Conductivity enhancement in carbon nanocone adhesive by electric field induced formation of aligned assemblies.

We show how an alternating electric field can be used to assemble carbon nanocones (CNCs) and align these assemblies into microscopic wires in a commercial two-component adhesive. The wires form continuous pathways that may electrically connect the alignment electrodes, which leads to directional conductivity (∼10(-3) S/m) on a macroscopic scale. This procedure leads to conductivity enhancement of at least 2-3 orders of magnitude in the case where the CNC fraction (∼0.2 vol %) is 1 order of magnitude below the percolation threshold (∼2 vol %). The alignment and conductivity are maintained on curing that joins the alignment electrodes permanently together. If the aligned CNC wires are damaged before curing, they can be realigned by an extended alignment period. This concept has implications in areas such as electronic packaging technology.

Aggregation dynamics of nonmagnetic particles in a ferrofluid.

Nonmagnetic microspheres confined in a ferrofluid layer are denoted by magnetic holes. They form aggregates due to dipolar interactions when an external magnetic field is exerted. Their cluster-cluster aggregation was studied for various magnetic fields using optical microscopy, both for small spheres of diameters, d=1.9 and 4 microm, for which Brownian motion was important and for large spheres of diameter, d=14 microm, for which Brownian motion was not important. The results for the two smaller sizes were in agreement with standard dynamic scaling theory and the dynamic scaling exponent z for the average cluster length S(t) approximately t(z) was found to be slightly smaller than 0.5, while for the largest spheres the z exponent showed a strong dependence on the magnetic-field strength.

Interaction model for magnetic holes in a ferrofluid layer.

Nonmagnetic spheres confined in a ferrofluid layer (magnetic holes) present dipolar interactions when an external magnetic field is exerted. The interaction potential of a microsphere pair is derived analytically, with precise care for the boundary conditions along the glass plates confining the system. Considering external fields consisting of a constant normal component and a high frequency rotating in-plane component, this interaction potential is averaged over time to exhibit the average interparticular forces acting when the imposed frequency exceeds the inverse of the viscous relaxation time of the system. The existence of an equilibrium configuration without contact between the particles is demonstrated for a whole range of exciting fields, and the equilibrium separation distance depending on the structure of the external field is established. The stability of the system under out-of-plane buckling is also studied. The dynamics of such a particle pair is simulated and validated by experiments.