kT-Scale Colloidal Interactions in High Frequency Inhomogeneous AC Electric Fields. I. Single Particles

Abstract

We report nonintrusive optical microscopy measurements of single micrometer-sized silica and polystyrene colloids in inhomogeneous AC electric fields as a function of field amplitude and frequency. By using a Boltzmann inversion of the time-averaged sampling of single particles within inhomogeneous electric fields, we sensitively measure induced dipole-field interactions on the kT energy scale and fN force scale. Measurements are reported for frequencies when the particle polarizability is greater and less than the medium, as well as the crossover between these conditions when dipole-field interactions vanish. For all cases, the measured interactions are well-described by theoretical potentials by fitting a nondimensional induced dipole-field magnitude. While silica dipole-field magnitudes are well-described by existing electrokinetic models, the polystyrene results suggest an anomalously high surface conductance. Sensitive measurements of dipole-field interactions in this work provide a basis to understand dipole-dipole interactions in particle ensembles in the same measurement geometry in part II.

Colloidal crystal grain boundary formation and motion

“…Our previous characterization of electric field mediated colloidal interactions and assembly has yielded kT -scale potentials2021, feedback control over system size18, and conditions to crystallize N particles19. Based on these findings, we set N = 210 in Fig.…”

“…(1) from trajectories like those in Figs. 1 and 2, we analyzed Brownian Dynamic (BD) simulations that were matched to experiments (by capturing all equilibrium and dynamic properties of the quadrupole experiment on the particle scale192021, see Supplementary Methods). This approach was used because statistics on the particle scale are easily obtained to match experiments and simulations, but BD simulations are better suited to generating large numbers of grain boundary trajectories ( e.g.…”

Size dependent thermodynamics and kinetics in electric field mediated colloidal crystal assembly

“…2,3 Within the broad range of approaches to colloidal assembly, our narrower focus includes methods where interactions can be reversibly tuned on the kT-scale to manipulate near-equilibrium self-assembly processes. Examples of this type of approach include tunable van der Waals, 18,19 depletion, 20,21 DNA, 22,23 Casimir, 24,25 and electric eld [26][27][28][29][30][31] mediated interactions. In our previous studies based on tuning kT-scale interactions, we directly measured potentials using video microscopy methods, which we connected to equilibrium microstructures and particle scale dynamics using a suite of modeling tools.…”

“…In this work, we focus on the assembly of quasi-two dimensional (2D) colloidal crystals within interfacial, quadrupole electrodes, where the experiment has been detailed in previous papers (and the ESI †). 26,[28][29][30][31] We recently demonstrated feedback control over electric eld mediated colloidal assembly, 30,31 but limitations remain for robustly manipulating microstructures in such processes. The main requirement is better dynamic models of crystallization to know how to tune interactions to favorably inuence colloidal assembly trajectories.…”

Directed Assembly of Particles for Additive Manufacturing of Particle-Polymer Composites

“…When a non-uniform electric field is used, particles migrate towards field minima or maxima depending on particle and medium properties [ 72 , 73 , 74 ]. This mechanism, known as dielectrophoresis, affects particles with a force that depends on the gradient of the applied electric field [ 75 ]: where ε m is the medium dielectric constant, V p is the particle volume, and f cm is the Clausius–Mossotti factor.…”