Rheology of silver nanocluster solutions under confinement

Drainage of solutions of silver (Ag) nano-clusters, pressed between the two apexes of a double-concaved drop situated in a capillary holder, was studied. The size of clusters was below 2 nm. The aqueous nano-suspension of Ag nano-clusters was stabilized by poly(methacrylic acid) (PMAA). The two tips of the double-concaved drop were pressed by a capillary pressure thus forming a foam nanofilm, the drainage kinetics of which was monitored by interferometry. For comparison, the drainage of foam films containing PMAA aqueous solutions with and without AgNO3 was monitored as well. It was found that steric repulsion occurred between the two film surfaces due to the polymeric chains of PMAA. In addition, we observed also a significant change of this steric repulsion in nano-cluster suspensions, which is explained by changes of the polymer network in the film, affecting the entire drainage and stability of the suspension.