Orientation of a dielectric rod near a planar electrode.

We present experimental and theoretical results on suspensions of silica rods in DMSO-water, subjected to an applied electric field. The experimental results indicate that, if the electrode used for generating the electric field is in direct contact with the suspension, a fraction of the rods close to the electrode surface does not stand parallel to the field but instead lies flat on the electrode when the field is switched on. To explain these results theoretically, we modify the coupled dipole method to include "image dipoles", and find that a rod close to the electrode experiences not only the expected global potential energy minimum at an orientation parallel to the electric field, but also a local minimum several times the thermal energy in depth for orientations parallel to the electrode surface.

Can nonadditive dispersion forces explain chain formation of nanoparticles?

We study to what extent dielectric nanoparticles prefer to self-assemble into linear chains or into more compact structures. To calculate the Van der Waals (VdW) attraction between the clusters we use the Coupled Dipole Method (CDM), which treats each atom in the nanoparticle as an inducible oscillating point dipole. The VdW attraction then results from the full many-body interactions between the dipoles.

Communication: Bulkiness versus anisotropy: the optimal shape of polarizable Brownian nanoparticles for alignment in electric fields.

Self-assembly and alignment of anisotropic colloidal particles are important processes that can be influenced by external electric fields. However, dielectric nanoparticles are generally hard to align this way because of their small size and low polarizability. In this work, we employ the coupled dipole method to show that the minimum size parameter for which a particle may be aligned using an external electric field depends on the dimension ratio that defines the exact shape of the particle.

Polarizability and alignment of dielectric nanoparticles in an external electric field: bowls, dumbbells, and cuboids.

We employ the coupled dipole method to calculate the polarizability tensor of various anisotropic dielectric clusters of polarizable atoms, such as cuboid-, bowl-, and dumbbell-shaped nanoparticles. Starting from a Hamiltonian of a many-atom system, we investigate how this tensor depends on the size and shape of the cluster. We use the polarizability tensor to calculate the energy difference associated with turning a nanocluster from its least to its most favorable orientation in a homogeneous static electric field, and we determine the cluster dimension for which this energy difference exceeds the thermal energy such that particle alignment by the field is possible.