(383f) Coiling of Semiflexible Paramagnetic Colloidal Chains

When exposed to external time-varying magnetic fields, semiflexible chains composed of superparamagnetic colloids deform into various morphologies. Under a circular rotating magnetic field, these chains exhibit various rotational and deformation dynamics such as rigid rotation, folding, wagging, and coiling. The coiling deformation represents a promising approach to load microscopic cargo for subsequent targeted delivery. During coiling, the ends of the chain spiral by wrapping the chain backbone. Here, we investigate the formation of coils in semiflexible chains using numerical simulations. We demonstrate that the size and shape of the initial coil are controlled by the dimensionless Mason and elastoviscous numbers, which are related to field parameters and chain stiffness. The size of the coil exhibits a nonmonotonic trend with Mason number, from which two distinct regimes are identified. The first is an elasticity-dependent nonlinear regime in which the size of the coil decreases as the field strength increases. The second is an elasticity-independent linear regime in which the coil size increases with field strength. From the time-scales associated to the formation of the coils, we also find two distinct coiling mechanisms that correspond to each size regime. These mechanisms also relate the coiling dynamics to two other types of deformation dynamics reported in previous experimental observations of these chains.