Graduation Semester and Year

2010

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Daniel W Armstrong

Abstract

Wettability control of a liquid drop by an external electric field or "electrowet- ting" recently was the subject of special interest among researchers due to its util- ity for a variety of applications. Some of these include "electrowetting on dielectric (EWOD)" based digital microfluidic lab-on-a-chip devices, EWOD lenses and EWOD displays. In these EWOD based devices, water or aqueous electrolytes are used as the liquid medium. However, the use of water or aqueous electrolytes has several limitations and may reduce the efficiency as well as accuracy of these devices. Low thermal stability, evaporation, fouling and fixed phys- iochemical properties are a few of the drawbacks of water and aqueous electrolytes. To overcome these limitations the alternative use of ionic liquids (ILs) in EWOD based devices are suggested in this dissertation.ILs are a special class of non-molecular liquids, which do not evaporate. High thermal stability and tunable physiochemical properties are few of the other unique properties of ILs. In order to use in EWOD based devices, the electrowetting properties of 19 different ILs were examined under DC voltage conditions. All tested ILs showed electrowetting of various magnitudes on an amorphous flouropolymer layer. The effects of IL structure, functionality, and charge density on the electrowetting properties were studied. Compared to water and aqoueous electrolytes, ILs showed enhanced stability at higher voltages.With the obtained clear knowledge of electrowetting behavior of ILs under DC voltage conditions, electrowetting behavior of ILs under AC voltage conditions were examined. Nine different ILs at 3 different AC frequencies (60 Hz, 1 kHz, 10 kHz) were investigated experimentally. The electrowetting properties of ILs were found to be directly related to the frequency of the AC voltage. These relationships were further analyzed and explained theoretically. The electrowetting properties of ILs under AC voltages were compared to that under DC voltages. All tested ILs showed greater apparent contact angle changes with AC voltage conditions than with DC voltage conditions. The effect of structure and charge density also were examined. Electrowetting reversibility of ILs under AC voltage conditions was studied. The physical properties of ILs and their electrowetting properties under both DC and AC voltage conditions were tabulated in order to use as references for the engineering of task-specific electrowetting agents (ILs) for future EWOD based applications. Fur- ther, the study showed that in AC voltage conditions, an EWOD experimental setup acts as a liquid RC filter.Also the study revealed that, the cut-off frequency (fC ) of this type of RC filter is a function of conductivity, dielectric constant, surface tension and double layer thickness of the liquid as well as the applied voltage. That relationship was used to develop a tunable RC filter and an analytical detector. Industrial biocides with different solvents were used to test the performance of this detector. Low limits of detections were achieved for the tested biocides and the detector seems to be broadly applicable and have with very low fabrication costs.

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

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