Towards A Consistent Model For Prediction Of Zeta Potential In Silica Microchannels With Respect To Electrolyte Properties In Thermal Equilibrium
Electroosmosis flow refers to motion of liquids induced by an applied voltage across microchannels.1 This phenomenon has been known for a couple of centuries now and since then it has been used in a variety of technological applications (inkjet printer technology, electrochromatography, isoelectric focusing,etc. [1-3] and is still drawing even more attention from the scientific community particularly because of its relevance to micro-scale technology. Electroosmosis is known to be first formulated in its present form by von Smoluchowski. . He predicted that bulk fluid velocity under application of an external electric field would be equal to: Ub = [-] Eext [zeta] [eta] (0.1) where Eext shows the external electric field applied tangentially to microchannel surface and [eta] and refer to fluid bulk viscosity and electrical permittivity respectively. The [zeta] term was then introduced to represent the scalar electric potential at the so called "shear plane" where the no-slip boundary condition applies. Smoluchowski's formula(2.4) is the most famous, fundamental equation in microfluidics and is used extensively in both research and design applications. Nevertheless and like many other physical formulae, it has been derived by making a few simplifying assumptions that are not necessarily always true. 1 en.wikipedia.org/wiki/Electro-osmosis In One of the early modifications to(2.4), Overbeek and Lyklema , modified the formula and accounted for variability of [eta] and inside the so called "double layer" based on previous evidence from the theory of double layer capacitance in electrochemistry and experiments on the effects of electric field on viscosity of fluids [6, 7]. Recently researchers have studied interesting nonlinear AC electrokinetic phenomenon and come up with new intriguing experiments [8-11]. The novel results of these experiments have once again led researchers to consider modifying the classical equations of electrokinetics in order to explain their experimental observations.  Yet another reason to urge for doing more research on the HelmholtzSmoluchowski classic electokinetic theory comes from undesirable discrepancy between different data sets on [zeta] potential measurements of certain solid-liquid interfaces. Notably Kirby and Hasselbrink, pointed out this problem in their 2004 paper and proposed normalization of measured [zeta] potential by ionic strength of solutions which resulted in a better agreement between the various data sets . The goal of this project which started on May 2009 under professor B.J Kirby's supervision was then to look for a way to either modify the classical electokinetic phenomenon theory or provide interpretation of available data sets on [zeta] potential measurements in the literature such that this discrepancy can be explained. This would result in a better understanding and insight to the physics of double layer theory and fluid mechanics and better models to rely on in engineering design applications where prediction and control of zeta potential in microchannels is crucial.
Healey, Timothy James
Lal, Amit; Kirby, Brian
Theoretical and Applied Mechanics
M.S., Theoretical and Applied Mechanics
Master of Science
dissertation or thesis