UNS: Mechanisms of Surface Charging in Nonpolar Media

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

CBET - 1511619 PI: Schneider, James Many products of technological importance involve suspensions of particles in liquids. This project examines the mechanisms of electrical charge formation on particles immersed in nonpolar liquids. The formation of charges on particles can create electrostatic repulsions between the particles that inhibit their aggregation, which leads to a stable suspension. Certain types of surfactants can be added to the suspension as charging agents to help stabilize the suspension electrostatically. The PI has developed a method to synthesize collections of surfactants with systematic variations in their molecular structures. The surface charging characteristics of these surfactants will be characterized by using two instruments developed by the co-PIs. Results of the project will help test theories of charging in nonpolar media and ultimately lead to the rational design of improved surfactant materials for charging and particle stabilization in nonpolars. Such systems are important in a variety of technologies, including e-readers, oil-based toners for printing, and slow-release fertilizers. The researchers will use the example of the e-reader to engage K-12 students in the basic science underlying display technology and will develop a module for use in university student instruction. This project aims to resolve long-standing questions concerning charge formation in nonpolar solvents by creating libraries of high-purity, custom-synthesized surfactants and studying their propensity to stabilize particles. The synthesis technique gives full control of tail length, extent of branching, headgroup chemistry, and counterion composition. Surface charging will be measured on test surfaces of controlled chemistry using the ZetaSpin method, which makes zeta potential measurements without concern for particle flocculation during the measurement. Inter-particle potentials will be measured by the highly sensitive TIRM method. Elucidation of interparticle potentials will determine if the Gouy-Chapman theory or the counterion-only theory is a valid descriptor of charge screening effects in different systems. The corresponding decay lengths will give a more reliable measure of ionic strength than can be obtained from conductivity measurements. This project will provide valuable insight into the rational design of charging compounds and will help develop new theories to describe inter-particle potentials in doped nonpolars.