Role of the Electric Field Affected Zone (EFAZ) on the Electrophoretic Deposition of TiO 2 Nanoparticles under Symmetric Low-Frequency AC Electric Fields J. Esmaeilzadeh, S. Ghashghaie, B. Raissi Dehkordi,* and R. Riahifar Materials and Energy Research Center, P.O. Box 14155-4777, Tehran, Iran ABSTRACT: In the present study, electrophoretic deposition (EPD) of TiO 2 nanoparticles under the application of symmetric AC fields was investigated. In the first step, EPD of TiO 2 nanoparticles under a DC field at 50 V resulted in the particles’ deposition on one electrode, consistent with conventional EPD principles. However, no deposits were formed on any of the electrode surfaces for symmetric sinusoidal waves at 1 Hz. In this case, enhancing the electric field strength through the application of higher potentials was considered to extend the electric field affected zone (EFAZ) in front of the electrode, increasing the particles’ opportunity to deposit. A kinetic model was then derived based on the Hamaker approach to calculate the deposited mass under an AC electric field. Although this model was found to be in agreement with experimental results at 1 Hz above 200 V, some deviation was detected at lower voltages. This trend shows that there is a threshold field strength below which EFAZ is not wide enough to let particles deposit under an AC electric field. ■ INTRODUCTION The electrophoretic deposition (EPD) technique with a wide range of novel applications in the processing of ceramic materials has been extensively employed to form coatings from submicrometer- and nanometer-sized particles. Cost-effective- ness, a simple apparatus, and relatively short deposition durations are among the main advantages of EPD. In the EPD process, an electric field is applied between two electrodes, and charged particles suspended in a suitable liquid medium move toward the oppositely charged electrode, creating a relatively compact and homogeneous film. Although the EPD process has been dominantly carried out using uniform DC fields, the idea of employing other forms of electric fields such as pulsed DC and AC asymmetric fields has been taken into consideration. Naim et al. 1 used pulsed DC fields to deposit TiO 2 particles. Their results showed that under this condition, the particles will be deposited according to their size. In another study, Van der Biest et al. 2 used asymmetric alternating electric fields for deposition in aqueous suspensions. They finally showed that for α-alumina particles, the quality of the layer obtained under asymmetric AC fields is better in comparison with layers formed under conventional DC fields. The two formerly mentioned methods also eliminate the water electrolysis reaction in aqueous suspensions, limiting the bubbling within the suspension during deposition. Although the application of pulsed DC and asymmetric AC fields was found to have desirable consequences in the EPD process, there are no major interests in using symmetric fields for deposition. The main belief among research in this case is that the net movement of a particle in one cycle is zero when symmetric waves are applied. Hirata et al. investigated the deposition of alumina particles under symmetric AC fields in aqueous media, where the deposition rate was extremely low, being controlled by the diffusion of alumina in the suspension. On the basis of their findings, they concluded that no net electrophoresis occurs under the influence of symmetric AC fields. 3 In our previous studies, we showed that the application of symmetric waves to coplanar gold electrodes will result in the particles’ deposition on both electrodes as well as the interelectrode gap. 4 Although the assembly of suspended particles under nonuniform AC electric fields is mostly attributed to a polarization effect and dielectrophoresis force, we successfully showed that deposition would take place even at frequencies as low as 0.1-1 Hz, where the electrophoresis force is still dominant. 5 Special Issue: Electrophoretic Deposition Received: June 2, 2012 Revised: September 25, 2012 Published: October 24, 2012 Article pubs.acs.org/JPCB © 2012 American Chemical Society 1660 dx.doi.org/10.1021/jp3054235 | J. Phys. Chem. B 2013, 117, 1660-1663