Jamming in Quasi-2D Self-Assembled Nanoparticle Monolayers

In this work, we experimentally probed the interparticle dynamics of iron oxide nanoparticle thin films self-assembled at the liquid-air interface. Upon deposition on a water surface in a Langmuir-Blodgett trough by the drop-casting technique and subsequent lateral compression, iron oxide nanocrystals coated in oleic acid ligands self-assembled into a relatively uniform quasi-2D monolayer. Utilizing X-Ray Photon Correlation Spectroscopy (XPCS) at beamline 8-ID-I of the Advanced Photon Source at Argonne National Lab, we measured the characteristic timescale of in-plane interparticle dynamics. We quantified the aging behavior of the film utilizing both second-order and two-time autocorrelation analysis. We also determined the degree of jamming in the system by a stretched exponential model, yielding exponents varying between a value of 1.5 and 2. We have concluded that despite the quasi-2D nature of our system, verified by x-ray reflectivity, interparticle diffusion in our nanoparticle monolayers bears the signature of a largely three-dimensional jammed system.