Influence of Bound versus Non-Bound Stabilizing Molecules on the Thermal Stability of Gold Nanoparticles

Abstract

Knowledge concerning the sintering behavior of gold nanoparticles (AuNPs) allows for improved nanomaterials for applications such as printed electronics, catalysis and sensing. In this study, we examined the ability of a range of compounds to stabilize AuNPs against thermal sintering and compared compounds with and without functional groups that anchor the molecules to the nanoparticle surface. Thermal stability was characterized in terms of the temperature of the sintering event (TSE) as well as thermogravimetric analysis and scanning electron microscopy. We show that anchored stabilizing compounds with high thermal stability are effective at preventing the sintering of AuNPs until the decomposition of the compound. A TSE of 390 °C was achieved using 1pyrenebutanethiol as stabilizer. Of the unanchored stabilizers, which were combined with butanethiol-capped AuNPs, two were found to be particularly effective: oleylamine (TSE ≈ 300 °C) and a perylenedicarboximide derivative (TSE ≈ 540 °C), the latter conferring an unprecedented level of thermal stability on ligand-stabilized AuNPs. When selecting stabilizers without anchoring groups, our results demonstrate the importance of choosing those that have an affinity with the capping ligands on the AuNPs to ensure a uniform mixture of AuNPs and stabilizer within a film.

On the Development of Optical Properties during Thermal Coarsening of Gold Nanoparticle Composites

“…The reflectance spectra collected during the heating of a film of BT@AuNPs (Supporting Information, Figure S7) follow a trend very similar to those of OT@AuNPs, but with the sharp increase in reflectance occurring at a lower temperature of 160 °C, as expected for AuNPs stabilized with a shorter alkanethiol. 13,20,33 The alkanethiol-stabilized AuNPs sinter too rapidly for any detailed information on the optical properties and structural changes that occur during the sintering process to be acquired. A system with a more gradual onset of percolation is required if details of the transient properties are desired.…”

“…Py@AuNPs have much greater thermal stability than BT@ AuNPs and OT@AuNPs, with a T SE as high as ∼390 °C. 20 In addition, the sintering event occurs over a significantly wider temperature range, on the order of ∼100 °C. 20 The reflectance data collected while heating a film of Py@AuNPs are shown in Figures 3 and S10 of the Supporting Information.…”

“…20 In addition, the sintering event occurs over a significantly wider temperature range, on the order of ∼100 °C. 20 The reflectance data collected while heating a film of Py@AuNPs are shown in Figures 3 and S10 of the Supporting Information. A plasmon resonance peak was initially observed at ∼600 nm (Figure 3a).…”

“…There was very little change in the spectra from 200 to 250 °C, but between 250 and 335 °C the reflectance of the film significantly decreased across the spectrum (Figure 3b). This decrease is likely due to changes in the optical properties of the PyBuSH stabilizer as it decomposes (which occurs within this temperature range) 20 such as darkening of the color and roughening of the texture, causing less light to be reflected, which was observed during the heating of a related compound, 1pyrenebutanol (PyBuOH, Supporting Information, Figure S11). The NIR reflectance also increased at longer wavelengths between 250 and 335 °C (Figure 3b), suggesting that the gold crossed the percolation threshold to become conductive, which is expected to coincide with the decomposition of the stabilizing compound.…”

“…We have previously shown films of OA@AuNPs to have a relatively high T SE of ∼320 °C. 20 Reflectance at 23 °C (Figure 4a) was low and a plasmon resonance peak was observed at ∼546 nm, with an associated reflectance of 27%. Heating to 100 °C caused a slight decrease in the plasmon peak amplitude, consistent with the literature describing the temperature dependence of the LSPR of AuNPs.…”