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Arrested Chain Growth During Magnetic Directed Particle Assembly in Yield Stress Matrix Fluids
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posted on 2012-02-28, 00:00 authored by Jason
P. Rich, Gareth H. McKinley, Patrick S. DoyleThe process of assembling particles into organized functional
structures
is influenced by the rheological properties of the matrix fluid in
which the assembly takes place. Therefore, tuning these properties
represents a viable and as yet unexplored approach for controlling
particle assembly. In this Letter, we examine the effect of the matrix
fluid yield stress on the directed assembly of polarizable particles
into linear chains under a uniform external magnetic field. Using
particle-level simulations with a simple yield stress model, we find
that chain growth follows the same trajectory as in Newtonian matrix
fluids up to a critical time that depends on the balance between the
yield stress and the strength of magnetic interactions between particles;
subsequently, the system undergoes structural arrest. Appropriate
dimensionless groups for characterizing the arresting behavior are
determined and relationships between these groups and the resulting
structural properties are presented. Since field-induced structures
can be indefinitely stabilized by the matrix fluid yield stress and
“frozen” into place as desired, this approach may facilitate
the assembly of more complex and sophisticated structures.