A novel dielectrophoresis potential spectroscopy for colloidal nanoparticles

Abstract

Dielectrophoresis (DEP) has been widely used to manipulate nanoparticles in microfluidic applications. However, determination of the DEP force of nanoparticles by theoretical models is not easy due to complications caused by the polarization of electrical double layer. Additionally, there is a lack of suitable experimental techniques to quantify the DEP force of nanoparticles. This article reports a statistical mechanics-based experimental method to determine the DEP potential energy of a single particle by measuring the equilibrium number density of particles in a DEP force field. Results show that at high frequencies, the measured potentials agree with the Maxwell-Wagner-O'Konski (MWO) theory. At frequencies lower than the crossover frequency (ω ), the measured potential values are larger than MWO theory's predictions. When an effective particle radius (particle radius plus Debye length) is used to replace the particle radius, MWO theory fits better with the measured potentials on both sides of ω . Also, the measured ω was found inversely proportional to the effective particle radius, which agrees with MWO theory. The new DEP potential spectroscopy is not limited to the size or shape of particles, opening doors to investigate the DEP response functions of quantum dots and proteins in an alternating current electric field.

Nondestructive Characterization of Drying Processes of Colloidal Droplets and Latex Coats Using Optical Coherence Tomography

“…Further, the "coffee ring" flows drive the particles from the center to the edge, resulting in a final "coffee ring" deposition pattern, an uneven coating surface [32,48,49]. In the vertical direction, particles aggregate on the top surface, forming a "skin layer" that inhibits the drying process [33,[50][51][52][53][54]. Furthermore, if the glasstransition temperature (T g ) of particles is above room temperature, particles are stiff, and cracks would be seen in the latex [54][55][56][57][58].…”

“…In the vertical direction, particles aggregate on the top surface, forming a "skin layer" that inhibits the drying process [33,[50][51][52][53][54]. Furthermore, if the glasstransition temperature (T g ) of particles is above room temperature, particles are stiff, and cracks would be seen in the latex [54][55][56][57][58]. To create uniform evaporation, it is important to understand and characterize the drying latex with different T g , particle size and surfactant concentrations.…”

“…Using OCT to characterize the drying process of the waterborne latex droplets has been an active research effort, with an emphasis on observing drying inhomogeneity. In recent studies by Huang et al [54,59], the waterborne latex droplets contained polystyrene particles with different sizes, initial solid contents, and surfactant solid contents (L latex: particle size, ~125 nm; initial solid content, 40.11 wt%; surfactant solid content, 0.2 wt%. S latex: particle size, ~53 nm; initial solid content, 33.43 wt%; surfactant solid content, 1.4 wt%).…”

“…The outer layer had lower scattering intensity, and inner layer had higher scattering intensity. OCT speckle contrast analysis [30,54] was further carried out on the same data. In the outer layer, the higher speckle contrast indicated that motions of particles in these regions were restricted.…”

Gain scheduling PID control for directed self‐assembly of colloidal particles in microfluidic devices

“…The associated control strategies have been based on binary switching between operating conditions 21,24 or on the assumption that the directed self-assembly system behaves linearly, 23 which leads to constant controller parameters. Closed-loop systems of directed self-assembly of colloidal particles are generally speaking nonlinear (e.g., dielectrophoretic forces acting on particles depend in a nonlinear way on the electric-field properties 21,25,26 ), thus controllers with constant tuning parameters may exhibit satisfactory performance only for a limited range of operating conditions. Model-based controllers are well capable to deal with nonlinearities.…”