Transmittance tuning by particle chain polarization in electrowetting-driven droplets

Abstract

A tiny droplet containing nano/microparticles commonly handled in digital microfluidic lab-on-a-chip is regarded as a micro-optical component with tunable transmittance at programmable positions for the application of micro-opto-fluidicsystems. Cross-scale electric manipulations of droplets on a millimeter scale as well as suspended particles on a micrometer scale are demonstrated by electrowettingon-dielectric ͑EWOD͒ and particle chain polarization, respectively. By applying electric fields at proper frequency ranges, EWOD and polarization can be selectively achieved in designed and fabricated parallel plate devices. At low frequencies, the applied signal generates EWOD to pump suspension droplets. The evenly dispersed particles reflect and/or absorb the incident light to exhibit a reflective or dark droplet. When sufficiently high frequencies are used on to the nonsegmented parallel electrodes, a uniform electric field is established across the liquid to polarize the dispersed neutral particles. The induced dipole moments attract the particles each other to form particle chains and increase the transmittance of the suspension, demonstrating a transmissive or bright droplet. In addition, the reflectance of the droplet is measured at various frequencies with different amplitudes.

Electrorheological Operation of Low-/High-Permittivity Core/Shell SiO2/Au Nanoparticle Microspheres for Display Media

“…6 An electronic paper based on the electrophoretic motion of suspended light-scattering particles in a dielectric fluid when a voltage is applied has been realized by encapsulating the electrophoretic suspension into individual microcapsules or vessels. 7 Among the developed electronic paper display technologies, particle-based systems exhibit excellent performance by displaying the color of the dyed particles. Building an external electric field inside a particle suspension leads to charge/ion accumulation where the conductivity and permittivity feature discontinuities.…”

“…For polymer microspheres, the stringing behavior occurs optimally under an alternating electric field having a frequency in the range 1−50 kHz. 7 Tuning the frequency of the alternating electric field might potentially lead to the linear stringing of specific microsphere materials to change the display's color in a solution containing a mixture of several kinds of colored microsphere materials. Figure 7a reveals the dependence of the transmittance under an electric field of 50 V upon varying the frequency from 100 to 900 kHz.…”

Electrowetting on dielectric device with crescent electrodes for reliable and low-voltage droplet manipulation

“…The devices were prepared by the following processes. The ITO-coated [26][27][28] glass (Kaiwei electronic devices Limited, Zhuhai, China) plates were rinsed by acetone and deionized (DI) water to remove contaminants before the 120 C dehydration bake. Electrodes were patterned using conventional lithographic techniques.…”

Digital Microfluidics for Manipulation and Analysis of a Single Cell

“…Here we focus more on the electric forces, including DEP and EWOD. The DEP force generated with a non-uniform electric field interacting with polarized, suspended particles [ 65 , 66 , 67 ] has been widely used to manipulate cells [ 39 , 63 , 68 , 69 ]. The DEP force is classified as positive DEP (pDEP) and negative DEP (nDEP) based on the polarizability of the particles or cells and the liquid.…”