(185h) Electric-Field Induced Assembly of Anisotropic Polymeric Particles

Physical interactions can be exploited to assemble polymeric particles into complex structures with exotic properties. Here we report our work on the directed-assembly of polymeric particles with anisotropic interactions induced by AC electric fields. The key interactions such as the double layer, dipolar, dielectrophoretic, and electrohydrodynamic interactions can all be controlled precisely by tuning experimental parameters which include salt concentrations, frequency, and field strength. Moreover, both shape and surface functionality on those particles can also be modulated, which significantly affect the particle interactions too.

            In the first example, we report the formation of well defined zig-zag oligomers from polymeric spheres. Those oligomers can also connect and form two-dimensional hierarchical structures. Such an unique assembly can be attributed to the competition and balance among dipolar, dielectrophoretic, and double layer interactions between spheres at different planes. In the second example, we will talk about the assembly of polymeric dimers. By systematically changing the size ratios between two lobes in the dimer, we find the colloidal interactions are strongly dependent on the relative orientation between neighboring dimers. At low frequencies, one standing dimer associate with several lying dimers to form a family of clusters with right- and left-handedness. Interestingly, the broken symmetry also induces an unbalanced electrohydrodynamic flow surrounding the chiral particles and causes them to rotate in opposite directions according to their handedness. At high frequencies, the strong electrostatic and electrohydrodynamic attraction between oppositely oriented dimers induces the formation of one- and two-dimensional structures that closely resemble the Ising lattices. By combing the anisotropy in both particle property and field-induced interactions, we demonstrate that the assembled structures of polymeric particles can be significantly enriched.