Nanoparticle Structure and Dynamics in Bulk and at Interfaces
Core-shell nanoparticles at liquid interfaces
Nanoparticles adsorbed at liquid interfaces can be used as building blocks for the fabrication of functional 2D materials, e.g. composite membranes. Conventional use of metal or oxide NPs stabilized by short, rigid hydrophobic ligands often leads to aggregation and thus poor control on the separation and microstructure at the liquid interface, with consequences on the material properties. These obstacles can be overcome by using particles stabilized by thick, soft polymer brushes; the solvated polymer shells provide stability against aggregation as well as additional control on the inter-particle separation by tuning the polymer molecular weight and architecture. Using responsive, cross-linkable polymers also offers the possibility to fabricate 2D responsive systems.
On route to the realization of such 2D composite membranes we have started by investigating the basic properties of the adsorption and self-assembly of core-shell iron oxide/PEG nanoparticles at water/n-decane interfaces. Such particles can be synthesized and functionalized such that the core size, shell thickness and architecture can be independently and accurately tuned. We have investigated their adsorption by a combination of in situ experiments (dynamic interfacial tension measurements, high energy X-ray reflectivity, particle tracking), numerical simulations and theoretical modeling. This exhaustive characterization has highlighted that particle adsorption is irreversible and strongly depends on the nature of the polymer shell. Moreover, collective effects play a key role in the adsorption kinetics and we found that the polymer shells are highly deformed and stretched at the interface, with direct consequences on the assembly microstructure.
We have also extended these initial studies to investigate the microstructure of interfaces populated by core-shell nanoparticles as a function of their architecture, i.e. core-to-shell size ratios, shell thickness and the effect of a rigid vs. deformable core.
In addition to structural and kinetic adsoprtion studies we have also been investigating the dynamics of this type on nanoparticles in bulk and at interfaces. More results on this topic coming soon!