Like atoms and molecules with directional interactions, anisotropic particles could potentially assemble into a much wider range of crystalline arrays and meso-structures than spherical particles with isotropic interactions. In this paper, the electric-fi eld directed assembly of geometrically anisotropic particles-colloidal dimers is studied. Rich phase behavior and different assembly regimes are found, primarily arising from the broken radial symmetry in particles. The orientations of individual dimers depend on the frequency of the electric fi eld, the ramping direction of frequency, and the salt concentration. The competition and balance between the hydrodynamic, electric, and Brownian torques determine the orientation of individual particles, while the competition between the electrohydrodynamic force and dipolar interaction determines the aggregation of aligned particles at a given experimental condition. The fi eld distribution near the electrode is critical to understand the orientation and assembly behavior of colloidal dimers on a conducting substrate. This study also demonstrates the effectiveness, the reversibility, and potential opportunity of applying electric fi eld to control the orientation and direct the assembly of non-spherical particles. In particular, two dimensional close-packed crystals of perpendicularly aligned dimers are obtained, which shows promise in fabricating 3D photonic crystals based on dimer-like colloids and fi eld-directed display.

The second algorithm of Remez can be used to compute the minimax approximation to a function, ƒ( x ), by a linear combination of functions, { Q i ( x )} n 0 , which form a Chebyshev system. The only restriction on the function to be approximated is that it be continuous on a finite interval [ a , b ]. An Algol 60 procedure is given, which will accomplish the approximation. This implementation of the second algorithm of Remez is quite general in that the continuity of ƒ( x ) is all that is required whereas previous implementations have required differentiability, that the end points of the interval be “critical points,” and that the number of “critical points” be exactly n + 2. Discussion of the method used and of its numerical properties is given as well as some computational examples of the use of the algorithm. The use of orthogonal polynomials (which change at each iteration) as the Chebyshev system is also discussed.

Ning Wu and co‐workers report the assembly of geometrically anisotropic particles–colloidal dimers using external electric fields. Both the orientation and the packing of the non‐spherical particles can be controlled reversibly. This study shows promise towards fabricating 3D photonic crystals based on non‐spherical particles and electricfield‐ actuated displays.

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