Stimulated emission depletion microscopy images of chiroptically assembled NPs in mirror symmetry.

Yoonseob Kim et al., Nature Materials 15, 461–468 (2016)  [download pdf] [supplementary info]