Non-equilibrium steady-state colloidal assembly dynamics.

Simulations and experiments are reported for nonequilibrium steady-state assembly of small colloidal crystal clusters in rotating magnetic fields vs frequency and amplitude. High-dimensional trajectories of particle coordinates from image analysis of experiments and from Stokesian Dynamic computer simulations are fit to low-dimensional reaction coordinate based Fokker-Planck and Langevin equations. The coefficients of these equations are effective energy and diffusivity landscapes that capture configuration-dependent energy and friction for nonequilibrium steady-state dynamics.

Direct Measurements of kT-Scale Capsule-Substrate Interactions and Deposition Versus Surfactants and Polymer Additives.

We report a novel approach to directly measure the interactions and deposition behavior of functional capsule delivery systems on glass substrates versus the concentration of an anionic surfactant sodium lauryl ether sulfate (SLES) and a cationic acrylamide-acrylamidopropyltrimonium copolymer (AAC). Analyses of three-dimensional optical microscopy trajectories were used to quantify lateral diffusive dynamics, deposition lifetimes, and potentials of mean force for different solution conditions. In the absence of additives, negatively charged capsule surfaces yield electrostatic repulsion with the negatively charged substrate, which inhibits deposition.

Opto-thermophoretic assembly of colloidal matter.

Colloidal matter exhibits unique collective behaviors beyond what occurs at single-nanoparticle and atomic scales. Treating colloidal particles as building blocks, researchers are exploiting new strategies to rationally organize colloidal particles into complex structures for new functions and devices. Despite tremendous progress in directed assembly and self-assembly, a truly versatile assembly technique without specific functionalization of the colloidal particles remains elusive.

Effective colloidal interactions in rotating magnetic fields.

Non-equilibrium, steady-state effective pair potentials of micron-sized superparamagnetic particles in rotating magnetic fields are obtained vs. field frequency and amplitude. Trajectories of center-to-center distance between particle pairs from Brownian dynamic simulations, which were previously matched to experimental measurements, are analyzed to obtain local drift and diffusion coefficients.

Rotating colloids in rotating magnetic fields: Dipolar relaxation and hydrodynamic coupling.

Video microscopy (VM) experiments and Brownian dynamics (BD) simulations were used to measure and model superparamagnetic colloidal particles in rotating magnetic fields for interaction energies on the order of the thermal energy, kT. Results from experiments and simulations were compared for isolated particle rotation, particle rotation within doublets, doublet rotation, and separation within doublets vs field rotation frequency. Agreement between VM and BD results was obtained at all frequencies and amplitudes only by including exact two-body hydrodynamic interactions and relevant relaxation times of magnetic dipoles.