Aggregation of superparamagnetic colloids strongly confined in spherical cavities under magnetic fields

Abstract

Aggregates of superparamagnetic colloids confined in liposomes in the presence of a controllable external magnetic field are studied here by computer simulation. A model of a hard sphere with a central dipole has been used to simulate secondary particles of colloids confined to move within a liposome, which is modelled as a hard spherical cavity. We focus our study on the structure of aggregates created by secondary particles, which in turn are formed by superparamagnetic particles. This study was performed by using the conventional Monte Carlo simulations and the cluster-moving Monte Carlo method. The results obtained with both methods show a dependence on the number of particles and on the ratio cavity-colloid diameters. However, the usual Monte Carlo method does not allow the collective movement of the aggregates. The simulation results show, that for the particular case of the liposome diameter obtained from the experiments ${\sigma }_c=30$, the formation of a single ribbons located at the centre of the cavity for N = 30 and N = 60. In addition, we analyse the structure formation for different values of ${\sigma }_c=N\sigma$, the equilibrium structures are chains for systems for lower ${\sigma }_c^{\ast }<30$, whereas ribbons formation are structures of equilibrium for ${\sigma }_c\gtrsim {\sigma }_c^{\ast }$.

GRAPHICAL ABSTRACT

Keywords:

• Superparamagnetic colloidal particles
• chain formation
• ribbon formation
• magnetoliposomes

Acknowledgments

The authors thankfully acknowledge the computer resources, technical expertise and support provided by the Laboratorio Nacional de Supercómputo del Sureste de México, CONACyT network of national laboratories. We thank Francisco Gámez and M. L. González for fruitful discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Thanks to the CONACyT (National Council of Science and Technology, Mexico) project no. 169504 and CB-256132 that founded the experiments.