Electrophoretic deposition surface charge

Electrophoretic deposition is used extensively in the automobile industry to form undercoats on car bodies and in many other applications. The successful application of electrophoretic deposition relies on choosing the correct environment, particle size, and system chemistry to achieve coatings of the desired properties. Of critical importance is the ability to determine and control surface charge and the structure of the electrical double layer. 

The seeding can be performed under vacuum [102] or by electrophoretic deposition in aqueous or non-aqueous medium [103]. The latter method has been applied to the rapid synthesis of A-type zeolite membranes. Two strategies can be used for an electrostatic attachment of the seeds to the support either a fine-tuned surface charge by pH control and measurement of the support zeta-potential or the adsorption of positively charged polymers [104], and immersion in a suspension whose pH is such that the seed particles are negatively... 

The rheogram in Fig. 1 suggests two possibilities one is the largest amount of LNA adsorption onto an alumina surface in THF and the least in EtAc for steric stability. The other possibility is that the alumina surface is the most highly charged in THF and the least in EtAc for electrostatic stability. Our electrophoretic deposition experiments yielded alumina particles deposition on the positive electrode, which signifies that the alumina surface in THF was... 

The electrophoretic deposition of alumina in the presence of 5 wt% LNA per alumina yielded a deposit on the negative electrode in toluene and on the positive electrode in THE and EtAc. Although LNA is an acid (Eig. 2) relative to the alumina surface, the basic media THE and EtAc overrode the acidity of 5 wt% LNA, causing the negative charge on the alumina surface. In toluene, on the other hand, LNA reversed the charge on the alumina surface. This could be possible because the surface charge of alumina in toluene was nearly zero, shown by the very small amount of deposit of alumina particles on the positive electrode in the absence of LNA. 

Two different electrodeposition techniques are currently in use electrolytic and electrophoretic. Electrolytic deposition occurs at the surface of the cathode when water is reduced to produce hydrogen gas and hydroxyl ions, which results in an increased pH at the electrode surface [115, 118]. Electrophoretic deposition occurs when charged particles, dispersed or suspended in liquid medium, are attracted to and deposited onto a conductive substrate of opposite charge in the presence of an electric field [112, 113, 119]. 

Electrophoretic deposition is used for depositing thin films firom colloidal dispersion (11). Nanosized particles in a sol can be stabilized by steric or electrostatic means, and they develop a charge on the surface. When an electric field is applied, these charged particles move in response to the field and this motion is called electrophoresis for example, positively charged particles will deposit at the cathode. Nanorod arrays have been synthesized by a combination of sol preparation and electrophoretic deposition. The conditions employed for the growth of nanorod arrays by electrophoretic deposition are summarized in Table 7.1 (11). First, the sol is brought in contact with the template. Then a potential is applied (typically... 

Cabot, B. and Foissy, A. (1998) Reversal of surface charges of mineral powder application to electrophoretic deposition of silica for anticorrosion coatings. J. Mater. Sci. Lett., 33, 3945. 

---