Neutron scattering techniques for the investigation of nanoparticles surface nanodomains and interfacial properties

Orateur : Mauro MOGLIANETTI (Italian Institute of Technology IIT, Via Barsanti, 1, Arnesano 73010 (LE), Italy)

Naturally occurring surfaces are structured with nanometre-scale domains, yet a framework providing a quantitative understanding of how nanostructures form and affect interfacial properties is lacking. When a mixture of ligand molecules is used to coat metallic nanoparticles, nanodomains occur that impart many structure-depended properties like in proteins and other complex molecules. We performed small angle neutron scattering (SANS) to study the nanodomains characteristics present at the surface of the nanoparticles. This was the first report to compare evidence of the existence of stripe-like domains for particles in solution using SANS together with Scanning Tunneling Microscopy (STM), and we believe that a combination of these two techniques could become a major approach to characterize mixed ligand nanomaterials in solution.1 We also present a method, based on in situ neutron reflectivity (NR), for calculating contact angle from which we derive the adsorption and interfacial energy of nanoparticles at the air-water interface. The average immersion depth of the monolayer is determined by comparing NR curves for monolayers at water subphases of varying neutron contrasts with suitable geometrical models. Contact angles were also calculated via atomistic molecular dynamics (MD) computations and were in agreement with experimental results. We demonstrate that this approach can be used to differentiate between NPs in which the ligands are segregated forming a Janus configuration from NPs where the ligands are uniformly mixed or form small subnanometer domains.2 Our method is general and can be extended to analyze a wide range of nanoparticles at interfaces.

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