Purification–chemical structure–electrical property relationship in gold nanoparticle liquids

Abstract

Macroscopic assemblies of nanoparticles with fluid like characteristics, i.e. nanoparticle liquids (NPLs), are a new class of materials that exhibit unique properties compared with dispersions of nanoparticles in a molecularly distinct matrix phase. By focusing on reaction ratios, techniques to maximize concentration of reactants and quantification of chemical content during washing steps, a high degree of control over the purity of NPLs was maintained while allowing for easy scalability in batch sizes and synthesis throughput. A range of tertiary amines and quaternary ammoniums were used to successfully synthesize Au NPLs from a range of Au nanoparticles with nominal diameters from 6 to 20 nm and initially stabilized with either citrate or dodecanethiol. Stable Au NPLs after purification exhibited a sub-equivalence ratio of canopy to ligand molecules within the corona. This small canopy density most likely arose from the incommensurate areal density of anionic charge within the ligand shell relative to the larger size of the cationic canopy molecule, resulting in a population of cation-anion pairs too weakly bound to be retained in the initial assembly of the canopy post-purification. Finally, increasing either the volume fraction or molecular weight of the canopy was found to increase exponentially the electrical resistance of the bulk NPLs. Removal of excess canopy molecules created a conductive Au NPL that improved hot-current switching durability by at least two orders of magnitude beyond prior reports.

Structure and Dynamics of Polymeric Canopies in Nanoscale Ionic Materials: An Electrical Double Layer Perspective

“…In many NIMs, the nanoparticles have a diameter of a few tens of nanometers and the polymeric canopies are several nanometers thick 2 , 3 , 5 , 15 – 18 . The surface charge density of nanoparticles can reach ~−4 e /nm 2 in many systems 5 .…”

Shape‐directed platinum nanoparticle synthesis: nanoscale design of novel catalysts

“…WCR has become one of the most common catalyst preparation methods due to the vastly controllable synthetic parameters. [51] Early reports of this method go as far back as 1857 [52][53][54][55][56] and can be used in systems of gold, [57][58][59] palladium, [60][61][62] cobalt [63] and silver. [64,65] Some of the earliest reports of Pt shape direction using WCR were reported in 1941 by Rampino and Nord [66] and then later by El-Sayed in 1996, [67] but modifications and variations of these syntheses are still being developed today to design catalyst materials with enhanced properties.…”

“…The control of shape and size during platinum nanoparticle synthesis is an essential part of designing and studying catalyst materials with improved activity and selectivity. Recent studies which characterized catalysts' shapes and exposed surfaces indicate that surface structures can be altered to tune catalytic properties . It was also shown that high index facets on a catalyst surface may exhibit higher activities than lower index facets for certain reactions due to the decreased coordination of step edges and defects, but these sites can also be detrimental to other reactions .…”

Challenges for physical characterization of silver nanoparticles under pristine and environmentally relevant conditions

“…10 AgNPs are commercially available in size ranges from 1 nm to 100 nm and are typically surface modified with capping agents such as citrate, starch or polyvinylpyrrolidone (PVP). Indeed, while physico-chemical characterization of NPs by multiple techniques under relevant conditions has attracted attention in recent literature [15][16][17] and numerous lists suggesting minimum characterization reporting requirements of nanomaterials have been generated, 2 critical knowledge gaps still exist. [11][12][13] Because the agglomeration state of AgNPs can also significantly affect transport and biological activity, 14 one of the current uncertainties with respect to investigating the nanoEHS effects and behavior of AgNPs is the variability in size a Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899-8520, USA.…”