Numerial study of induced charge electroosmosis and its applications

• Author / Creator

  Jain, Mranal

• Lab-on-a-chip (LOC) devices promises automation of conventional bio-analytical laboratory tests with little reagent/ sample usage. These devices however require pumping and mixing of samples/reagents in order to attain desired functionalities. Therefore, study of fluid flow at micron length scales, microfluidics, is critical for LOC devices. As the dimensions shrink, the relative importance of surface forces /effects increases with respect to volumetric forces. Due to smaller length scales, there exist several challenges such as: (a) mixing and pumping of fluids where conventional (macroscopic) techniques are not useful or applicable; (b) identifying innovative techniques for fluid manipulation which scales appropriately with the device dimensions. A variety of strategies have been developed for microscopic fluid manipulation. However, electrokinetics is the preferred flow driving mechanism owing to its non-mechanical nature and ease of flow control. On the downside, the plug flow type profile in electrokinetic flow results in poor mixing conditions. Mixing is a key step in realizing fast analysis time in many bio-chemical, biological and detection applications of LOC devices.

  This dissertation deals with the study of induced charge electro-osmosis (ICEO) and its possible applications in microfluidic devices. ICEO is a non-linear variant of classical electrokinetics and deals with electrically induced fluid flow over polarizable surfaces. Initially, theoretical models were developed for induced charge electro-osmotic (ICEO) flow and validated against reported analytical results. A geometrically simple design is proposed for efficient micromixing using ICEO flows. The proposed device is further optimized using NURBS based shape optimization techniques. The transition of optimal shapes from a diffusive regime to an ICEO-dominant regime was demonstrated while identifying rectangular shape and right triangle shape as optimal for diffusive and ICEO dominant regime respectively. For comparison of various parallel flow micro-mixers, a new mixing performance index was developed based on normalized residence time. The proposed comparative mixing index (CMI) is utilized for characterization of various micro-mixing techniques and subsequently, limitations associated with existing mixing performance indicators were identified. Lastly, a concentration gradient generator device is designed based on ICEO flow. The proposed device was found to be superior to existing designs in terms of dynamic controllability due to ICEO flow characteristics. In general, this study demonstrates the use of ICEO for inducing localized variations in fluid flow and utilizes such tailored flow characteristics for attaining specific tasks such as mixing and gradient generation. The presented methodology would be useful in designing micro-devices as well as optimizing their performance.

• Subjects / Keywords

  • Electroosmosis

• Graduation date

  Spring 2011

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3Z03P

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.