Start-up of electrophoresis of an arbitrarily oriented dielectric cylinder.

An analytical study is presented for the transient electrophoretic response of a circular cylindrical particle to the step application of an electric field. The electric double layer adjacent to the particle surface is thin but finite compared with the radius of the particle. The time-evolving electroosmotic velocity at the outer boundary of the double layer is utilized as a slip condition so that the transient momentum conservation equation for the bulk fluid flow is solved. Explicit formulas for the unsteady electrophoretic velocity of the particle are obtained for both axially and transversely applied electric fields, and can be linearly superimposed for an arbitrarily-oriented applied field. If the cylindrical particle is neutrally buoyant in the suspending fluid, the transient electrophoretic velocity is independent of the orientation of the particle relative to the applied electric field and will be in the direction of the applied field. If the particle is different in density from the fluid, then the direction of electrophoresis will not coincide with that of the applied field until the steady state is attained. The growth of the electrophoretic mobility with the elapsed time for a cylindrical particle is substantially slower than for a spherical particle.

Enhancement of polymer luminescence by excitation-energy transfer from multi-walled carbon nanotubes.

Carbon nanotubes have been shown to efficiently quench luminescence from conjugated polymers when incorporated in a composite. However, shown here is an up to 100-fold increase in the visible photoluminescence signal from fluorescent chromophores in nylon 10,10 by incorporating multi-walled carbon nanotubes (MWCNTs). Using 325- and 488-nm excitation the optical absorption by MWCNTs embedded within the polymer matrix is demonstrated, followed by efficient excitation-energy transfer to emissive chromophores intrinsic to the polymer but only when the MWCNTs are acid functionalized. Furthermore, the MWCNTs are shown to significantly retard photobleaching of fluorescent centers in the nylon composites. These remarkable properties greatly advance the prospects of utilizing MWCNTs in organic solar cells and electroluminecent devices to improve performance.