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Center for Nonlinear Studies |
The active manipulation of superparamagnetic colloids represents the basis for advanced microscale technologies, such as design of micro-robots and pumps, development of tunable materials, experimental modeling of molecular structure dynamics, and measurements with micro-rheological probes. However, the full realization of this application potential requires a better understanding of the magnetization of such colloids in time-varying magnetic fields. Superparamagnetic colloids are structures composed of single-domain ferro-magnetic nano-particles embedded in a solid non-magnetizable micron-sized polymer matrix. Although the individual magnetic dynamics of the individual nano-particles are fairly understood, their interactions might give rise to much more complex behaviors. For instance, a collective magnetic relaxation mechanism with characteristic times orders of magnitude longer than the individual entities. In this context, we measured the magnetic relaxation time of superparamagnetic colloids by analyzing the effective potential between colloids subjected to rotating magnetic fields. Notably, we found that the relaxation time of such particles is in the same order as the time associated with time-varying fields used for typical applications. As a consequence, rotational dynamics and dissolution effects of clusters of particles might be observed in such systems.
Host: Christiano Nisoli (T-4)