The Effect of Bucky-Ball Nanoparticle Additives on the Electrowetting-on-Dielectric Response of Two Ionic Liquids

Title: The Effect of Bucky-Ball Nanoparticle Additives on the Electrowetting-on-Dielectric Response of Two Ionic Liquids

Abstract for Poster Presentation at the 2013 AIChE Annual Student Conference, November 1-5, San Francisco, California

Authors:  Glenn R. Hafenstine†, Marriner H. Merrill*‡, and James P. Thomas‡

†Chemical Engineering Department; Kansas State University, Manhattan, KS 66506, USA

‡Multifunctional Materials Branch, Code 6350; Naval Research Laboratory (NRL), Washington, DC 20375, USA

*Corresponding Author: marriner.merrill@nrl.navy.mil

Abstract: Electrowetting-on-Dielectric (EWOD) is an effective method for manipulating small volumes of liquids in applications such as lab-on-a-chip systems, e-microreactors, and novel multifunctional materials. EWOD uses an applied electrical potential between a drop of conductive liquid and a dielectric-coated electrode (on a solid substrate) to effect changes in the liquid-solid contact angle.  As the potential is applied, it tends to “spread” the drop out over the drop-substrate interface regions that are electroded, decreasing the contact angle. Ionic liquids are often used in EWOD applications due to their low vapor pressures (non-evaporating) and their wide range of available chemistries. In this work, we evaluate the effect of adding nanoparticles (diameters ranging from 1 to 100’s nm) on the EWOD response (contact angle change with applied potential) for several ionic liquids over a 0 to +/- 200 V applied potential range. Previous research on a dispersion of 7.7 nm quantum dots in an aqueous solvent reported significantly enhanced EWOD response over that predicted by the Lippmann-Young equation. Of the various nanoparticle-IL’s tested in our work, the 0.05 wt% solution of 0.71-nm ‘bucky-balls’ in 1-Butyl-2,3-dimethylimidazolium nitrate (MMBI-NO₃) showed the best improvement in EWOD response (23% decrease in actuating voltage for the same contact angle change). The same nanoparticles added to 1-Ethyl-3-methylimidazolium methyl sulfate (MEI-MeSO₄), however, showed only slight improvement in EWOD response. At this stage of the research, we do not fully understand the role played by the bucky-ball additives in improving EWOD response with the MMBI-NO₃ nor the reason no improvement in response was observed with the bucky-ball additives in MEI-MeSO₄ . Ion chemistry, and nanoparticle dispersion quality and segregation within the droplet are potential mechanisms being investigated. Further testing with several different ionic liquids of varied cations and anions is being conducted to answer these questions.