(141b) Multicomponent Multidirectional Assembly of Isotropic Particles By Field-Induced Anisotropic Interactions

Authors: 
Bharti, B., North Carolina State University
Velev, O. D., North Carolina State University
Klapp, S. H. L., Technical University, Berlin
Hall, C. K., North Carolina State University
Kogler, F., Technische Universitaet Berlin

Colloidal particles organize into closed-packed domains when the interparticle interaction exceeds the thermal energy. The spatial arrangement of particles within these domains is governed by the properties of attractive pair potential. External electric and magnetic fields have been widely used to introduce anisotropic interactions between particles and organize them into highly ordered arrays. However, colloidal assemblies formed under the joint synchronized action of electric and magnetic fields have not been characterized. We report a single-step, facile and reversible method for the assembly of multiple 2D bidirectional structures. A dispersion of superparamagnetic microspheres is subjected to orthogonal electric and magnetic fields. The application of external fields induces two distinct dipoles in each particle (one magnetic and one electric). The double dipolar particles interact in aqueous phase and assemble into two dimensionally percolated network. The sequence of electric and magnetic field application determines the equilibrium and non-equilibrium morphology of assembled 2D structure. We find that the particles number density in dispersion governs the network interconnectivity and the rate of formation. In addition to the experiments, we perform Brownian dynamic simulations on the double dipolar particles and find excellent correlation between the two. The combined results of our new experimental approach and the simulation apparatus offers a potential way for the fabrication of smart gels and biresponsive functional materials that can be useful in electronics and biomedical applications.