Reversible formation of gold nanoparticle–surfactant composite assemblies for the preparation of concentrated colloidal solutions

Abstract

We have developed a simple method for the preparation of nearly mono-dispersed stable gold colloids with a fairly high concentration using a two step procedure. First we synthesize citrate capped gold nanoparticles and then exchange the citrate ions with triethyleneglycolmono-11-mercaptoundecylether (EGMUDE). This leads to the immediate precipitation and formation of composite assemblies. The gold nanoparticles were successfully self-redispersed after a few days. The prepared gold colloid can be easily concentrated up to 20 times by separation of the flocculated part. UV-visible spectra, transmission electron microscopy (TEM), and dynamic light scattering (DLS) were used to characterize the products thus formed.

Optical properties of a fabricated self-assembled bottom-up bulk metamaterial

“…At the beginning the diameter of the supramolecular clusters amounts to about 1 µm (for 17 nm gold NPs) and becomes smaller in the following time which has been proven by dynamic light scattering in Ref. [21]. In the third stage (approximately 24 h after EGMUDE addition for 17 nm gold NPs) the supramolecular clusters dissolve (no explicit outer shape can be observed) and clearly ordered phases are observed as can be seen in Fig.…”

“…There the distance between the particles corresponds to twice the length of the EGMUDE molecule as it was mentioned in Ref. [21], in other words all NPs should be fully covered by EGMUDE at this stage. It has to be stressed that the supramolecular clusters, whose optical properties are in the focus of interest in this contribution, are only temporarily stable since they dissolve themselves in the third stage.…”

“…Depending on the time, a self-assembly process is initiated that consists of three distinct stages [21].…”

“…This section is kept rather concise since more details can be found elsewhere [21]. Then we proceed in theoretically investigating the fabricated structures.…”

Self-assembled plasmonic metamaterials

“…chapter 3) that spherical arrangements of plasmonic NPs are of significant interest to the MMs community due to the possibility of introducing magnetic resonances, a necessary building block of negative refractive index materials [ 112 , 113 ]. By replacing the citrate capping shell that stabilizes gold NPs fabricated using the Turkevich method with 11-mercaptoundecylether it is possible to provoke the self-organization of the particles into spherical clusters of around 1 μ m in diameter [ 56 ]. These nanospheres, in turn, were also observed to assemble into larger structures, forming hierarchical arrangements of plasmonic NPs that closely resemble structures that have been proposed as possible negative permeability materials [ 112 ].…”