Induced gold nanoparticle adsorption to oil/water interfaces

Abstract

The formation of AuNP monolayers and the self-assembly of functionalized AuNPs are important fields of study in multiple disciplines. Using thermodynamic models for the prediction of whether adsorption will occur is a potential path to identifying favourable systems quickly; however, these models require testing to determine whether they have applicability beyond the scope of the study for which they were created. A thermodynamic model is identified and used to screen oils for use in PEGylated-AuNP adsorption experiments. 1-Butanol was selected as the best candidate because of its good modelling results and positive initial performance, attributed to its low interfacial tension with water. Carboxylic acid-functionalized PEGylated AuNPs with 5 nm and 13 nm core sizes were synthesized and tested with different concentrations of NaCl at different pHs to determine where adsorption to the interface was possible. AuNP films from systems comprised of NaCl concentrations of 0.1 M and 0.5 M at pH values of 4 and 8 were selected for study using atomic force microscopy. The results showed that the pH 8 systems at both NaCl concentrations formed monolayers at the interface. To determine whether the packing density of these monolayers could be manipulated, compression using a Langmuir-Blodgett balance was performed, which indicated Gibbs monolayers were being formed and the packing density could not be manipulated through compression.