FIELD-INDUCED SMECTIC ORDERING IN MODEL MAGNETIC INKS

We have performed Brownian dynamics simulations of model colloids of a cicular (cigar-shaped) magnetic particles with aspect ratio 6.5, simil ar to Toda F ceramic-coated metal particles. In the absence of a magne tic held, these have a gel-like structure. We have investigated the ef fect of a magnetic field on this structure. At very low volume fractio ns the particles (after orienting along the field) form chains in the field direction. At more realistic volume fractions (3%-9%), we find a unique filamentary structure, in which the filaments themselves are s mectically ordered. That is, the particles are stacked side-by-side wi th their poles in a common plane. The net effect of the orienting fiel d is to promote aggregation into filaments. (C) 1997 American Institut e of Physics.