title: The zeta potential of PMMA in contact with electrolytes of various conditions: theoretical and experimental investigation.
abstract: Many unit operations required in microfluidics can be realised by electrokinetic phenomena. Electrokinetic phenomena are related to the presence of electrical surface charges of microfluidic substrates in contact with a liquid. As surface charges cannot be directly measured, the zeta potential is considered as the relevant parameter instead. PMMA is an attractive microfluidic substrate since micron-sized features can be manufactured at low costs. However, the existence of PMMA surface charges is not well understood and the zeta potential data found in the literature show significant disagreement. In this article, we present a thorough investigation on the zeta potential of PMMA. We use computations of the potential distribution in the electrical double layer to predict the influence of various electrolyte parameters. The generated knowledge is compared to extensive experiments where we investigate the influence of ionic strength, pH, temperature and the nature of the electrolyte. Our findings imply that two different mechanisms influence the zeta potential depending on the pH value. We propose pure shielding in the acidic and neutral milieus while adsorption of co-ions occurs along with shielding in the alkaline milieu.
authors.affiliation: Department of Chemical Engineering, Queen's University, Kingston, ON, Canada; Queen's-RMC Fuel Cell Research Centre, Queen's University, Kingston, ON, Canada.
authors.forename: Hamid
authors.initials: H
authors.lastname: Falahati
authors.forename: Lambert
authors.initials: L
authors.lastname: Wong
authors.forename: Leila
authors.initials: L
authors.lastname: Davarpanah
authors.forename: Abhinandan
authors.initials: A
authors.lastname: Garg
authors.forename: Peter
authors.initials: P
authors.lastname: Schmitz
authors.forename: Dominik P J
authors.initials: DP
authors.lastname: Barz
mesh_terms: D004573:Electrolytes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D046210:Microfluidic Analytical Techniques; D008962:Models, Theoretical; D009994:Osmolar Concentration; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D013696:Temperature
chemical_list: D004573:Electrolytes; D019904:Polymethyl Methacrylate
keywords: Electrical double layer; Electrokinetic phenomena; Electrophoretic light scattering; PMMA; Zeta potential