Electrophoretic mobilities of dissolved polyelectrolyte charging agent and suspended non-colloidal titanium during electrophoretic deposition

TL;DR

This study investigates the electrophoretic mobilities of titanium particles and charging agents during electrophoretic deposition, emphasizing the importance of measuring both suspension and solution mobilities to understand the process mechanisms.

Contribution

It introduces a detailed analysis of electrophoretic mobilities for non-colloidal titanium particles and charging agents, clarifying electrokinetic stages in electrophoretic deposition.

Findings

Electrophoretic mobilities of suspension and solution are both critical for interpretation.

Three mechanistic stages of electrokinetics are identified and characterized.

Assessment of mobilities helps distinguish surface saturation, diffuse layer compression, and polymer dominance.

Abstract

Coarse (<=20 micron) titanium particles were deposited on low-carbon steel substrates by cathodic electrophoretic deposition (EPD) with ethanol as suspension medium and poly(diallyldimethylammonium chloride) (PDADMAC) as polymeric charging agent. The preceding data demonstrated that Ti particles of ~1-12 micron size, electrosterically modified by the PDADMAC charging agent, acted effectively as colloidal particles during EPD. Owing to the non-colloidal nature of the particles and the stabilization of the Ti particles by electrosteric forces, the relevance of the zeta potential is questionable, so the more fundamental parameter of electrophoretic mobility was used. A key finding from the present work is the importance of assessing the electrophoretic mobilities of both the suspensions and solutions since the latter, which normally is overlooked, plays a critical role in the ability to interpret the results meaningfully. Further, algebraic uncoupling of these data plus determination of the deposit yield as a function of charging agent addition allow discrimination between the three main mechanistic stages of the electrokinetics of the process, which are: (1) surface saturation; (2) compression of the diffuse layer, growth of polymer-rich layer, and/or competition between the mobility of Ti and PDADMAC; and (3) little or no decrease in electrophoretic mobility of Ti, establishment of polymer-rich layer, and/or dominance of the mobility of the PDADMAC over that of Ti.