National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)
Proposal Number: 0730391 Principal Investigators: Sides, Paul Affiliation: Carnegie Mellon University Proposal Title: Investigation of the Zeta Potential of Electrically Polarized Inrterfaces
The field of this research is electrochemically directed self-assembly of colloidal particles on electrodes. A hypothesis about the mechanism behind an experimentally observed electrolyte-dependent motion of colloidal particles near an electrode will be tested. The experimental observation is that a correlation between a phase angle and the aggregation or separation of two particles during ac polarization exists. The expected angle is 90o. The observed angles are less than 90o for KOH and greater than 90o for bicarbonate solution. The particles separate in KOH and aggregate in KOH. This correlation between the phase angle relative to 90o and whether the particles aggregate or separate has been verified for several combinations of electrolyte and electrode. The reason for this solution dependent correlation remains unknown.
The hypothesis is that the required extra force arises from a flow mechanism called "faradaically coupled electroosmosis" (FCEO) driven by interaction of lateral electric field components with charge in the electrode's double layer. FCEO breaks the symmetry of the strong force arising from the "particle based electroosmosis" (PBEO) interaction between the electric field and particles' charge. FCEO modifies the particle behavior such that the particle height and electric field do not exhibit the expected _/2 phase relationship.
The research will improve knowledge of forces important in the formation of ordered layers of particles on surfaces. The potential application areas are sensors and optical technology.
Intellectual Merit The intellectual thrust of this proposal is the hypothesis that electroosmotic flow due to interaction between electric fields and the double layers of the particle and electrode is the key to understanding not only the behavior of a single particle near a polarized electrode but also to understanding the aggregative/separative behavior of multi-particle systems. Proving this hypothesis would complete the understanding of remote assembly of particles. The problem is rich in science and engineering; it involves the combination of colloidal, electrochemical, and hydrodynamic phenomena. The proposed investigation includes novel experimentation and multiphysical electrohydrodynamic computer simulations. The propose investigation is the capstone study necessary to complete the puzzle of this most subtle effect.
Broader Impact The phenomena of this study are of fundamental interest to colloid science and technology. New display technologies employ the interaction of electric fields with particles encapsulated with liquids. Cells, given their charge, can be manipulated by electrohydrodynamic flows and even sorted. Electroosmotic flow is important in technologies beyond the details of this problem, particularly in microfluidic transport of liquids. The new perspectives gained will also support the development of laboratory experiments already inserted into the colloid science curriculum. The research will be a part of the training of a graduate student and undergraduates at Carnegie Mellon, who will become productive agents in the scientific and engineering community.
