Measuring Structure and Dynamics of Nanoparticle Surfactant Assemblies at Liquid-Liquid Interfaces*

While many techniques can assess the packing of nanoparticle (NP, D<50 nm) assemblies, such as GISAXS, AFM, and super resolution spectroscopies, they have drawbacks when obtaining dynamics data, as film damage, imaging time, and fluorescent quenching make reliable measurements difficult. The interfacial assembly of NP surfactants (NPS), oppositely charged carboxylated NPs and aminated surfactants, greatly increase NP binding energies and provide a unique platform to overcome these impediments. We used in-situ GI-XPCS, SAXS, and liquid cell TEM (LTEM) to probe the packing and dynamics of NPS assemblies as a function of areal density. XPCS data show Bragg peak formation and assembly transition from a liquid-like phase to a solid film with much longer in-plane relaxation times as jamming progresses. To augment XPCS results we are developing an LTEM approach to directly observe the spatial and temporal NP rearrangements in real time using a step emulsification flow cell. By controlling the molecular aspects that govern NPS interactions in jammed environments, we have elucidated the kinetics and dynamics of the assemblies.