Towards a programmable microfluidic valve: Formation dynamics of two-dimensional magnetic bead arrays in transient magnetic fields

Abstract

The induction of dipolar coupling has proven to allow for the initiation of self-assembled, reconfigurable particle clusters of superparamagnetic microbeads suspended in a carrier liquid. The adjustment of the interplay between magnetic and hydrodynamic forces opens various possibilities for guiding strategies of these superstructures within microfluidic devices. In this work, the formation dynamics of such particle clusters under the influence of a rotating magnetic field are studied. Different agglomeration regimes are characterized by the dimensionality of the confined objects. The growth dynamics of the obtained agglomerates are analyzed quantitatively in order to deduce the microscopic growth mechanisms. The growth of two-dimensional clusters is governed by the addition of bead chains to previously formed agglomerates. Time scales for the cluster growth are characterized by the chain dissociation rate. Based on the experimental findings, we may conclude to a linear dependence of the chain dissociation rate on the rotation frequency of the applied magnetic field.

Structure and dynamics of self-assembling colloidal monolayers in oscillating magnetic fields

“…Despite these differences, there is still an overall agreement in the trend of the master curve, consistent with t s ∝ Mn/ω. Previously, the clustering rate for magnetic particles in a rotating magnetic field was measured for three different frequencies by Wittbracht et al [28]. The investigators found that the clustering rate increased linearly with frequency which is also consistent with the scaling of Calderon and Melle (Eqn.…”

“…Petousis et al showed there is a maximum length under which a chain is stable for a given Mn which scales as Mn −1/2 [21]. The unstable regime in which chains break apart and form two-dimensional clusters has only recently been explored [27,28,34]. Here, we present the correlation length of two-dimensional clusters L as a function of Mn.…”

“…where ω = 2πf is the angular frequency. We note that this experimental design is different from previous experiments involving monolayers of dipolar particles in rotating electric or magnetic fields [20,23,27,28,30] in the sense that one component of the magnetic field remains steady. This introduces a new degree of freedom, the angle θ through which the magnetic field sweeps, as sketched in Fig.…”

“…In steady or slowly rotating magnetic fields such particles form chains, which align with the magnetic field lines [21][22][23][24][25]. If the field rotates too quickly, viscous drag breaks apart 3he chains [21], and the particles can instead form highly organized crystals [26][27][28]. However, previous experiments have not yet explored the role of hydrodynamic interactions in cluster formation.…”

Controlled evaporative self-assembly of Fe3O4 nanoparticles assisted by an external magnetic field

“…3E). 40 However, due to the conned geometry (i.e., sphere-on-at), there is no formation of ordered 2D sheets and leading to only concentric rings when higher magnetic eld rotation frequency is employed (Fig. When the magnetic eld is rotated at low magnetic eld rotation frequency, the chain structures could also rotate (Fig.…”