(98ae) Kinetics of Colloidal Assembly By Direct Current Electric Fields

We quantify and model the kinetics of the assembly of initially dilute colloidal spheres subjected to a DC electric field in a thin gap between parallel electrodes into crystalline structures, as well as the kinetics of the disassembly of these structures.  We test our model’s predictions with experimental measurements for a system of poly(12-hydroxystearic acid) (PHSA)-stabilized poly(methyl methacrylate) (PMMA) spheres dispersed in a mixture of cyclohexylbromide (CHB) and decalin containing 1 mM tetrabutylammonium chloride (TBAC).  The transient evolution of the volume fraction of colloids in the electrode gap is quantified, under conditions of assembly and disassembly, by confocal laser scanning microscopy (CLSM) imaging. We model the kinetics by adapting a model for sedimentation (Davis and Russel, Phys. Fluids A, 1, 82, 1989) to the DC electric field-assisted assembly and disassembly process.  Parameters in the model are the electrophoretic velocity of the spheres in a DC field (which we characterize by direct measurement), the diffusivity of the spheres, and the volume fraction-dependent osmotic pressure of the suspension.  The model’s predictions agree well with the measured kinetics of the assembly and disassembly when the screened Coulombic interactions between the particles are accounted for.  We also demonstrate that the assembly-disassembly process can be repeated multiple times by controlling the DC field.  The results can inform the design of devices that rely on reversible assembly for potential applications in photonics, optics, and sensing.