(128a) Surface Functionalized Nanoparticles As Surfactants

In this talk, we investigate the interfacial activity of nanoparticles that are surface functionalized by chemically bound, low molecular weight polymers. The specific system that we consider is gold nanoparticles (approximately 3 nm in diameter) with an attached mixture of polybutadiene (PBd) and polydimethylsiloxane (PDMS) to produce a composite particle of approximately 10 nm in diameter. When these particles are introduced into an immiscible PBd-PDMS fluid blend, the particles preferentially adsorb at the interface. We use flow-induced deformation studies for single PBd drops containing a 4 wt% suspension of these nanoparticles to assess the change in interfacial tension due to the adsorption of nanoparticles at the interface. If we allow the drop to equilibrate in the absence of flow, the interfacial tension decreases from 4.6mN/m to 3.0mN/m. However, we find that we can further increase the concentration of particles adsorbed onto the surface (i.e. decrease the interfacial tension) by increasing the surface area via drop deformation and/or drop breakup followed by re-coalescence. In this way, we have further lowered the interfacial tension from 3.0 down to 1.0 mN/m. We also observe that the adsorbed nanoparticles inhibit drop coalescence. But the gold particles we have studied are less effective in this role that an equivalent concentration of copolymer/surfactant. This is due, we believe, to a significant change in the effective Hamaker constant. This illustrates another ?virtue? of nanoparticles as surfactants, however, and that is the fact that they can be used to modify other properties of the blend.