Confined Silver Nanoparticles in Ionic Liquid Films

Abstract

This work reports the formation of silver nanoparticles (AgNPs) by sputter deposition in thin films of three different ionic liquids (ILs) with the same anion (bis(trifluoromethylsulfonyl)imide) and cation (imidazolium), but with different alkyl chain lengths and symmetries in the cationic moiety ([C4C1im][NTf2], [C2C2im][NTf2], and [C5C5im][NTf2]). Ionic liquid (IL) films in the form of microdroplets with different thicknesses (200 to 800 monolayers) were obtained through vacuum thermal evaporation onto glass substrates coated with indium tin oxide (ITO). The sputtering process of the Ag onto the ILs when conducted simultaneously with argon plasma promoted the coalescence of the ILs’ droplets and the formation, incorporation, and stabilization of the metallic nanoparticles in the coalesced IL films. The formation/stabilization of the AgNPs in the IL films was confirmed using high-resolution scanning electron microscopy (SEM) and UV-Vis spectroscopy. It was found that the IL films with larger thicknesses (600 and 800 monolayers) were better media for the formation of AgNPs. Among the ILs used, [C5C5im][NTf2] was found to be particularly promising for the stabilization of AgNPs. The use of larger IL droplets as capture media was found to promote a better stabilization of the AgNPs, thereby reducing their tendency to aggregate.

Carbon-Induced Changes in the Morphology and Wetting Behavior of Ionic Liquids on the Mesoscale

“…These interactions contribute to the 2D growth process. Coalesced films have been experimentally observed, for instance, for [C 8 C 1 im]­[OTf] and [C 8 C 1 im]­[NTf 2 ]. ,, On other surfaces, such as soda-lime glass, glass coated with conductive oxides, silver, graphene, nickel, as well as mica surfaces, the formation of droplets has been consistently observed for imidazolium-based ILs. ,,,,,,− , The formation of larger droplets with enhanced wetting ability is further promoted when longer alkyl chain lengths are attached to the IL cation. ,,, …”

“…The influence of cations, anions, and the length of the alkyl chain on film wetting and morphology has been investigated. Additionally, the effects of deposition rate, substrate temperature, and roughness on nucleation, droplet formation, and spreading during the film deposition process have all been addressed. ,,,,− The nucleation and growth mechanisms of IL films fabricated through thermal evaporation are primarily governed by three key factors: the surface diffusion of ion pairs, the availability of a minimum free area to promote nucleation, and the subsequent coalescence processes . These processes are significantly influenced by the affinity of the ion pairs to the substrate surface as the surface diffusion of ion pairs, driven by their search for favorable binding sites, plays a crucial role in the initial stages of film formation.…”

“… 46 , 62 , 63 On other surfaces, such as soda-lime glass, glass coated with conductive oxides, silver, graphene, nickel, as well as mica surfaces, the formation of droplets has been consistently observed for imidazolium-based ILs. 8 , 12 , 48 , 53 , 57 , 58 , 61 − 63 , 67 The formation of larger droplets with enhanced wetting ability is further promoted when longer alkyl chain lengths are attached to the IL cation. 57 , 62 , 63 , 67 …”