The Buckling Spectra of Nanoparticle Surfactant Assemblies.

Fine control over the mechanical properties of thin sheets underpins transcytosis, cell shape, and morphogenesis. Applying these principles to artificial, liquid-based systems has led to reconfigurable materials for soft robotics, actuation, and chemical synthesis. However, progress is limited by a lack of synthetic two-dimensional membranes that exhibit tunable mechanical properties over a comparable range to that seen in nature.

Direct observation of nanoparticle-surfactant assembly and jamming at the water-oil interface.

Electrostatic interactions between nanoparticles (NPs) and functionalized ligands lead to the formation of NP surfactants (NPSs) that assemble at the water-oil interface and form jammed structures. To understand the interfacial behavior of NPSs, it is necessary to understand the mechanism by which the NPSs attach to the interface and how this attachment depends on the areal coverage of the interface. Through direct observation with high spatial and temporal resolution, using laser scanning confocal microscopy and in situ atomic force microscopy (AFM), we observe that early-stage attachment of NPs to the interface is diffusion limited and with increasing areal density of the NPSs, further attachment requires cooperative displacement of the previously assembled NPSs both laterally and vertically.

Reconfigurable Printed Liquids.

Liquids lack the spatial order required for advanced functionality. Interfacial assemblies of colloids, however, can be used to shape liquids into complex, 3D objects, simultaneously forming 2D layers with novel magnetic, plasmonic, or structural properties. Fully exploiting all-liquid systems that are structured by their interfaces would create a new class of biomimetic, reconfigurable, and responsive materials.

Crystallization and flow in active patch systems.

Based upon recent experiments in which Janus particles are made into active swimmers by illuminating them with laser light, we explore the effect of applying a light pattern on the sample, thereby creating activity inducing zones or active patches. We simulate a system of interacting Brownian diffusers that become active swimmers when moving inside an active patch and analyze the structure and dynamics of the ensuing stationary state. We find that, in some respects, the effect of spatially inhomogeneous activity is qualitatively similar to a temperature gradient.

Frictional dynamics of stiff monolayers: from nucleation dynamics to thermal sliding.

The inherently nonlinear dynamics of two surfaces as they are driven past each other, a phenomenon known as dry friction, has yet to be fully understood on an atomistic level. New experiments on colloidal monolayers forced over laser-generated substrates now offer the opportunity to investigate friction with single-particle resolution. Here, we use analytical theory and computer simulations to study the effect of thermal fluctuations on the stick-slip mechanism characteristic for the frictional response of a stiff colloidal monolayer on a commensurate substrate.